How to enforce zero velocity along walls of rotating channel?

cfdnewb123 · June 19, 2020, 10:25

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, 10:56

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, 11:54

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

bam28 · August 5, 2020, 04:45

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, 10:25	How to enforce zero velocity along walls of rotating channel?	#1
cfdnewb123 Member Join Date: Feb 2019 Posts: 65 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, 10:56	Wall Motion	#2
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	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.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Rotating domain vs Wall velocity	Jiricbeng	CFX	16	January 30, 2020 09:06
3D Rotating Channel	Curtin University	FLUENT	5	November 9, 2018 02:25
Velocity profile is not turbulent (OPEN CHANNEL FLOW)	roi247	FLUENT	2	March 15, 2017 07:30
UDF for 3d velocity inlet profile in channel flow	Thejas4ansys	Fluent UDF and Scheme Programming	0	April 1, 2016 15:09
rotating channel	emilio	Siemens	1	April 6, 2012 00:21

June 19, 2020, 11:54		#3
cfdnewb123 Member Join Date: Feb 2019 Posts: 65 Rep Power: 7	Thanks for the response! I resolved it by manually removing the velocity profile from the imposed wall rotation.

August 5, 2020, 04:45		#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.