This is wrong. The Coanda effect is about fluid jets; this is how blown flaps work. However an airfoil is in a free-moving fluid not a jet.
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A complete mathematical modeling of lift from first-principles is essentially impossible, as the most straightforward method would likely be Navier-Stokes. That, however, has serious issues with turbulent flow, which will happen somewhere IIRC it becomes quite inaccurate in stall conditions.
It's been a long while since I've done any physics, but my recollection is the practical way to model it is to use Navier-Stokes along with empirically determined approximations of turbulence.
[edit2] A quick reading of the wikipedia article tells me that was mostly right, but NS doesn't have the stall issues, it's the Euler equations (which is a simplified form of NS).
The Navier-Stokes have no problem with stall. The problem is that the Navier-Stokes equations are hard to solve (to use them predictively). The Euler equations do not account for turbulence at all. The Euler equations are good at modeling pressure, which is good for lift and shocks, but does not predict drag, and does a bad job when stall occurs. The RANS equations (a simplified form of the Navier-Stokes equations), do account for tubulence, but one needs a good turbulence model. No turbulence model handles stall well on a broad spectrum of cases, but the RANS equations do do pretty well for attached boundary layers (loosely, when shapes are "aerodynamic" -- like an airplane rather than like a truck or sphere).
It is interesting that the experiment he proposes actually does use a jet of air!
I guess the best counterexample would be to have an airfoil with 0 angle of attack - horizontal on the bottom and curved down on top. Can this wing divert the stream of air downwards, generating enough to allow flight? Even if it does, how much extra lift do you get when you increase the angle of attack?
Yes, please excuse my ignorance of the technical use of the terms.
It would be interesting to see an experiment that isolated any divergence of the airstream caused by Coanda-like effects. I don't know what that experiment would look like, nor if any lift at all would be generated.
Comments
This is wrong. The Coanda effect is about fluid jets; this is how blown flaps work. However an airfoil is in a free-moving fluid not a jet.
[edit] A complete mathematical modeling of lift from first-principles is essentially impossible, as the most straightforward method would likely be Navier-Stokes. That, however, has serious issues with turbulent flow, which will happen somewhere IIRC it becomes quite inaccurate in stall conditions.
It's been a long while since I've done any physics, but my recollection is the practical way to model it is to use Navier-Stokes along with empirically determined approximations of turbulence.
[edit2] A quick reading of the wikipedia article tells me that was mostly right, but NS doesn't have the stall issues, it's the Euler equations (which is a simplified form of NS).
The Navier-Stokes have no problem with stall. The problem is that the Navier-Stokes equations are hard to solve (to use them predictively). The Euler equations do not account for turbulence at all. The Euler equations are good at modeling pressure, which is good for lift and shocks, but does not predict drag, and does a bad job when stall occurs. The RANS equations (a simplified form of the Navier-Stokes equations), do account for tubulence, but one needs a good turbulence model. No turbulence model handles stall well on a broad spectrum of cases, but the RANS equations do do pretty well for attached boundary layers (loosely, when shapes are "aerodynamic" -- like an airplane rather than like a truck or sphere).
It is interesting that the experiment he proposes actually does use a jet of air!
I guess the best counterexample would be to have an airfoil with 0 angle of attack - horizontal on the bottom and curved down on top. Can this wing divert the stream of air downwards, generating enough to allow flight? Even if it does, how much extra lift do you get when you increase the angle of attack?
For an asymmetric airfoil, zero angle of attack is defined as the AoA that produces zero lift.
Yes, please excuse my ignorance of the technical use of the terms.
It would be interesting to see an experiment that isolated any divergence of the airstream caused by Coanda-like effects. I don't know what that experiment would look like, nor if any lift at all would be generated.
It's not a hard experiment to do: make an airfoil out of cardboard and stick it in front of a fan.
That would have no coanda effect though, right? I want an experiment that has only coanda (or similar) effects in play.
Why not?
I've seen it defined as the chordline being parallel to the flow.
Yeah, you can define it that way too. But that's not a very useful definition when you're actually flying an airplane.