- #1

- 60

- 0

and is there any mathematical derivation/proof for coanda effect?

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter perfectz
- Start date

- #1

- 60

- 0

and is there any mathematical derivation/proof for coanda effect?

- #2

- 60

- 0

is my question so stupid that no one can answer?

- #3

russ_watters

Mentor

- 21,180

- 7,987

http://en.wikipedia.org/wiki/Coanda_effect

The simplest part of the explanation is that if the flow didn't stay connected to the airfoil, there would be a vacuum, so it is that vacuum that pulls the air down against the airfoil.

- #4

- 60

- 0

dude russ,

I personally feel that coada effect is a function of the velocity of the fluid stream,(in other words rate of shear) and the radius of curvature of the cylinder, spoon, airfoil.

And I am sure that there is much more to the story. Wikipedia doesn't give any mathematical/physical derivation, but explains the physical aspect of it.

So I need some heavy derivations. Is it patented?

I personally feel that coada effect is a function of the velocity of the fluid stream,(in other words rate of shear) and the radius of curvature of the cylinder, spoon, airfoil.

And I am sure that there is much more to the story. Wikipedia doesn't give any mathematical/physical derivation, but explains the physical aspect of it.

So I need some heavy derivations. Is it patented?

Last edited:

- #5

- 178

- 2

For an airfoil with positive angle of attack, the downstream stagnation point will be on top of the airfoil. This is impossible to maintain in a viscous fluid because there would be an infinite change in velocity around the trailing edge of the airfoil. The stagnation point moves to the trailing edge via an induced circulation about the airfoil.

http://en.wikipedia.org/wiki/Kutta_condition

http://en.wikipedia.org/wiki/Circulation_(fluid_dynamics)

theres links to info about the kutta condition and circulation

ive only had one fluid mechanics class so correct me if im wrong on some of these things

- #6

FredGarvin

Science Advisor

- 5,067

- 10

http://jnaudin.free.fr/html/coanda.htm

http://www.phys.ttu.edu/~cmyles/Phys5306/Talks/2004/Fluid Dynamics.ppt

Apparently it was patented at one time:

http://jnaudin.free.fr/files/coanda/US2108652.pdf

- #7

- 60

- 0

so there's no mathematical/scientific derivation for coanda effect?

- #8

- 51

- 0

http://en.wikipedia.org/wiki/Kutta_condition

The Kutta condition is a principle in fluid dynamics, especially aerodynamics, applied at sharp corners such as trailing edges of airfoilsin steady flow. It allows an aerodynamicist to incorporate a significant effect of viscosity while neglecting viscous effects in the underlying conservation of momentum equation. It is important in the practical calculation of lift on a wing.

Besides wing stall, what might be another example of "unsteady flow"?

- #9

- 14

- 0

So, the answer to your question is, the chamber of the aerofoil makes it behave like a venturi, resulting in variation of velocity and pressure. Lower surface of an aerofoil are generally flat.

- #10

- #11

- 3,314

- 998

- #12

- 14

- 0

- #13

- 3,314

- 998

Potential flow theory would show that at positive angle of attack, the rear stagnation point would be on top of the airfoil and that the air on the bottom would bend around the trailing edge and meat the top air at that stagnation point. On an airfoil, which has a sharp trailing edge, that would require an infinite velocity while turning around that edge. In a real, viscous fluid, this is impossible. The viscosity of the fluid essentially forces that rear stagnation point to be located at the trailing edge, meaning the top flow is much faster than the bottom flow in order to satisfy continuity.

That is the real cause of the flow over the top of the foil being so much faster than below. The higher speeds means that the airfoil has a net circulation when at steady-state, and that circulation can translate into lift through the Kutta-Jukowski theorem. You could also just take the actual velocity profile and do Bernoulli on it.

The important thing is that the Kutta condition is exactly what explains the accelerated flow over the top of the airfoil. Of course, I would love to hear your competing argument for why it

- #14

- 14

- 0

Ok, as per BONEH3AD statement, once the stagnation point is relocated at trailing edge, the job is done, and air should stop accelerating. But this is not the actual case. Kutta condition just explains circulation and starting vortices. This no where explains why air flows faster on upper surface.

- #15

- 3,314

- 998

You still haven't explained adequately how I am wrong. That, of course, is because I am not wrong.

- #16

gmax137

Science Advisor

- 2,039

- 1,482

You are seriously going to argue this? I do aerodynamics for a living.

I don't know if you're right or not, but this kind of appeal to authority just doesn't cut it here. Nobody is really interested in what you do for a living.

- #17

- 3,314

- 998

- #18

- 563

- 2

I don't know if you're right or not, but this kind of appeal to authority just doesn't cut it here. Nobody is really interested in what you do for a living.

It gets my attention.

- #19

- 28

- 0

http://arxiv.org/abs/nlin/0507032

- #20

- 28

- 0

You're confusing cause and effect. The Kutta condition is an effect. The phenomenon is air molecules flowing by and interacting with the molecular structure of an airfoil.

For an airfoil with positive angle of attack, the downstream stagnation point will be on top of the airfoil. This is impossible to maintain in a viscous fluid because there would be an infinite change in velocity around the trailing edge of the airfoil. The stagnation point moves to the trailing edge via an induced circulation about the airfoil.

http://en.wikipedia.org/wiki/Kutta_condition

http://en.wikipedia.org/wiki/Circulation_(fluid_dynamics)

theres links to info about the kutta condition and circulation

ive only had one fluid mechanics class so correct me if im wrong on some of these things

http://arxiv.org/abs/nlin/0507032

- #21

- 40

- 0

- #22

- 12

- 0

You're confusing cause and effect. The Kutta condition is an effect. The phenomenon is air molecules flowing by and interacting with the molecular structure of an airfoil.

http://arxiv.org/abs/nlin/0507032

It's been a while so forgive me if there are inconsistencies in this but I believe ccrummer is correct. Kutta is based on circulation and if I remember correctly, circulation originates from viscous effects and boundary conditions on the airfoil. This being the case, the flow must bend to create a transition region of some sort behind the camber causing a low pressure region speeding up the original flow.

- #23

- 40

- 0

- #24

- 14

- 0

Firstly, kutta condition is not a cause for air flowing at a greater speed over the airfoil. It is an effect of it.

The cause comes from the fact that airfoil in air, behaves like half venturi tube, which can explain all the features of the airfoil.

It can explain why air flow is faster on the upper surface

It can explain the developement of adverse pressure gradient

This assumption can also help in explaining the airfoil behaviour in supersonic flow as well

I dont know how to add figures in this space, to explain.

This assumption of half venturi tube can explain everything of airfoil, without any trace of doubts.

I knw some people are not in agreement of the term HALF VENTURI TUBE, i am ready for criticism.

- #25

- 14

- 0

Share: