Talk:Coandă effect/Archive 1

Archive 1

From PNA/Physics

• Coanda effect - attracts crackpots (due to "flying saucer" relationship), but the current version may be O.K. --Pjacobi 18:14, 24 September 2005 (UTC)

Article content RfC

This article contradicts, or at least seems to contradict Lift_(force)#Common_misconceptions. This should be worked out. —Preceding unsigned comment added by 82.181.17.213 (talk • contribs) Pjacobi 00:17, 25 May 2006 (UTC)

Supporting this anon comment [1], I've put this article on RfC. If we can't verify it the one way or another, we should just drop the content. --Pjacobi 00:15, 25 May 2006 (UTC)

Exactly who is of the opinion that boundary-layer attachment (coanda effect) plays no role in airfoil explanations? Those who put the Coanda effect in the misconceptions section need to justify their actions. Denker's page on airfoils is no justification, since Denker argues that "Coanda Effect" only involves a liquid stream flowing through gas. This is a very odd claim to make. After all, Coanda originally was led to research the boundary layer effects because the output of a jet engine was attaching to the fuselage of Coanda's early jet plane and causing heat damage. Also, the Coanda-effect hovercraft employs a thin radial sheet-jet of gas in a gas environment, as do the Coanda-effect gas burners, etc. "Coanda effect" encompasses fluid flow-attachment in an environment of the same fluid, and so is perfectly legitimate physics: it is part of the legit phenomena known as Stall or as boundary-layer attachment/detachment. --Wjbeaty 00:56, 30 May 2006 (UTC)

Questionable statement

"Professional aerodynamicists regard this theory as a fallacy." I'm skeptical. Please point out which aerodynamicists. --Wjbeaty 01:21, 30 May 2006 (UTC)

This statement is wrong, so I'm fixing it: "The flow from high speed jet produces enhanced lift through turbulent mixing that does not occur above a normal wing." On the contrary, conventional wings remain out of stall because of turbulent mixing in the boundary layer. As I understand this, the only wings which don't employ turbulent mixing are the so-called "Laminar flow" wings. So in other words, "Coanda effect" does apply to wings: it's part of the normal boundary layer physics, and part of the phenomena of Stall. On the other hand, the flow from a high speed jet above the wing will actively enhance the lift (rather than just delaying stall,) because, as the jet remains attached to the curved surface, its curved streamlines lead both to a lowered pressure above the wing, and also to a downward deflection of massive air parcels. --Wjbeaty 01:09, 30 May 2006 (UTC)

Effect photo

I added an actual photo of the effect because...why not? Axda0002 03:21, 21 June 2006 (UTC)

I think that is a good illustrative image. --Profero 15:35, 21 June 2006 (UTC)

test patient-001

Is the reference to test patient-001 in the article of interest to anyone or noteworthy? There's no article in Wikipedia about them, so I'm assuming that they're not well known whatsoever. I went to the link in the article and their website doesn't have much in the way of...information of any kind (save for one song download). I say remove that section. Any objections? Axda0002 02:30, 22 June 2006 (UTC)

After I removed this section, it has reappeared as an edit by 65.78.214.112. It reads:

The Coanda Effect is a progessive metal band from Point Pleasant, WV. They have an album due out this fall and you can find out more at http://www.terraincognita.echoz.com. The band is made up of guitarist Matthew King, singer James Lilly, and bassist Noah Tyree. The percussion is created digitally using computer generated drums.

This is inappropriate for this article. First of all, it smacks as an advertisement. Second of all, this is an article pertaining to a physical phenomenon, not music. If the user feels that this band is notable, which they aren't, then they should be bold in creating an disambiguation page. Axda0002 23:44, 29 June 2006 (UTC)

Cause

At present, the article completely lacks any explanations of the causes of the effect, merely giving its applications. --82.181.61.48 22:13, 18 August 2006 (UTC)

Demonstration image

Link to moving images

I took the liberty to modify the image made by Eli_the_Bearded used in this article. I interpreted the "Demonstration" part of the article in this way: there are mainly four stages represented by the four images in the animation loop: 1) Only water running. 2) The convex object brought close to the waterstream. 3) The "Venturi effect" creating a pressure decrease in the air between and thus bringing the stream towards the object. 4) The "Coanda effect" taking over. I hope this modification can be useful. --Profero 02:06, 30 May 2006 (UTC)

I hate to say it, but even though this image does a good job of demonstrating the effect, it is obnoxious and distracting. Perhaps the GIF can be turned into a sequence of images instead? Either way, it can't stay how it is. Axda0002 03:08, 21 June 2006 (UTC)

I agree with you that animations, especially on the article pages, are most often very distracting. Although I don't know if this one is more distracting than the one in the article, there should be an easy way to start and stop them, or link to them. Yes, you are right, they are often obnoxious too. Perhaps a good idea is to generally create sub-articles containing movies and animations? So I made this still image with link as a suggestion. --Profero 11:18, 21 June 2006 (UTC)

I think that's a good suggestion. Either that, or have the image currently on the article page loop only once or twice. That way, the animation will terminate on the frame that is most descriptive of the effect. Axda0002 13:49, 21 June 2006 (UTC)

I think that if an animation stops, one should be able to start it again without reloading the complete page. I don't know if this is possible. Perhaps you know? In any case I also think that your suggestion of also (or alternatively) showing the individual sequences one by one would be a very good idea in a lot of cases, as they would be easier to understand. After all we are working with computers and should use the potentials we can to best illustrate articles – even more underlining the good idea of having separate good illustration pages with optimal imagery and not clogging up the text. (If you like you can perhaps also share your opinions at The deletion talk page and/or on Talk:Coandă_effect_movies concerning this issue.) --Profero 15:33, 21 June 2006 (UTC)

now a still is referenced? why not LINK to the moving http://commons.wikimedia.org/wiki/Image:Venturi-and-Coanda-effect-2.gif (but i do not know how to techincally do it...) :21:26, 9 April 2007 (UTC)

light and the coanda effect

it would seem that light also bends round and 'sticks' to objects, expecially convex ones. might not gravity also - and in which case - could this be made use of? —Preceding unsigned comment added by 203.27.90.208 (talk) 01:58, 12 October 2007 (UTC)

Aerospike Engine

Is the Coanda Effect employed in the (linear) Aerospike Engine, causing the exhaust flame to adhere to the vane? LorenzoB 04:32, 21 October 2007 (UTC)

WikiProject class rating

This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 09:46, 10 November 2007 (UTC)

Causes, definition, limitations, citations

Although the article is pretty good considering the amount of misinformation surrounding the Coanda effect, one body citation (zero before I put one in) isn't enough in the body. There is a wealth of scientific literature on the effect; Henri Coanda is neither the beginning nor the end. He didn't discover it (it was known as far back as 1800, probably observed earlier) or explain the causes of it (which is still a topic of active research). He just happened to patent a significant application. These are some of my specific concerns:

1) The causes section is lacking and contradictory. It should at least not offer two explanations for the thin jet attached to a spoon, but should also offer a more complete and referenced explanation, covering the current state of the research.

2) The Coanda effect is not a synonym for "boundary layer attachment" and convexity is not a necessary condition. I addressed these problems with the definition by inserting is the most most general definition, which is common enough in the literature that it doesn't need to be cited.

3) There should be some discussion about the limited applicability of the effect or discussion of popular misconceptions, perhaps integrating this article with the mention in the Lift article. It's appropriately limited to a jet of fluid impinging on a curved surface, but there are still other references online that incorrectly lift as consequence of the effect. The article, thankfully, does not make the lift claim. But it comes up frequently enough still that it needs a mention.

I'll return to it when I have time, but for now I put the unsourced tag on to to alert the reader to check the facts and be careful about taking it as the definitive reference. Mbelisle (talk) 01:46, 18 April 2008 (UTC)

Working models

Photos and videos of two radio controlled flying models that use the Coanda effect. http://jlnlabs.online.fr/gfsuav/index.htm —Preceding unsigned comment added by Bizzybody (talk • contribs) 00:46, 30 May 2008 (UTC)

An attempt to clarify "Coanda effect" and "boundary-layer attachment"

In this article and the article on the lift force, and especially in the discussion pages that go with them, there seems to be considerable confusion regarding how the Coanda effect relates to boundary-layer attachment in ordinary aerodynamic flows. Here is an attempt to clarify the issues.

