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Calculate Torque from Shear stress in laminar flow 3D

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Hi, I'm trying to calculate the torque on an object that is rotating at steady state inside a fluid. I'd like to check here if I'm doing it right.

I have a 3D model with symmetry in xy plane. Rotation is around the z axis. I added a cylindrical coordinate system (sys2) to easily prescribe the motion as a boundary condition (moving wall) on the surface of the rotating object:
ux = -sin(sys2.phi)*sys2.r*omega
uy = cos(sys2.phi)*sys2.r*omega
uz = 0
(phi is angular coordinate, omega is the rotation rate)
Is this a correct way to prescribe a rotational steady state motion?

The velocity profile looks about right to me. Now to find the torque, I use surface integration on the surface of the rotating body with this expression
2*(spf.T_stressx*y+spf.T_stressy*x)
2* for the symmetry plane, the shear stress/force times the radius for the torque (both x and y components) and finally integrating over the surface to go from stress to force.
It seems to work, but I'm not sure how I can check if the result makes any sense.

0 Replies Last Post 2017年3月2日 GMT-5 17:48
COMSOL Moderator

Hello Stijn van Pelt

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