Coanda effect

[username]

Did some research on the net and found most information saying it is caused by viscosity and friction, I can understand that in stuff like water but I cant really see how that would hold true for air, could somebody explain it to me or point me to a definitive explanation of the effect?

[Tyger]

which gases display too. The viscosity of a gas is (almost) independent of the pressure, which is why they are compressed for sending through piplelines. J. C. Maxwell first proved that fact.

[ccrummer]

Airfoil lift is caused by a pressure differential between the top and bottom of the airfoil. There are various ways to accomplish this but they fall into two basic classes: 1) increasing the pressure on the bottom of the airfoil, and 2) decreasing the pressure on the top of the airfoil. The Coanda effect is produced as a result of the second. As the viscous air shears past the stationary boundary layer of a surface curving away from the main flow, the pressure at the surface drops and a smoke streamer is "attracted" toward the surface. I have a paper on ArXiV that may shed some light on this. http://arxiv.org/abs/nlin.CD/0507032 . Beware mathematical models that assume zero viscosity for air. That assumption may be valid under some conditions but not when the flow is moving past a surface. Read about "steady" flow and the Navier-Stokes equations, Bernoulli's equation. The concepts are subtle but very interesting. A good reference is Fluid Dynamics by Landau and Lifshitz.