What the term "Coanda effect" properly encompasses

The work that Coanda himself did, which resulted later in the coining of the term "Coanda effect", was limited to powered jet flows in which the jet is of the same phase (gas or liquid) as the surrounding fluid and has higher total-pressure than the surrounding fluid. The phenomenon that Coanda observed was the tendency of a relatively thin jet to attach itself to an adjacent solid surface, and it is due to the strong tendency of jets, especially turbulent jets, to entrain surrounding fluid. The boundary layer in an ordinary aerodynamic flow is not a jet, and its tendency to remain attached is not a direct result of entrainment, so it seems that to apply the term "Coanda effect" to flow-attachment phenomena in general would be to broaden it far beyond what it originally meant. I am a practicing aerodynamicist, and I have discussed this issue with a number of my colleagues. I have yet to find one who thinks that the term "Coanda effect" properly applies to flows other than powered jets.

The phenomenon in which a small vertical stream of water from a faucet deviates from its original vertical path and follows a curved surface is obviously not a result of the same turbulent-jet entrainment that is responsible for the regular Coanda effect. Instead it seems to be due to an actual molecular attraction between the liquid and the solid surface, and to the fact that the stream resists being torn apart, because of the surface tension. So it seems improper to cite this as an example of the Coanda effect.

It also seems improper to apply "Coanda effect" to the flow around an ordinary airfoil, as is advocated by Wjbeaty and has been done in books by Anderson and Eberhardt, and by Craig. But the problem is not just one of semantics. Those who have introduced "Coanda effect" into the discussion of airfoils and lift seem to be under some misapprehensions regarding how flow attachment happens in general, which brings us to the next topic.

What "flow attachment" or "boundary-layer attachment" really involves

Anderson and Eberhardt erroneously see the Coanda effect as implying that viscosity (or turbulence) plays a direct role in the ability of an ordinary aerodynamic flow to follow a curved surface. They assert that viscous forces in the boundary layer tend to make the flow turn toward the surface, specifically, as they put it, that the "differences in speed in adjacent layers cause shear forces, which cause the flow of the fluid to want to bend in the direction of the slower layer". Actually, there is no basis in the physics for any direct relationship between shear forces and the tendency of the flow to follow a curved path. To arrive at a correct understanding of the role of viscosity, it helps to look first at what would happen without it, and then to look at what happens when it is present.

Much of the early theoretical work in fluid mechanics dealt with inviscid ("ideal") flow, and solutions were generated for 2D inviscid flows around many simple body shapes, including airfoils. In the theoretical inviscid world, flows follow curved surfaces just fine without aid from the effects of viscosity, contrary to what Anderson and Eberhardt claim. To support their position, Anderson and Eberhardt argue that the need for a Kutta condition in inviscid airfoil theory somehow demonstrates that inviscid flows don't naturally follow curved surfaces. This is incorrect. The Kutta condition just determines how far along the airfoil chord the flow follows the surface, not whether it follows the surface. The Kutta condition simply rules out flow patterns in which the flow has to whip around the sharp trailing edge, and a correct physical interpretation of it is that it is viscosity that prevents such flow patterns. But this by itself implies a direct role for viscosity only in the immediate vicinity of the trailing edge, not all along the surface, as Anderson and Eberhardt assert. In any case, theory tells us that fluids without viscosity would have no trouble following curved surfaces.

Real-life fluids not only have viscosity, but they interact with solid surfaces in such a way that the tangential velocities of the fluid and the solid are matched at the interface (the no-slip condition). At all but very low Reynolds numbers, a thin boundary layer in which viscous effects are important forms along the surface, and outside of the boundary layer the flow behaves as if it were inviscid. Near the front of a body, the boundary-layer flow is usually laminar, but in most cases of practical interest it transitions to a turbulent state before it reaches the back of the body. Over a wide range of conditions, the natural state of a laminar or turbulent boundary layer is to remain thin and to remain attached to the surface. But under some conditions, the boundary layer will separate from the surface. What determines whether the boundary layer separates or stays attached?

Within the boundary layer upstream of separation, the flow velocity is nearly parallel to the local solid surface. The distribution of this surface-parallel velocity with distance off the surface, from zero at a stationary surface, to a high velocity at the edge of the boundary layer, is referred to as the velocity profile. In addition to viscosity, the velocity profile is strongly influenced by the pressure distribution in the flow direction (parallel to the surface). The curvature of the surface has almost no direct effect, but only an indirect one to the extent that surface curvature affects the pressure distribution. Whether the boundary layer separates or stays attached depends on what happens to the low-velocity fluid at the very bottom of the boundary layer, which is strongly influenced by the pressure gradient in the local streamwise direction. If the pressure is constant or decreasing (a favorable pressure gradient), the low-velocity fluid will continue to move in the direction of the local surface, and the boundary layer will remain attached. Boundary-layer separation from a smooth surface in a 2D flow generally requires rising pressure (an adverse pressure gradient) to stagnate the low-velocity fluid. Counteracting the effect of an adverse pressure gradient are the viscous forces by which the higher-velocity fluid farther from the surface drags the low-velocity fluid along. So boundary-layer separation is determined by a tug-of-war between an adverse pressure gradient and favorable viscous forces. If the adverse pressure gradient is not too strong, the viscous forces will win, and the boundary layer will remain attached, just like the corresponding inviscid flow would under the same conditions. The amount of adverse pressure gradient that can be withstood is greater if the boundary layer is turbulent than if it is laminar, which is why even so-called laminar-flow airfoils are generally designed to have laminar flow only over part of the airfoil chord, with the boundary layer transitioning to turbulent before it encounters the strong adverse pressure gradient that usually prevails over the aft part of the airfoil.

A turbulent boundary layer's resistance to separation improves as the Reynolds number increases, no matter how high the Reynolds number becomes. Thus Wjbeaty's supposition that an airfoil flow at an extremely high Reynolds number would always be stalled is incorrect.

We've seen that the role of viscous forces in maintaining boundary-layer attachment is to help the low-velocity fluid at the bottom of the boundary layer keep moving, and that the viscous forces are needed only in situations where the pressure gradient is adverse. Viscous forces have nothing direct to do with causing the flow to turn and follow a curved surface. However there is an indirect association between surface curvature and the need for viscous effects that may have contributed to Anderson and Eberhardt's confusion in this regard. Convex surface curvature is often, though not always, associated with an adverse pressure gradient, in which case favorable viscous forces are needed to prevent separation. But the viscous forces prevent separation by dragging fluid along in the direction of the local flow, not by directly contributing to the turning of the flow.

If viscous forces make no direct contribution to the turning of the flow when the surface is curved, what actually causes the flow to turn? The answer to this question lies in the interplay between the velocity field and the pressure field, which works in the same way whether the fluid is viscous or not. When a flow turns to follow a curved surface, it is able to do so because the pressure field adjusts so as to provide the force needed to accelerate the fluid toward the center of curvature. Thus the centrifugal force generated when the flow follows a curved path is countered by a pressure gradient perpendicular, or normal, to the local flow direction. The normal pressure gradient and the flow curvature have a reciprocal relationship in which they cause and support each other simultaneously. Note that the normal pressure gradient is perpendicular to the streamwise pressure gradient that we considered earlier, and that it is the streamwise pressure gradient that plays the important role in determining whether the viscous boundary layer separates or remains attached.

A good counterexample to the Anderson and Eberhardt argument is the flow around a rotating circular cylinder. Tangential motion of a surface, due to rotation, can affect the location of separation. In this case, the flow follows the curved surface farther around the side of the cylinder where the surface is moving with the flow, and separates earlier from the side on which the surface is moving against the flow. But if we apply the Anderson and Eberhardt argument to this flow, it predicts the opposite of what is observed. On the side where the surface is moving with the flow, the viscous stresses are reduced or even reversed, and the ability of the flow to follow the curved surface should be reduced, according to their argument, but in fact it is enhanced. And vice-versa for the other side of the cylinder. The observed effects on both sides are consistent with ordinary boundary-layer theory, which correctly accounts for the effects of pressure gradient and surface motion.

