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set rotating boundary condition in 3D annulus flow

Posted 9 mai 2019, 17:02 UTC−4 Computational Fluid Dynamics (CFD) Version 5.4 2 Replies

Chunlou Li
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Dear all, I'm kind of new user of Comsol. Any suggestion will be appreciated regarding to my question. I want to model fluid flow in annulus (between two cylinders) with the inter cyliner rotating with a given speed. The 2 ends of the annulus are the inlet and outlet. With either 5.4 or 5.3, I cannot find where to set that wall condition. The options under "moving wall" include "sliding wall" and "moving wall", but no "rotating wall". Somebody can point me to the right direction? thank you very much.

Chunlou

2 Replies Last Post 10 mai 2019, 08:29 UTC−4
Alexis Prel
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Posted: 6 years ago 10 mai 2019, 08:27 UTC−4
Updated: 6 years ago 10 mai 2019, 08:28 UTC−4

I am not familiar with the fluid flow modules, but in the moving wall condition, is it not possible to specify a vector expression for the wall's velocity?

If the above is possible, then you could input the local instaneous velocity as a function of spatial coordinates. So for a point such that is equal to the inner cylinder's radius, I would expect this velocity assuming a constant pulsation

where the sign of determines whether the rotation is clockwise or counter-clockwise.

Note that I assumed that the axis is both the axis of symmetry and the axis of rotation of the inner cylinder. You have to tinker a little bit if your origin is different.

I am not familiar with the fluid flow modules, but in the `moving wall` condition, is it not possible to specify a vector expression for the wall's velocity? If the above is possible, then you could input the local instaneous velocity as a function of spatial coordinates. So for a point P=(x_P, y_P, z_P) = (r_P, \theta_P, z_P) such that r_P is equal to the inner cylinder's radius, I would expect this velocity assuming a constant pulsation \omega ||\vec v|| = r_P |\omega| v_x = \sin(\theta_P) \cdot r_P \cdot \omega v_y = - \cos(\theta_P) \cdot r_P \cdot \omega v_z = 0 where the sign of \omega determines whether the rotation is clockwise or counter-clockwise. Note that I assumed that the axis (x, y, z) = (0, 0, z) is both the axis of symmetry and the axis of rotation of the inner cylinder. You have to tinker a little bit if your origin is different.
Alexis Prel
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Posted: 6 years ago 10 mai 2019, 08:29 UTC−4

Actually, I just realized that the pulsation ω needs not to be constant for this to work.

Actually, I just realized that the pulsation ω needs not to be constant for this to work.

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