Moving wall with absolute speed 0m/s vs stationary wall

andyzhu · November 16, 2014, 23:28

Hi,
I'm a little confused by the two sets especially in a frame motion.
The premise is that I used tanslational frame motion to simulate flow passing a ball which is set as a wall with no slip on surface.The thing is:
Case A:
I set the ball with stationary wall.And velocity contour shows the ball does have velocity profile on its surface.
Case B:
I set the ball with moving wall whose absolute speed is 0m/s.And velocity contour shows all the velocity-magnitude on the ball surface is 0.

In my opinion,I think case B is authentic since there's no slip on walls.But on the other side,I think "stationary" shoud equal to"moving wall with absolute speed at 0",what's the difference between case A and case B.

Thank you so much.

LuckyTran · November 18, 2014, 00:46

There shouldn't be any difference. Fluent sets the wall velocityto 0 m/s when you specify stationary wall. What you are doing is the same as what Fluent is doing internally.

andyzhu · November 18, 2014, 05:01

Quote:

Originally Posted by LuckyTran

There shouldn't be any difference. Fluent sets the wall velocityto 0 m/s when you specify stationary wall. What you are doing is the same as what Fluent is doing internally.

Thanks ,Tran.I agree with u.I think the calculated data is the same,while the way it shows differs.

Kokemoor · November 18, 2014, 11:56

If you are using a moving reference frame, stationary walls are always stationary relative to the cell zone. If you are specifying zero absolute velocity in Case B, you will get different results. If you specify zero relative velocity with a moving wall, you should get the same as Case A.

ghost82 · November 18, 2014, 12:26

I agree with Andrew. It's not straightforward, but I remember I read it in ansys' guide.
If you want to specify a fixed wall, always use zero absolute velocity.

andyzhu · November 18, 2014, 21:48

Quote:

Originally Posted by Kokemoor

If you are using a moving reference frame, stationary walls are always stationary relative to the cell zone. If you are specifying zero absolute velocity in Case B, you will get different results. If you specify zero relative velocity with a moving wall, you should get the same as Case A.

Thanks Andrew,I guess "stationary" coincides with the reference whether it moves or not.

cheredha · July 9, 2016, 08:24

hi;
i want create a file profile for piston motion (.prof)

What software should I use it.

thanks;

November 16, 2014, 23:28	Moving wall with absolute speed 0m/s vs stationary wall	#1
andyzhu New Member Yushi Zhu Join Date: Nov 2014 Posts: 6 Rep Power: 12	Hi, I'm a little confused by the two sets especially in a frame motion. The premise is that I used tanslational frame motion to simulate flow passing a ball which is set as a wall with no slip on surface.The thing is: Case A: I set the ball with stationary wall.And velocity contour shows the ball does have velocity profile on its surface. Case B: I set the ball with moving wall whose absolute speed is 0m/s.And velocity contour shows all the velocity-magnitude on the ball surface is 0. In my opinion,I think case B is authentic since there's no slip on walls.But on the other side,I think "stationary" shoud equal to"moving wall with absolute speed at 0",what's the difference between case A and case B. Thank you so much.

November 18, 2014, 12:26		#5
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 27	I agree with Andrew. It's not straightforward, but I remember I read it in ansys' guide. If you want to specify a fixed wall, always use zero absolute velocity. sargordan likes this. __________________ Google is your friend and the same for the search button!

July 9, 2016, 08:24	moving wall	#7
cheredha Member alliche redha Join Date: Jun 2010 Posts: 53 Rep Power: 16	hi; i want create a file profile for piston motion (.prof) What software should I use it. thanks;

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November 18, 2014, 00:46		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	There shouldn't be any difference. Fluent sets the wall velocityto 0 m/s when you specify stationary wall. What you are doing is the same as what Fluent is doing internally.

November 18, 2014, 11:56		#4
Kokemoor Senior Member Andrew Kokemoor Join Date: Aug 2013 Posts: 122 Rep Power: 14	If you are using a moving reference frame, stationary walls are always stationary relative to the cell zone. If you are specifying zero absolute velocity in Case B, you will get different results. If you specify zero relative velocity with a moving wall, you should get the same as Case A.