What this indicates for the encyclopedia articles

The article on lift should point out that attachment of the flow to the airfoil upper surface is important, but that attached boundary-layer flow is the normally expected condition up until stall, and that the "Coanda effect" is not applicable. The article on the Coanda effect should be revised so as not to conflate the effect with ordinary "boundary-layer attachment". It should also explain what the effect really is and how it works, not just assign a name to it and give examples of where it occurs. Of course the water-faucet example should either be removed, or it should be revised to explain how this effect differs from the real Coanda effect. J Doug McLean 20:39, 4 December 2006 (UTC)

Excellent posting! Let me try to drill down to three critical issues. First one. You say 'The boundary layer in an ordinary aerodynamic flow is not a jet, and its tendency to remain attached is not a direct result of entrainment.' Interesting. Here's a thought experiment. Suppose we have an enormously wide jet which flows over a cylinder. This would be an example of boundary layer attachment, agreed? (Let the width of the jet be >> than the cylinder diameter. Assume laminar flow for clarity.) If we then let this jet decrease in width, eventually we'll arrive at a "Coanda effect" situation. I'd like to understand why there is a fundamental difference between the mechanism which attaches a wide jet, versus the mechanism which attaches a narrow jet. Why is a narrow jet attached by entrainment, while a wide jet is not? (Or equivalently, why is a narrow jet *not* attached by boundary layer pressure distribution, while a wide jet is?) Also, as we go from a wide jet to a narrow one, if the attachment mechanisms change completely, then what does the transition from "entrainment" to "boundary layer attachment" look like? I ask because I'm under the impression that there is no difference between attachment mechanisms, and that they are just two alternate approaches for explaining a single phenomenon. --Wjbeaty 05:49, 5 December 2006 (UTC)

You're right that the distinction between ordinary boundary-layer attachment and flow attachment in flows involving jets isn't always as clear-cut as I made it out to be in my posting. You make a very good point that you can define a continuum of situations between a thin jet and a thick one, and that there is no apparent switchover from one physical phenomenon to another. But I don't think that means that we're dealing with just one physical mechanism across the whole possible spectrum of such flows, and I'm going to argue that we should still maintain a clear distinction in our terminology.

To define what I consider to be the purest prototype of the Coanda effect I'd ask you to go a step beyond your thin-jet-to-thick-jet thought experiment. Consider a thin jet issuing from a nozzle that is separate from any downstream surface to which the jet might attach. The nozzle exit has sharp edges from which the internal flow separates cleanly as it leaves the exit, and a free jet is formed downstream of the exit Even if the nozzle flow isn't turbulent, the jet downstream quickly becomes turbulent For simplicity, think of a 2D flow from a slot nozzle, issuing into otherwise still air. In the absence of an attachment surface downstream, we get a classic 2D turbulent free jet that flows straight out along the nozzle axis. Now bring a 2D, curved attachment surface in from above or below the jet, a 2D version of the spoon in the faucet-and-spoon illustration in the article, but in this case it is in a single-phase flow. Even before the 2D spoon reaches the edge of the turbulent jet, the jet will be drawn to the surface and attach to it. The jet goes "out of its way" to attach to a surface that is entirely outside the former boundary of the turbulent free jet. This kind of attachment is clearly due to turbulent entrainment and would not happen in the absence of viscosity or turbulence. The corresponding steady inviscid-flow "solution" in this situation is a straight, constant width stream of fluid with higher total pressure than the surroundings, separated from the surroundings by zero-thickness slip surfaces. Until the spoon actually touches this stream, no steady, inviscid attached-flow solution is possible. So there is a range of spoon positions for which the viscous (turbulent) flow would be attached to the surface, but for which no inviscid attached-flow solution exists.

There is thus a sharp distinction between this prototypical version of the Coanda effect and ordinary airfoil flows, because in the case of an airfoil in an external stream, attached flow solutions exist for both the viscous and inviscid cases. In other words, in the prototypical Coanda case we need viscosity (turbulence, actually) to establish any attachment at all, while in the airfoil case we don't.

But for jet flows in which the nozzle is not distinct from the attachment surface, as for example when the downstream surface is an extension of one wall of the nozzle, we no longer have this sharp distinction. This situation, in which the jet starts out attached to a surface, is often referred to as a "wall jet". Whether such a jet is a thick one with a non-turbulent "core", or a thin one with an external flow outside of it, the situation is more like that of an ordinary boundary layer in an external flow, for which attached flow is the expected condition up until an adverse pressure gradient is strong enough to cause separation. In these wall-jet cases in which the nozzle fairs smoothly into the attachment surface, attached-flow solutions exist in the inviscid case, and viscosity is not needed to establish or maintain attachment any more than it is in ordinary boundary-layer attachment. This also means that the prototypical Coanda case, in which the jet starts out free and then attaches itself to the surface is the only one that needs entrainment to establish attachment, and that the cases in which the jet starts out already attached don't need entrainment. This particular distinction hadn't occurred to me when I wrote the above posting, so I'm glad you brought the issue up. Perhaps we should recognize a distinction between a "free-jet Coanda effect" (my "prototypical" case) and a "wall-jet Coanda effect", but in cases with a moving external flow, the wall-jet version would just be another name for the well-known technique of delaying boundary-layer separation by tangential blowing, which might be giving Coanda more credit than he deserves.

As I pointed out in the posting, in ordinary boundary-layer attachment, viscosity is needed to maintain attachment only when the pressure gradient is adverse, and even then the role of viscosity isn't the same as the direct role implied by Anderson and Eberhardt. So I still think we should avoid using the term "Coanda effect" in connection with ordinary airfoil flows because it implies that viscosity plays a much more direct role in maintaining attachment than it does in reality. J Doug McLean 01:48, 10 December 2006 (UTC)

I respect your expertise in this area, but I think your expertise regarding the differences in the types of flows has blinded you to the obvious commonalities, in particular, the aerodynamic mechanisms at play. You state that "this kind of attachment . . . would not happen in the absence of viscosity or turbulence." Fair enough. Now give me an example of a fluid that has no viscosity. Air has viscosity, and as air travels over an air foil, it is pulled down in conformance with the air foil shape because the pressure differentials above and below the stream. The pressure below, is reduced as a result of entrainment, shear, and viscosity (all inter-related concepts). Therefore the mechanism at play in your "prototypical version" of the Coanda effect is the same as in the instance of airfoils. If the mechanism at play is the same, why not use the same term, as it is descriptive of the mechanism? --Lenehey 21:50, 17 June 2007 (UTC)

I think J Doug McLean's posting is about as accurate treatise of this topic as I've come across. Can I add that I emailed Scott Eberhardt of Understanding Flight, by David Anderson and Scott Eberhardt, some years ago and he told me that they did not intend to imply that the Coanda Effect has anything to do with lift on a aerofoil. He said they used it to explain Newton's Laws to the layman and were considering removing it in future editions as there was so much resulting controversy. I got the impression that his co-author saw more value in mentioning the coanda effect than he did. Tt261 (talk) 18:16, 13 May 2008 (UTC)

If Scott Eberhardt said he and Anderson "did not intend to imply that the Coanda Effect has anything to do with lift on a aerofoil" I don't believe him. On page 21 of Understanding Flight it says "This downward-traveling air is the downwash and as we will see is the source of lift on a wing. Why does the air bend around the wing? The answer is in an interesting phenomenon called the Coanda effect. The Coanda effect has to do with the bending of fluids around an object."
See my critique of the book at Talk:Bernoulli's principle/Archive 2#Understanding flight. I'm not surprised there was great controversy about the book's contents - the book is scientifically unsound on many points. Dolphin51 (talk) 02:49, 27 October 2008 (UTC)

News from France

The so-called Coanda effect strongly depends upon a largely ignored factor, viz: the width of the defllected jet, as compared with its radius of curvature. Appropriate experiences show that Coanda effect does not occur at all if the ratio width/radius is greater than 0.3: obviously the Coanda version of stall.

Extensive information about this factor can be found in the wikipedia french edition “effet coanda”: see the article, then the page 9A in the pdf in reference 6, and the discussion which provides photos with additional information in wikipedia commons.

The same experimental information is available in english in the following reference:

Kadosch M., “The curved wall effect” in 2nd Cranfield Fluidics Conference, CAMBRIDGE 3 Jan 1967 --Marcel kadosch (talk) 14:03, 10 February 2009 (UTC)

Does the Coanda effect occur in a vacuum?

Anyone know? (Stream of water against the back of a spoon, would the path of water be be pulled across the curve of the spoon, or would they bounce off?)

It would certainly help in the aerodynamic lift confusion. Please supply references.--JayJayPlant 16:15, 8 August 2006 (UTC)

If it were possible to test in a vacuum it wouldn't occur. In a vacuum, the water would instantly vaporize. The gas would instantly disperse. However, if you could somehow keep these two things from happening, there would be no pressure differential caused by entrainment of surrounding fluid to force the steam against the airfoil/spoon.

