[OcQue]

Hi everyone,

I'm trying to simulate Coutte flow. First I created a rectangular surface of 20x1 cm, then I set the boundary condition for the front and back lines as periodic, lower line as no-slip stationary wall, and upper line as moving wall at 0.1 m/s. The used fluid was liquid water. I don't know why I got the result for the pressure field like below, which, theoretically, is supposed to be constant.

couette pressure.PNG

I'm new to CFD, so please kindly help. Thanks a lot!

[Leonardo.flores]

Try pressure inlet and outlet = 0 Pa. Also, what is your mesh resolution?

[LuckyTran]

Would be nice to see the colorbar scale to see if it is even a significant change in pressure.

And does the velocity make sense and look like the theoretical solution? If no, then there's no way the pressure contour will make sense. Remember pressure is whatever it needs to be to satisfy the constraints on the problem. So first check a more relevant parameter like velocity.

[OcQue]

Originally Posted by Leonardo.flores

Try pressure inlet and outlet = 0 Pa. Also, what is your mesh resolution?

Thanks Leonardo for your suggestion. But this is exactly one of ways I tried in the first place and I got a wierd flow result. My mesh is 100x10. Is this a good mesh for such a flow?

[OcQue]

Originally Posted by LuckyTran

Would be nice to see the colorbar scale to see if it is even a significant change in pressure.

And does the velocity make sense and look like the theoretical solution? If no, then there's no way the pressure contour will make sense. Remember pressure is whatever it needs to be to satisfy the constraints on the problem. So first check a more relevant parameter like velocity.

Thanks for your reply, Tran.

The velocity is like the theoretical solution. The pressure difference is 1.4 Pa. How can I tell whether it is significant or not?

couette pressure.PNG

[Leonardo.flores]

As I can see in the colorbar you have a range from -8e-10 to 6e-10 Pa. That can be considered as a zero constant pressure. So those fluctuations in the field could be numerical errors then!
Just deactivate the automatic data range and define a wider range. The field should become constant then.

[OcQue]

Originally Posted by Leonardo.flores

As I can see in the colorbar you have a range from -8e-10 to 6e-10 Pa. That can be considered as a zero constant pressure. So those fluctuations in the field could be numerical errors then!
Just deactivate the automatic data range and define a wider range. The field should become constant then.

Ah my bad! I have no idea why I misread the range of e-10 as e-2. It's solved now. Thanks again for your help