# Coanda profile

1. May 2, 2007

### Shridhar .S

Can some one spread more light on coanda profile its effects ,calculations etc

2. May 14, 2008

### ccrummer

The Coanda effect in air is the fact 1) a smoke stream in a wind tunnel follows a surface that gently curves away from the direction of the flow and 2) air from the main flow is entrained to follow the surface. It is caused by the reduced pressure at the surface. Why is the pressure reduced there? Because the interaction of the flow with the static particles in the boundary layer of the surface blows particles away from the surface. Fewer particles, lower pressure. If the Coanda effect could be used to reduce the pressure at the surface to 0 (a VERY ambitious task), there would remain 14.7psi pressure on the other side of the body. A VERY large pressure. To exploite the Coanda effect is to manage buoyancy.

3. May 14, 2008

### ccrummer

Coanda effect

Some people conflate the Coanda effect and effects covered by Bernoulli's equation (a statement of the conservation of energy). Because the Coanda effect is caused by the shearing, unsteady flow near a surface, Bernoulli's equation doesn't hold. (See Landau & Lif****z "Fluid Mechanics" and read carefully the section on the Bernoulli equation.) Beware, this topic is very sensitive and rhetoric waxes religious in its fervor. There is nothing magic about the Coanda effect. It is well-known, so its existence isn't in question. Its explanation is, however. Hint: it is caused by the interaction of fluid particles with each other and with the surface. Bernoulli's equation assumes no such interactions.