Your proposed experiment can be prefoermed if you use a stream of liquid mercury kept at a low temperature to minimize the presence of mercury vapor. My suggestion is at a temperature, T in Kelvin, such that 235K < T < 315K which should place the vapor pressure below 1Pa according to the information provided @ http://en.wikipedia.org/wiki/Mercury_(element) . Jatosado (talk) 21:31, 31 July 2009 (UTC)

Experimental material

Sept 24, 2009

Defining Coanda effect just as the tendency of a fluid jet to be attracted to any nearby surface is questionable, and Coanda effect is also limited as follows.

-Assume first the nearby surface to be convex towards the jet : in most of quoted applications which involve a rather high Reynolds number: Re = vb/kinematic viscosity , where v is the mean fluid velocity and the length b is the lateral extension (or width) of the jet, the fluid jet is attracted only if the ratio: R/b = radius of curvature/width of the jet ≥3, as measured by Kadosch M., see: “Déviation d’un jet par adhérence à une paroi convexe” in:

Journal de Physique et Le Radium, avril 1958, p 9, or : ajp-jphysap_1958_19_S4_A1_0.pdf p 9,

The fluid jet is separated when R/b <3

The critical ratio R/b at which the jet is separated increases at small Reynolds numbers: up to R/b =7 if Re = 500, R/b=10 if Re=200, and to R/b = 20 if Re=100, as measured by T. Vit , F. Marsik , see: “Experimental and theoretical study of heated coanda jet” in:

fluid.ippt.gov.pl/ictam04/text/sessions/.../FM2_12062.pdf, 2004.

-If the nearby surface is a flat plate at an angle a , the jet is first separated then re-attached further at a significant length, when a increases from 30° to 60° or decreases with an hysteresis of 15°, as measured by Bourque C. and Newman B.G. , see: “Reattachment of a two-dimensional, incompressible jet to an adjacent Flat Plate “,in:

The Aeronautical Quarterly, vol XI, aug 1960; pp 201 and seq.

If a< 30°, the bubble of separation is too small and its length is not significant.

- What if the nearby surface is concave? Why not test the popular spoon suspended under a jet getting into the spoon instead of around? Surface tension or not, the spoon is thrown out and the formerly deflected jet is straight again , then the spoon comes back and is thrown again etc, a relaxation oscillation occurs, with a period depending upon the mass flow.

Now an impulse turbine (a Pelton wheel) may be thought of as a number of spoons mounted on the same axis for continuous rotation. Most people believe that the jet impulse spins the wheel, but Coanda-lovers may argue that the wheel is spinned by the attraction of the jet to the back surface of the spoons. This is no longer physics, just metaphysics --Marcel kadosch (talk) 22:55, 23 September 2009 (UTC)

Fundamental flaws in this article

This article constantly mixes up the attraction of liquid to a surface (which is caused by a molecular attraction between the two) and flow over aircraft wings (which involves no such molecular attractions). There is no way this is the same thing. Precisely what the Coanda effect is needs to be agreed upon and used consistently. —Preceding unsigned comment added by 74.197.181.171 (talk) 06:40, 4 November 2009 (UTC)

Answer to 74.197.181.171, and additional experiments

Maybe I am mistaken (I speak french) but I understood that “ in this article” means “in the above article”, titled: "Experimental material". All the quoted experiences concern Coanda effect with air jets attracted by a nearby convex or flat surface. I suggested to add an experience concerning either Coanda effect (gaz jet in gaz) or Teapot effect (liquid jet in air), surface tension or not, when the nearby surface is concave: an extension which is involved by the new definition of Coanda effect introduced by Kim Aaron in the article “Coanda effect”, 8 september 2009, as given by Tritton: he does not quote him for copyright reasons, and unfortunately I could not read him. But many people say:”when I hear the word Coanda, I reach for my spoon”: that’s what I did.

Meanwhile I take the permission to quote the experiences made by C. Duez et al, who finally discovered the real cause of the teapot effect: “a novel hydrocapillary adhesion phenomenon coupling inertial flows to a capillary adhesion mechanism”, and took a laser photograph of it! See it in:

"Wetting controls separation of inertial flows from solid surfaces", C. Duez, C. Ybert, C. Clanet, L. Bocquet, Physical Review Letters 104 084503 (2010). --Marcel kadosch (talk) 21:18, 15 April 2011 (UTC)

Image at top of article

Is anyone interested in making a higher-quality one? No offense to the OP, but kinda unclear and low-budget looking atm. a13ean (talk) 17:51, 8 October 2012 (UTC)

I've gone ahead and replaced it with a photo from Commons -- 82.32.198.178 (talk) 20:55, 8 October 2012 (UTC)

New Material Added

Sept. 8, 2009

Kim Aaron, PhD Aeronautics, Caltech 1985.

I revised the discussion quite a bit today. I rewrote the "Causes" section to match the explanation as I learned it at Caltech. I supplied an honest-to-goodness text book as a reference which shows very convincing photographs of the phenomenon and explains it the same way I learned it. I have not scanned those images and pasted them in due to copyright reasons. I'm talking about "Physical Fluid Dynamics" by D.J. Tritton. It is an excellent book explaining all kinds of fluid phenomena in easy to understand language. When I purchased the paperback version in the early 1980's, it cost me $11.55. Of course, with inflation, that will be higher now, but it's a very reasonable price and I highly recommend it.

I particularly revised the demonstration of the spoon in a stream of tap water to explain that it is NOT due to the Coanda effect, but is rather due to surface tension. I also added a few real examples.

_____

Let me add my two cents to the discussion above about flow past a wing. When a wing moves through the air, there is no concentrated jet. Just because there is shear in the boundary layer does not mean it is an example of the Coanda effect. It is true that the flow resembles what would happen if you aimed a jet over the top of the wing in that the flow remains attached to the upper surface and the flow follows a curved path over the top (and the associated change of momentum contributes to the lift on the wing). But in the main uniform flow past a normal wing in flight, there is no entrainment. At best, there is the potential to entrain flow where the wing is because the boundary layer would try to mix with fluid that would be where the wing is if the wing were suddenly not there. But that is really a stretch in calling it Coanda effect. Really, the fluid tries to stay attached to the wing due to continuity of material. The pressure distributes itself to try to make that so. When the fluid does break away from the surface (during stall), then there will be entrainment along the highly sheared flow, and in some circumstances, that entrainment will pull the flow back down to the surface leading to reattachment. That might reasonably be cited as as example of the Coanda effect, although I personally don't think of that as being Coanda effect. Lots of things can be going on in a fluid flow and they bear resemblance to similar but different flow situations. Because one thing looks like another does not mean it *is* that other thing.

Kimaaron (talk) 21:54, 8 September 2009 (UTC)

Deleted this image because it is misleading:

Demonstration of Coandă effect

It looks like the spoon in the stream of water, which I have discussed as being NOT an example of the Coanda effect.

Kimaaron (talk) 22:44, 8 September 2009 (UTC)

• If it's not right, it's not right. I'm no expert. I created that image because that's what I'd been led to believe the Coandă effect was, and the article didn't make it clear. Can you create an illustration that is more accurate? --Elijah (talk) 22:58, 10 September 2009 (UTC)

It is a great illustration of the flow past the back of the spoon, which previous editors had described as illustrating the Coanda Effect (a VERY common misunderstanding). There are some photographs in the book I cited (Tritton) that illustrate the Coanda Effect very well. I wish I could simply scan them and paste them in, but that would violate copyrights. Maybe I will write the publisher and ask for permission to display the images (with appropriate credit). in the meantime, I'm not sure exactly what a replacement image should look like. I'll think about it. Maybe I can come up with something. Maybe I'll sketch something by hand, scan it, and put it in the discussion so someone with the right skills can reproduce it in a similar illustration to what you produced so well.

