# velocity B.C.

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 December 13, 2000, 08:14 velocity B.C. #1 Pendy Guest   Posts: n/a Hi,everyone, When using staggered grids and the wall is moving(the moving speed is predefined),how to find the u velocity(nearest and parabel to the wall)? pls help me.

 December 13, 2000, 21:31 Re: velocity B.C. #2 frederic felten Guest   Posts: n/a hi there, I assume that the wall that you're talking about is moving in a streamwise direction. If so, the wall movement in this direction (X-direction) is felt by the fluid by a change in the wall shear stress. Its value is adjusted by replacing the velocity Up by the relative velocity Up - Uwall. You still have Vwall= 0.0 and Wwall= 0.0 if the wall is not moving in the wall normal direction and the spanwise direction. i hope this helps, sincerely, Frederic Felten.

 December 13, 2000, 22:58 Re: velocity B.C. #3 Pendy Guest   Posts: n/a thanks there, what you said is right if relative motion can be used,but it cannot work with my study,the predefined velocity of the wall is neither normal nor parallel to the wall,I am now dealing with a flow passing an moving object. Thanks and waiting for help Pendy

 December 14, 2000, 12:19 Re: velocity B.C. #4 Ghanshyam Singh Guest   Posts: n/a I think you are solving a problem of flow past a rotating cylinder. I will do the following: (1) Take very fine grid near the wall. (2) Take velocity of the wall (V=Omega*Radius), deduce normal and tangential components using this velocity. Angle you can obtain using grid line. This again means that first grid point is having the same absolute velocity as that of the wall. Please correct if I am wrong. GS

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