How to enforce zero velocity along walls of rotating channel?

cfdnewb123 · June 19, 2020, 11:25

I am working on rotating turbulent channel flow and have test it for 2D & 3D. However, I keep getting non-zero velocity for the node point at the wall. This causes a sharp transition from wall surface to fluid flow which is unphysical. The solver works fine when I set rotation to zero and thus, I suspect I may have set my rotation incorrectly.

For my 3D solver, I set periodic boundary conditions along x and z directions. The flow is driven by dP/dx=-1 which is specify in the periodic conditions. To introduce rotation, I set the walls at y=-h & y=h to rotate along the z-axis at -20 rad/s.
I also try using frame motion instead but the result is much worst. I have no idea how to correctly introduce the rotation.

I can't upload the image here and thus, I have add the relevant link.

Without rotation, the velocity profile is alright as both of its ends starts from zero.
https://imgur.com/oyqMzOs

However, with rotation and at a nonzero distance from rotational axis, both ends of the velocity profile is equal to the wall rotational velocity at that point.
https://imgur.com/FdGa5fm

How do I ensure that both ends of the velocity profile starts from zero? According to the paper I am using, the "wall friction velocity is prescribed and kept constant in all numerical computations" and I believe that is the key to my problem. However, I can't seem to explicitly compute the wall friction velocity on Fluent...

vinerm · June 19, 2020, 11:56

You have set walls to be moving, therefore, it is obvious that the velocities at the nodes on the walls are non-zero. If you don't want that, i.e., if the walls are stationary with respect to inertial frame, then you should set their absolute velocity to 0 or their relative velocity equal and opposite to that of cell zone velocity.

cfdnewb123 · June 19, 2020, 12:54

Thanks for the response! I resolved it by manually removing the velocity profile from the imposed wall rotation.

bam28 · August 5, 2020, 05:45

hello cfdnewb123,
Could you please explain in detail how did you solve the problem? I am facing a similar problem. Thank you so much.

June 19, 2020, 11:25	How to enforce zero velocity along walls of rotating channel?	#1
cfdnewb123 Member Join Date: Feb 2019 Posts: 69 Rep Power: 7	I am working on rotating turbulent channel flow and have test it for 2D & 3D. However, I keep getting non-zero velocity for the node point at the wall. This causes a sharp transition from wall surface to fluid flow which is unphysical. The solver works fine when I set rotation to zero and thus, I suspect I may have set my rotation incorrectly. For my 3D solver, I set periodic boundary conditions along x and z directions. The flow is driven by dP/dx=-1 which is specify in the periodic conditions. To introduce rotation, I set the walls at y=-h & y=h to rotate along the z-axis at -20 rad/s. I also try using frame motion instead but the result is much worst. I have no idea how to correctly introduce the rotation. I can't upload the image here and thus, I have add the relevant link. Without rotation, the velocity profile is alright as both of its ends starts from zero. https://imgur.com/oyqMzOs However, with rotation and at a nonzero distance from rotational axis, both ends of the velocity profile is equal to the wall rotational velocity at that point. https://imgur.com/FdGa5fm How do I ensure that both ends of the velocity profile starts from zero? According to the paper I am using, the "wall friction velocity is prescribed and kept constant in all numerical computations" and I believe that is the key to my problem. However, I can't seem to explicitly compute the wall friction velocity on Fluent...

June 19, 2020, 11:56	Wall Motion	#2
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36	You have set walls to be moving, therefore, it is obvious that the velocities at the nodes on the walls are non-zero. If you don't want that, i.e., if the walls are stationary with respect to inertial frame, then you should set their absolute velocity to 0 or their relative velocity equal and opposite to that of cell zone velocity. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

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June 19, 2020, 12:54		#3
cfdnewb123 Member Join Date: Feb 2019 Posts: 69 Rep Power: 7	Thanks for the response! I resolved it by manually removing the velocity profile from the imposed wall rotation.

August 5, 2020, 05:45		#4
bam28 New Member Join Date: Apr 2020 Posts: 3 Rep Power: 6	hello cfdnewb123, Could you please explain in detail how did you solve the problem? I am facing a similar problem. Thank you so much.