Kimaaron (talk) 05:58, 11 September 2009 (UTC)

Well your PhD was three years before mine so I guess you take precedence although I don't know about Caltech versus Cambridge. However I think the wording of the explanation should be more along the lines of "one useful way to understand it is". There are a whole load of ways to understand Coanda including from Bernoulli, Newton's Laws and entrainment. All of these can be done right or wrong, and each have their share of people who think they do not work because they have only heard a wrong explanation based on them. The trouble with entrainment as an explanation is that it is quite a difficult concept to start with. Of course explaining to graduate students that way is one thing but Wikipedia might manage explanations with fewer intermediate steps. The Oxford English dictionary used to be criticised for defining pepper as a "pungent aromatic condiment" which gave a child three words to look up instead of one. Coanda is a similar level of concept to entrainment and not really reliably defined in terms of it. :)--BozMo talk 13:26, 11 September 2009 (UTC)

Y'all might want to add this too. The Ching disc golf company claims that it's putter takes advantage of the coanda effect from the indentations "contours" in the flight plate of their putter. here is the link. they have a patent and everything, haha. http://www.ching.us.com/sports/index.php/d-r-a-f-t-systems Grrbrown (talk) 02:49, 31 March 2013 (UTC)

Prior to Frost

I recently, some time about a month ago, came across a diagram of a vehicle that used the disks that Frost was experimenting with in the image seen here: [2]. This was part of a UK research group's output from the WWII era, and the imaged showed four of these disks arranged around the corner of a bus-like vehicle. It suggests that Frost's work was inspired by this group, which is certain worth mentioning. Has anyone else seen this image? Maury Markowitz (talk) 11:23, 26 August 2013 (UTC)

Ping-Pong Demonstration Section

Most focus is on the effect, so the ping-pong section was overlooked. My correction addresses the following:

A) The air does not necessarily curve all the way to a downward direction. It only has to have enough downward acceleration for M*A to equal the very light ball's weight. This may only be a small change (reduction) in the vertical component with an additional small horizontal component set by the jet's off-vertical angle. Testing with a handball sized ball and a cotton tuft probe showed a 70 degree total change in airflow direction from 20 degrees off vertical to horizontal.

B) Using the word "suction" mirrors the false explanation of lift using Bernoulli's pressure difference and ignores the air momentum change and the required reactive force.

In addition, a hefty vacuum cleaner can blow a ping-pong ball across the room, so something heavier is recommended (ball or light bulb), or a lighter air stream. A heavier ball should also show more total air-stream deflection.

Also, I see a common objection to calling sheet adhesion the Coanda effect. I won't inject my opinion into the discussion of whether it is a jet vs. sheet being the Coanda effect but say that Coanda's initial 1936 US patent, 2,052,869, explicitly recognizes an adhesion effect in both jet and sheet form factor. In addition, his aircraft had a sheet rather than a small jet. So perhaps it is what von Kármán originally defined it as. I also recognize that writing a good patent requires using the most general description possible, so perhaps Coanda was generalizing, with no basis, to the sheet form factor. -- Steve -- (talk) 01:07, 8 July 2014 (UTC)

Discovery Section

1) This quote from the Discovery is incorrect as well as inappropriate here. I removed it:

"This effect is most noticeable near a curved surface, where the air stream

has to speed up near the convex side, and hence lose pressure. Natural

molecular movement in the air tends to equalise the overall pressure, and

pushes in free air, which joins the original jet along the same trajectory as the

convex side of the surface. In turn, this generates lift against the convex surface"

This is expressing "Bad Bernoulli"; i.e. fast air creates low pressure and "sucks-in" surrounding air. This is equivalent to saying that expressing Ohm's law in the form R=E/I shows that increasing the voltage on a resistor causes its resistance to increase.

I believe the following is a cogent path through the science that dispels this misunderstanding FOR CURVED PATHS.

Velocity is a vector quantity and is composed of both speed and direction. Acceleration is a change in velocity (speed and/or direction). Accelerating a mass requires a force. An orbiting satellite travels at a constant speed, but is continuously accelerated radially by the force of gravity. The curved path does not cause the force of gravity [at least not in the non-relativistic arena of fluids]. A mass of fluid is no different. A curved streamline is evidence of a force perpendicular to the streamlines. There must be less pressure on the inside of the curve and more on the outside, thus "pushing" the stream radially inward. With this evidence of a force accelerating the fluid path, one may choose to debate the cause of the pressure gradient, but not that the curved path causes the pressure gradient. Something causes the pressure gradient, and it is clearly something going on with the convex curve and fluid flow. you may debate why the shape causes the pressure profile, but not what causes curved flows.

Babinbski, in his otherwise excellent explanation of Bernoulli and curved flows, shows this pressure gradient is the cause, not the effect. Because it is not his purpose, he ignores what causes the gradient and, unfortunately, describes it blandly as Coanda. Watch Babinski if this confuses you:

https://www.youtube.com/watch?v=XWdNEGr53Gw

His slides. Click the Download Icon for complete set:

https://docs.google.com/file/d/0B0JABuFvb_G_MkpBZHJmRGo3UkU/edit?usp=sharing

The 2003 equivalent article he mentions in the video:

http://www3.eng.cam.ac.uk/outreach/Project-resources/Senior-glider/howwingswork.pdf

-- Steve -- (talk) 04:17, 12 October 2014 (UTC)

Coanda forced, or not forced over wings

I am not sure if this has been resolved due to the length of the Talk section.

2) My understanding in my research talking with a highly regarded aerodynamicist, indicates that, as expressed above in talk, the Coanda effect is a very specific effect considered to be only in regard to what are "forced", high speed jets, or sheets of fluid along a surface in otherwise (or relatively) still fluid. This was called 'Boundary layer Control" in the F-104, and others more recently, to lower the landing speed. It is not used to describe the flow along a surface due only to the relative movement between the fluid and surface as in an ordinary wing generating normal lift. It is more of a definition. If you choose, you may argue that these two flows have or don't have the same underlying cause(s) but not use the term Coanda for the latter phenomenon.

I also point out that in Coanda's earliest US patent, he explicitly includes both forced jets and sheets. US2052869A 1936

Regards, -- Steve -- (talk) 04:17, 12 October 2014 (UTC)

Causes section

An un-authenticated user inserted the following comment into the article:

In the below paragraph the example of spoon seems to be wrong. I am no master in physics, so if any reader is, please check whether the example is correct or not. The example has being contradicted some 10-15 paragraphs below.;-)

This belongs on the talk page, not in the article itself. I'm going to remove the comment. And since I agree that the paragraph is problematic, I'm going to comment out the paragraph until we reach some consensus about what it should say. Mr. Swordfish (talk) 14:44, 25 August 2014 (UTC)

Delving in a bit farther, while it is true that Anderson & Eberhardt (the cited source) ascribe the cause to viscosity, this is not widely supported and another article states that this is a misconception (Lift_(force)#Misconception_regarding_the_role_of_viscosity. I'm removing the section pending consensus. Mr. Swordfish (talk) 15:15, 26 August 2014 (UTC)

Causes

The Coandă effect is a result of the viscosity of fluids. Viscosity leads to a velocity profile for the fluid, creating a boundary layer in which the fluid velocity increases from zero at the surface of an object to the free-stream velocity when the distance from the surface is sufficiently great that its presence is negligible. The resulting adjacent streamlines within this boundary layer travel at different speeds, thus creating shear forces that bend the fluid in the direction of the slower-moving streamlines closer to the surface. A corresponding reaction force is then generated on the object in the direction of the flowing fluid, thus "entraining" it.

The existence of this force can be demonstrated by bringing the base of a spoon held vertically into contact with a downward-flowing stream of water; the spoon experiences a force pulling it towards the fluid flow.

References

The removed section is above. Glrx (talk) 23:35, 11 October 2014 (UTC)

"The Coandă effect is a result of the viscosity" - Isn't part of Coandă also related to the fact as mentioned above, that if flow didn't remain attached (or a vortice formed in the case of a stall) to a convex surface, a vacuum would be created? Some have called this aspect of a flow following a convex surface as "void abhorence" effect. I though this was considered to be part of Coandă effect Rcgldr (talk) 21:12, 28 February 2015 (UTC)

Explanation for ping pong ball in diagonal stream

There's a side article showing a ping ball ball suspended in a diagonal stream, mentioning that Coanda effect is why the ball remains in the stream. It also mentions combined with Magnus effect, but the angle of the stream can be reversed (moving the blow dryer while changing the angle so the ball doesn't move much), and even though the ball is initially spinning the "wrong way", it remains stable, so the primary stabilizing factor is the Coanda effect.

Not mentioned is why Coanda effect stabilizes the ball. The stream diverges outwards as it slows (mass flow conservation, ignoring viscous interaction with surrounding air), so the outer portions of the stream are angled more outwards relative to the direction of the stream than the inner portions of the stream. If the ball gets offset within the stream, then the Coanda effect diversion of the wake due to the difference in outer and inner angles of the stream result in a wake that is diverted outwards, which coexists (Newton third law pair) with an inwards corrective force on the ping pong ball.

