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Patrick Godon November 5, 2003 16:37

Wall turbulence, viscosity, boundary layer
Hello all,

I would appreciate anyone who could help with either some theoretical remarks or some experiemental insight into the following problem. The problem is originally in astrophysics but it is related to wall turbulence.

The original problem is that of a fluid rotating around the equatorial region of a non-rotating sphere and therefore a boundary layer develops between the sphere and the fluid where they meet. Close enough to the surface of the sphere, where the actual boundary layer begins, one has Re=1, and let us define this distance by (say) Dbl (D for distance and bl for boundary layer). The velocity of the fluid far from the surface is (say) V. The fluid has a given viscosity mu such that nu=rho*nu. In the boundary layer Re=V*Dbl/nu=1. Now the main question is if the turbulence can develop at the contact (wall turubulence ?) and how and why. And if turbulence develops there what happens to the friction? Does the shear between the fluid and the sphere increases or decreases because of the turbulence? and how can one assess the new shear (or the new "effective viscosity" because of the turbulence)? The velocity V can be suppersonic, but the density of the fluid can change so that the velocity might be either subsonic or super sonic. At this stage it is enough if someone only considers a fluid flowing over a flat surface. From the little info I have one expects to have there wall turubulence, however I do not know mucht about that topic (that's why I am posting here).

thanks for any hint.

Patrick Godon November 5, 2003 16:39

sorry for the wrong typing it should be


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