If the wing is absolutely smooth and has no friction, will it still generate lift?

Question

I think it will generate lift, because downwash air flow still exists. But I'm not sure if I'm right.

Answer 1

The wing surface itself does not generate friction (though surface roughness does matter). It's the viscosity of the fluid that generates friction. Even a perfectly smooth boundary will experience friction due to no-slip condition. Therefore, you can't have a viscous fluid and a "zero friction surface" simultaneously.

If you assume flow is inviscid, on the other hand, then lift cannot be generated by itself, since an irrotational flow remains irrotational for all time. If you assume flow tangency condition, you will get a unique non-lifting flow solution.

We are able to derive lifting solution in potential flow because we impose an extra Kutta condition at the trailing edge. But the Kutta condition is completely external to potential flow. The actual physical process that results in the Kutta condition is viscosity itself.