Rcgldr (talk) 21:03, 28 February 2015 (UTC)

Two things here (Oct 9 2015 edit email brought me here)

1) The Oct 9/2015 __removal__ of the Magnus effect being apart of Coanda was proper, but reference to Magnus is/could be appropriate at that point since they are closely related (The coanda effect does route 'more' air over the high side resulting centering force similar to Magnus). Magnus is reference later, but could be referred to in this section if done appropriately. Perhaps as preemptive to prevent coupling Magnus to Coanda by a future reader.

1a) The caption says "Spinning" ping-pong ball. This spin, induced as a secondary result of the specific 'imbalance correcting' condition, implies that rotation is part of Coanda as User Rcgldr previously pointed out. I recommend that that word 'spinning' be removed from the caption.

1b) Caption also says "...The ball "sticks" to the lower side of the air stream, which stops the ball from falling down. " This makes no sense since 'sticking' implies it will be 'pulled' toward the bottom (or dragged along with) and implies that suction is a scientific concept. I recommend something more like this:

A (ping pong - optional) ball is held in a diagonal stream of air by the Coandă Effect. The centering force being created by less air following the ball's curve on the [side that the ball drifts off center / lower side - optional choice]."

A caption should only refer to the salient feature being discussed, not secessarily explain it fully, but not poorly summarizing either. I provided two ways to describe which side of the ball is discussed, first because it can be a complex definition (many words) and because in the diagonal situation it is the "lower" side, but for the vertical case there is no lower side. Now, since the image is only diagonal, the word 'lower' is appropiate, though limited to the diagonal case. The other words cover the non-diagonal case which arguably can be omitted for THIS image. Describing the side 'away' from the side the ball moved toward, needs more words, so I picked the 'lower'.

Since this can be a contentious issue. I did not just change the article.

2) RE: User Rcgldr|talk]]) 21:03, 28 February 2015 comment redarding flow divergance. This is far too complex here and I am not sure even relevant. He also does not provide a fully cogent explanation as to why diverging air does anything special. More air (per unit time) is diverted (accelerated) around the curve on one side causing the lowered pressure and increased mass diversion (acceleration, or turning) thus yielding both the net (pressure) force on the ball as well as the necessary Newton-Third-Law "reaction" which is all covered in the article. -- Steve -- (talk) 20:39, 9 October 2015 (UTC)

Candles as an example of the coanda effect

This is a direct quote from the article: "This is a demonstration of the Coandă effect without the presence of any surface. In some sense, the plane of symmetry between the two flows can be thought of as the surface. In actual fact this is not the Coandă Effect in action but is in fact the Atmospheric Press in action as putting two candles close together causes an area of warmth between them which warms the air which then rises - leaving the cooler atmosphere to try fill this partial void and so the flames are forced together."

I feel like there is a contradiction in the first half of this quote, or at least it is poorly worded. I know nothing about this subject, so i won't change it, but somebody who does know something should straighten this out. 75.80.51.211 (talk) 07:07, 13 October 2015 (UTC)

I agree. I have added the "Dubious - discuss" tag at the end of the offending paragraph. See my diff. Dolphin (t) 11:17, 13 October 2015 (UTC)

The text in question is confused and has no cites to back it up. I'm going to remove it pending some more reliable sourcing becoming available. Mr. Swordfish (talk) 21:01, 13 October 2015 (UTC)

Reference #2

Reference #2 "http://www.answers.com/topic/coanda-effect" doesn't appear to link to anywhere useful or relevant — Preceding unsigned comment added by 143.52.53.68 (talk) 14:03, 18 January 2016 (UTC)

Thanks for the heads-up. I've replaced it with a better cite. Mr. Swordfish (talk) 16:22, 18 January 2016 (UTC)

Don't comment out dead links. Search for them on archive.org or tag with {{dead link}}. Link recovered. Glrx (talk) 17:59, 19 January 2016 (UTC)

A FINE INTRO !

It is with great satisfaction that I congratulate the author for starting this article with a truly exemplary thesis statement. I can count on one hand the technical articles in Wiki that have accomplished it. I'm going to use this article as an example of how to start technical articles correctly. Bravo! Pb8bije6a7b6a3w (talk) 15:40, 13 December 2015 (UTC)

Well, I wouldn't want to contradict you on that count. However, it goes to show that even a truly exemplary thesis statement can be factually wrong, references not withstanding, as even the referenced material can be in the wrong. I do not know who first discovered or described this effect. But I do have proof that it was described and published at least two decades before the Coanda patent. I can't proof but I am reasonably sure that Coanda actually read the source. It is described in Otto Lilienthals's book 'Birdflight as the basis of Aviation' published in 1889, section XXV pages 56/57 of the American Aeronautical Archives reprint of 2001. It should still be available for purchase for anyone interested. This book was THE authoritative source in the field worldwide (it was used by the Wright brothers for example). So, I am reasonably sure that anyone seriously interested in aviation at the time would have read it and I think Coanda would fit that description. He was the first to discover this effect? I disagree! — Preceding unsigned comment added by 50.156.57.52 (talk) 04:45, 17 February 2016 (UTC)

The book is online at http://catalog.hathitrust.org/Record/001115085

The article points out Young described the effect 100 years before: Coandă effect#Discovery. Glrx (talk) 22:41, 19 February 2016 (UTC)

Explanation needed for why the Coandă effect occurs.

This is a very interesting article, describing in detail WHEN the Coandă effect can be observed, and harnessed; but there is no mention in the article (or on the Talk Page) WHY it occurs. I do not think that a simple statement that a jet of fluid "will adhere" to a curved surface is a sufficient explanation of the Coandă effect. Why does it adhere to that surface? There should at least be a section of the article which deals with this fundamental problem, regarding the phenomenon. Surely the explanation cannot be terribly difficult or arcane to understand in terms of straight forward physics.

The present article sounds (by analogy) almost as if the orbit of the Moon round the Earth can be explained as a physical "law" unto itself, without reference to gravity and Newton's Laws of motion and inertia (etc., etc.). The Moon (in terms of the way this article is written) orbits the Earth simply because its orbit "adheres" (or "is attached to") to a circular path round the Earth.

Once a proper fundamental physics explanation of why phenomenon occurs is supplied, it will help to resolve many of the questions that have arisen in the article and on the Talk Page on what is, and what is not, the Coandă effect. Cruithne9 (talk) 16:35, 6 November 2016 (UTC)

If there were a good succinct explanation of why the Coandă effect occurs that was published in a reliable source we would be happy to add it to the article. Do you know of one?

I could give my explanation of why it occurs, but that would be original research. Mr. Swordfish (talk) 20:43, 7 November 2016 (UTC)

Hi Mr Swordfish. There is a very good article in Scientific American by Imants Reba, entitled Applications of the Coanda effect, Scientific American, Vol 214(6) June 1966, 84-92. doi:10.1038/scientificamerican0666-84. It provides an explanation for the phenomenon, which you could use if you decide to edit the present article. (I am sure that the explanation in Scientific American will coincide with your explanation - it could hardly be otherwise.)

Although this article was written in 1966, it does not seem that major breakthroughs in the understanding of the phenomenon have occurred since then, other than refining some of the applications. There are many YouTube videos of model airplanes that rely on the Coandă effect for their flying and hovering ability, some of which (unless they have been doctored) look very impressive and promising.

The Scientific American article also provides a story about how Henri Coandă was made aware of the effect that now goes under his name. Even if he did not "discover" the effect, he seems to have been the first to study it in some depth. I think that the present article would be greatly improved if the accident that brought the effect to his attention was included in the history section. It seems odd not to mention how the Coandă effect got its name. Cruithne9 (talk) 08:50, 9 November 2016 (UTC)

I have created the section which describes how the Coanda Effect comes about, as discussed above. Please feel free to improve and expand that section. Cruithne9 (talk) 15:21, 17 November 2016 (UTC).

Can anyone revise the "Conditions for existence" section please?

The Conditions for existence section is very, and unnecessarily technical, as well as being poorly written. I have revised the first half of that section as it simply describes the experiment whose results are depicted in the diagram on the right. But it was clear from that exercise that the reciprocal of the h/r ratio (and not the actual h/r ratios as stated) were quoted both in the original caption to the diagram and in the text. Mistakes like this, plus the poor English, made the section almost incomprehensible. I hope that my rendering of that section has improved matters, even though the diagram to which it refers is unnecessarily complex, having obviously been lifted from a professional journal (or similar text) without the accompanying explanations of what the various codes mean. For instance, what do the water pressure graphs (in cm H₂O - labeled "Cm H²O" in the diagram!) in the top left hand corner of the diagram refer to?

