Discussion Forum

Hi,

I have been working on the hydrodynamics of a rotating cylinder but I noticed that for Comsol, the "No Slip condition" for a "Sliding Wall" is understood as "A no slip wall is a wall where the fluid velocity relative to the wall velocity is zero".

My point is that when plotting the 3D model: - Flow lines seem consistent - Velocity vectors seem consistent (it is rotating as expected) - Maximum velocity value seem to be halved

I have checked some literature and seems that it is usual, but i cannot get why it is like that. The way I am describing the movement of the cylinder on the xy plane as:

Ux = +/- sqrt((omega * 2 * pi * r)^2/2) Uy = +/- sqrt((omega * 2 * pi * r)^2/2) Uz = 0

where omega is the rotating speed in frecuency units (1/s). As Ux=Uy where x=y, I understand is applying the magnitude of the U vector at every point of the domain, as the COMSOL manual states. I have done it that way to describe the plane and the module of the velocity vector applied at every point of the domain.

if the tangencial velocity of the cylinder surface is 1 m/s, why the maximum velocity of the fluid in contact with the "conveyor belt surface" is around 0.5 m/s?

I have tried doing it with cylindric coordinates describing a 2D axisymmetric component but the "conveyor belt rotation" moves in the z axis direction instead of the "phi" one. The result for the velocity in contact with the cylinder is the same.