According to wikipedia "The onset of turbulence can be predicted by the Reynolds number, which is the ratio of inertial forces to viscous forces within a fluid which is subject to relative internal movement due to different fluid velocities, in what is known as a boundary layer in the case of a bounding surface such as the interior of a pipe". I might be misunderstanding, but one takeaway from this is that if there was no boundary layer around an hypothetical object (i.e. it would repell air molecules), then there would be no velocity difference between the layers of air and consequently no turbulenece. Is that correct? Is the velocity difference between the "layers" of air the cause for turbulence?