The second half of the section starting with the sentence

A calculation made by L. C. Woods in 1954^[14], of an inviscid flow along a circular wall........ needs serious reworking. Only the people who are already thoroughly familiar with Wood's, Young's, Van Dyke's and Kadosch's work would have the slightest inkling what these paragraphs mean, and whether the "h/r ratios" at the bottom of the section (referring to laminar flow over a curved surface) are true h/r ratios or their reciprocals. Cruithne9 (talk) 08:39, 5 December 2016 (UTC)

Me, me , adsum qui feci!

Sorry for my poor English: I am French (not Latin, don't be afraid: I am 96, still alive). I used the Google Translator. You made corrections of the poor English, and some changes. Thanks for the corrections. As for the changes: your responsibility, of course.

However, you are mistaken concerning h and r. r = rayon in french = radius in english; 1/r = curvature. h = hauteur in french = width in english; h/r = relative curvature

Coanda effect occurs when relative curvature h/r < 0.5, or when r/h > 2: when the radius is large enough.

In my old experiments: r = 120 mm; Coanda effect appeared when h = 40mm, 30mm,20mm,15mm, 10mm It did not appear when h = 60mm and 80 mm, or more of course, but there was not enough room in the lab. By the way, when I refer to a horizontal wall jet along a wall whose radius is the radius of the Earth, I mean a wall jet which could be built as long as desired and remaining without separation because everywhere at the same atmospheric pressure.

Moreover, in your change: "this is a true coanda effect as the jet clings to the wall as in a conventional jet", you omitted to add "at a nearly constant pressure": an essential feature.

Now excuse me again for my poor English: I certain do not adhere at all to the idea that in Coanda effect a jet "adheres" to the curved wall: I put my hands in it and I did not find any glue. Coanda effect is a pure inertial effect as it appears when comparing my calculations after LC Woods (the other figure) and my experiments, the more so as it does not appear at low Reynolds number , it has nothing to do with viscosity,not even a bound vortex, no vortex at all, L.C. Woods said. His work is pure maths, conformal representation of equations of fluid mechanics. My work was pure Excel, just 130 lines, for producing this figure. If you don't mind, I make the convenient changes in the article.Marcel kadosch (talk) 20:21, 14 December 2016 (UTC)

Hi Marcel. Thank you for this response and the changes you have made to the article. It reads much better now than it did before. But I have one small concern. You say that the French hauteur translates into width in English. My very limited knowledge of French, and a beginners' French-English dictionary translates hauteur into height in English. It is crucial in the context of the article which of these two you mean. Could I put it this way: if you mean height then that would refer to the depth of the jet measured from the stationary ambient air through the moving jet of air to the wall; whereas if you mean width then it would refer to the breadth of the jet from side to side as it flows along the wall (i.e. how much of the wall is covered by the jet - a narrow band, or a wide sheet). If the translation of hauteur in your experiments translates into height in English then there is a third possible meaning that makes a major difference to the significance of your results. It could refer to the height or perpendicular distance of the origin of the jet away from the wall! Cruithne9 (talk) 08:45, 15 December 2016 (UTC)

More explanations

I am very happy to see people interested in my experiments 60 years old, published in Journal de Physique, 1958, and also in english in Fluidics Symposium, Washington 1965, and Cambridge (UK) 1967. When I discovered your revision of my contribution, I first wrote this talk in a hurry. I understand that more precision is needed in my report: I shall try to do that in the article as soon as possible. Thanks in advance to any body willing to translate it in understandable english if necessary.

Now I come to your new questions. In all my books and reviews about Coanda effect, including in english Lighthill(1945), Woods(1954), Thwaites (incompressible aerodynamics), Schlichting (boundary layer theory), Bourque and Newman (1960), reviews of fluidics Symposiums (1965, 1967), and also french papers , quoted in references : "w" is used to designate the vertical component of velocity (u,v,w), and not the width of any thing; while "h" is used to designate the width of a two-dimensional channel limited by walls or free jet lines, a suitable model to represent a flow by a figure on a paper.Therefore you should "forget "your french dictionary : "hauteur" is just irrelevant here.

I was surprised to see that more than 60 years after the calculation of Coanda effect by L.C. Woods as a flow of inviscid fluid in a two-dimensional channel limited by walls and jet lines, nobody has tried to make a numerical application, which was impossible in 1954, but straightforward today. The reason is that an inviscid solution exists whatever the deflection angle up to a separation point, and for any given relative curvature h/r. Therefore a consistent calculation implies: either to introduce for a given h/r the separation angle known by the corresponding experiment, and the result is the pressure field to compare with the experimental one, in order to see if they are at least similar, and if it is a true Coanda effect or not; or for the same h/r and experimental separation angle, to use the calculated pressure along the wall for calculating the separation angle of the boundary layer in turbulent flow subject to the condition of this positive pressure gradient, and comparing with the experimental separation angle. I made a first attempt in 1967 to calculate the boudary layer reported in the Cambridge paper without solving the L.C. Woods equation but only an approach of the field pressure. Then I made the job last year with Excel on my computer and obtained the result reported as the figure in the Wikipedia article. Nobody tried before myself, because the existence of my experiments was largely ignored, I presume.

The L.C. WOODS equation of inviscid flow represent inertial effects of the limits of the flow; the influence of viscosity in turbulent flow is negligible, Van Dyke says. anyhow, there is no Coanda effect in laminar flow, nor at low Reynolds numbers, Vit and Marsik say. Inertial effect means effect of the "lateral pressure" as stated by T. Young as soon as in 1800, remember: he deserves it.Marcel kadosch (talk) 23:11, 15 December 2016 (UTC)

Hi Marcel. Thank you very much for this detailed explanation. I am looking forward to the revisions you are planning to make to the article. I'm sure they'll contribute substantially to the encycopedic value of the article.

Rather off the subject under discussion, though peripherally related to your work: what would you imagine would happen if you placed your "wall" (the flat horizontal portion followed by the quarter cylindrical portion, radius 120 mm) in a wind tunnel? That would effectively create an h of infinity. The result would be very interesting, especially if you could conduct the experiment under laminar and turbulent flow conditions (the turbulent flow could be induced by a small lip on the horizontal portion of the "wall". Cheers Cruithne9 (talk) 11:10, 16 December 2016 (UTC)

Good evening: Well, instead of increasing h, why not decrease r? much simpler. Coanda effect depends upon the ratio h/r which must be smaller than 0.5. If h/r>0.5, no more Coanda effect, just local separation at a small angle. With h infinite, the mixing region with atmosphere will disappear, but the boudary layer will remain, separating at a small angle: it will look like the photograph of an aircraft take off. If I could, I should try to remain at constant atmospheric pressure: flat vertical wall, followed by vertical quarter cyndrical wall forming a corner. It happened to me some day, at the end of the Avenue des Champs Elysées, just in front of the Arc de Triomphe: a big gust of wind! Prosperity was not just around the corner, I lost my hat. Coanda? I don't think so.Marcel kadosch (talk) 14:07, 16 December 2016 (UTC)

Good everning Marcel. Nice analogy! Enjoyed chatting to you! Cheers Cruithne9 (talk) 19:20, 16 December 2016 (UTC)

More information about the Coanda effect mechanism

I am writing the revision of my contribution to the article, it should be ready for to-morrow. Meanwhile I must say that I disagree about the image on the left on the preceding section titled : "The Coanda effect mechanism." Image 1 : no low pressure area is created around a free jet , just turbulent mixing with ambient air at ambient pressure, unless ambient environment is closed somewhere, like in image 5, or at least confined, as in image 3 and 4 ; with a smaller space between the jet and the wall at the scale. See : BOURQUE C. and NEWMANN B.C. Reattachment of a two-dimensional incompressible jet to an adjacent Flat Plate in : The Aeronautical Quarterly, volXI, august 1960, pp. 201 and seq. , who displays a thorough study of the phenomenon , both experimental and theoretical . I shall refer to it in my contribution.

In my opinion, in the image on the right on the preceding section, the small step intended to produce a low pressure vortex is not necessary to deviate the jet, but it helps. it should rather act upon the boundary layer.

Finally , I totally disagree with what is said in the last line : deviation occurs in water and in air, but is by no means Coanda effect in water : the image with water is exactly the same as described , with a laser photo, in : C. DUEZ, C. YBERT, L. BOCQUET : Wetting controls separation of inertial flows fom solid surfaces, in : Physical Review Letters, vo. 104, 084503, 2010. A menisk is formed on the wetted surface at the separation point, with a curvature in the opposite direction of what should be supposed to occur with air if anyMarcel kadosch (talk) 16:13, 18 December 2016 (UTC).

diagram request

Just a thought ... wouldn't a diagram for this entry be really useful?

( I just added one. I created it in the GIMP and boy do I hate the bezier tool in that program. Anyone is welcome to clean up my efforts. --Elijah 19:05, 18 May 2006 (UTC) )

Lift

The Coanda effect has nothing to do with the lift over an airfoil! This is a fallacy; lift is entirely produced by circulation (i.e. a bound vortex) and a proper fluid dynamic explanation doesn't need viscosity at all except as an initial condition at the trailing edge (while the Coanda effect is a purely viscous). --Knotnic 00:25, 8 August 2005 (UTC)

removed "The Coanda effect is important in the understanding of an airfoil's lift."

see [3] for a well-written discussion by a physicist and flight-instructor

So you assert that flow-attachment is unimportant in understanding lift? Such a strange position requires a detailed defense, not just an assertion.

So, why do you think that air is deflected from a straight path by the upper airfoil surface? Denker's website on lifting force is otherwise excellent, but the bit about Coanda effect is distorted: it contains both derogatory language as well as a major straw-man fallacy. The trick with the spoon and the jet of water is a very bad illustration of Coanda effect, yet he labels this demonstration as "the Real Coanda effect." No, the real Coanda effect involves flow attachment of gases as well as liquids, so it would require that the water jet take place in an underwater environment... or that the demonstration be performed using a spoon and an air jet in air. The term "Coanda effect" has approximately the same meaning as "flow attachment," so anyone who debunks Coanada effect and applies derogatory labels such as "fairy tale" is essentially trying to debunk (and to attach derogatory lables to) a genuine phenomenon: "flow attachment" in gases. Without flow-attachment, the air flowing above an airfoil would take a relatively straight path (i.e. the airfoil would remain permanently in Stall.)--Wjbeaty 00:47, 30 May 2006 (UTC)

I disagree. You may understand lift in terms of circulation, bound vortex, etc, but the average layman (i.e. the reader of an encyclopedia) probably doesn't, at least at first. It's far more intuitive to talk about lift as a turning of the airflow, creating lift by reaction - that is after all what is happening. The Coanda effect is important in that respect because it explains why the air should stick to the wing surface as it turns. If you read the page on lift, all explanations are given equal weight, and that is right - we need to cater for all audiences, not just aerodynamisicts (what are they doing reading this anyway?). So the statement is right, but might need to be qualified in some way. Graham 00:51, 8 August 2005 (UTC)

Aerodynamisicts are reading this pulling their hair out. Water sticking to the side of an object is in no way related to the lift of an aircraft. This article should be written by people who know aspects of fluid flow at a high level. They should be the ones who simplify the subject for the layman, not laymen themselves. —Preceding unsigned comment added by 74.197.176.46 (talk) 03:37, 19 November 2009 (UTC)

I'm all for alternative explanations when they're equally valid. But the fact remains - you can have lift *without* the Coanda effect. So I don't think it should be given equal weight as an explanation... but am fine for mentioning it as a related fluid phenomenon. I see now that there is extensive discussion on the lift page, so I'll probably not add more here. Knotnic 19:49, 21 August 2005 (UTC)

You mean that we can have lift *without* flow attachment at the upper airfoil surface? But the airfoil would then be well into stall, and only the lower surface would provide significant lift. An explanation of lifting force without Coanda effect (without upper-surface flow attachment) is an explanation of Stall-regime flight, not of normal flight.

Unfortunately the Circulation-based explanation of lifting force makes the unspoken, un-discussed assumption that the flow remains attached to the airfoil surfaces. The turning of an air flow because of flow-attachment is an interesting topic in its own right. I find it odd that anyone would try to debunk it, or try to attach derogatory emotional labels to the concept!--Wjbeaty 19:30, 15 December 2005 (UTC)

The inviscid lift theory works without so-called "flow-attachment", because, if the flow did not remain attached, there would either i) be a vacuum behind the object, or ii) the fluid behind the body would be entrained to "infinity". Neither of these is plausible physically. Even in an inviscid universe, pressure gradients cause fluids to accelerate. The vacuum behind the object would quickly be filled by fluid from the surrounding atmosphere, and lo and behold, there is your boundary layer attachment. Nothing to do with van der Waals forces, electric charges, viscosity, surface tension, or any other type of energy. There is therefore no need for the Coanda effect to explain the lift of an airfoil. Inviscid airfoil theories give surprisingly accurate predictions of lift without taking viscosity into account, provided the airfoil is not stalled. Now drag on the other hand.... Skr777 19:49, 27 June 2007 (UTC)

Coanda effect has significant impact on the lift over an airfoil. It can be applied to control the flow separation which caused by the trailing vortices. Actually the lift is generated by the geometry of the airfoil itself. The type of the airfoil will reflect on how much lift could be generated by the airfoil and this is depending on what is the Reynolds number of the flow. This is applied to either laminar or turbulent flow (turbulent will happen when Re > 500,000). Other consideration is the angle of attack of the airfoil because this will influence the airfoil to become stall or not. At certain angle of attack, there will be turbulent boundary layer at the back of the airfoil which caused by the trailing vortices. At here, the coanda effect could be applied to re-attach back the flow on the airfoil as a method of flow separation control by injection of fluid to the flow. The device that can be used in this case is synthetic jet actuator, which produced oscillatory flow that been injected back to the flow over the airfoil so that the boundary layer will remain laminar. This is what coanda effect deals with the flow over the airfoil. The method said will reduce the drag caused by the trailing vortices and hence, improve the lift!

By definition, the concept of a boundary layer no longer applies to the stalled portion of an airfoil. The turbulence in the wake of a bluff body has nothing to do with boundary layer turbulence. On just about any aircraft larger than a radio-controlled toy, the boundary layer over the wing is always turbulent, except very close to the leading edge. In fact, you may notice longitudinal "ribs" on the suction (upper) surface of commercial aircraft. These are used to intentionally "trip" the boundary layer to a turbulent state during takeoff, when, because of the lower speed (i.e. lower Reynolds number), the transition of the boundary layer to a turbulent state occurs further downstream along the wing. The turbulent boundary layer, because of mixing, has more momentum near the wall, making it less prone to separation due to an adverse pressure gradient (i.e. more stall-resistant).Skr777 19:49, 27 June 2007 (UTC)

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in a vacuum environment with no Coand effect?

No clear Coand what effect was produced. I think Coand effect associated with atmospheric pressure, atmospheric pressure is higher, the more powerful effect Coand. If there is no pressure, no Coand effect. My question is: in a vacuum environment with no Coand effect? The answer must be: no.. Zhgh1912 (talk) 01:08, 31 August 2017 (UTC)

Revisions

Some explication about my revision activity.

I have reinstated some former references, even if in a more concise way. I cannot imagine who introduced the reference to the Kadosch Study which is marginal and full of problem because it is not an experiment that cannot be replicated and then is completely out of the science.It is evident considering the null impact of this experiment on the scientific community (8 citations from 1967 https://scholar.google.it/scholar?hl=en&as_sdt=0%2C5&q=Kadosch+M.%2C+%22The+curved+wall+effect%22&btnG= ) and of secondary importance in terms of results with respect to the ones that follows:

1. Newman, B. G. (1961). The deflection of plane jets by adjacent boundaries—Coanda effect. Boundary layer and flow control, 1, 232-264.

2. Wille, R., & Fernholz, H. (1965). Report on the first European Mechanics Colloquium, on the Coanda effect. Journal of Fluid Mechanics, 23(4), 801-819.

3. Bourque, C., & Newman, B. G. (1960). Reattachment of a two-dimensional, in compressible jet to an adjacent flat plate. The Aeronautical Quarterly, 11(3), 201-232.

In particular the sources are not reported into a linear chronology that presents the evolution of the argument over time while actually they are completely out of any chronological order. Kind regards for the possibility of instating a precise discussion into the specific merit.

In addition the paragraph "Demonstration" has been modified as "Practical Demonstration" because at the moment everyone knows that Coanda effect but no numerical theoretical or analytical method hss produced results that can be generalized. In this direction the former Job done at Unimore in Italt and at Comoti in Romania is the one that ensures the highest number of published replicas even if not general.

Thanks for your attention

George

— Preceding unsigned comment added by Aeronauticengineer67 (talk • contribs) 16:51, 15 March 2018 (UTC)