boundary condition for define_grid_motion

bongo · August 11, 2009, 11:31

Hi,

I am messing around with deformable grids as I am trying to simulate a system with a moving boundary. I believe that I need to use DEFINE_GRID_MOTION as the nodes on my boundary move relative to one another. I have check the tutorial and managed to run a test case with the wall moving with each time-step. However, I am a little concerned. I have set the coordinates of each node using NODE_COORD(v) and nothing else. If the wall is moving with a certain velocity, then should this velocity not be imparting momentum on the fluid? Can fluent calculate the velocity of the wall based on the time step and change of the nodes co-ordinate?

I have performed a similar simulation using DEFINE_CG_MOTION and set the velocity of the moving wall explicitly.

I am certain that fluent needs a wall velocity for a moving wall to set the correct boundary condition. Has anyone any thoughts?

benjamin_ · June 12, 2013, 04:37

Hi Bongo,

I'm currently experiencing the same issue :

DEFINE_GRID_MOTION on a cell block , for the mesh movement it's OK , but I've a 0 velocity on the moving wall , so a wrong shear stress...

Did you solve this at this time (4years ago...)?

Regards

Ben

August 11, 2009, 11:31	boundary condition for define_grid_motion	#1
bongo New Member Join Date: Aug 2009 Posts: 1 Rep Power: 0	Hi, I am messing around with deformable grids as I am trying to simulate a system with a moving boundary. I believe that I need to use DEFINE_GRID_MOTION as the nodes on my boundary move relative to one another. I have check the tutorial and managed to run a test case with the wall moving with each time-step. However, I am a little concerned. I have set the coordinates of each node using NODE_COORD(v) and nothing else. If the wall is moving with a certain velocity, then should this velocity not be imparting momentum on the fluid? Can fluent calculate the velocity of the wall based on the time step and change of the nodes co-ordinate? I have performed a similar simulation using DEFINE_CG_MOTION and set the velocity of the moving wall explicitly. I am certain that fluent needs a wall velocity for a moving wall to set the correct boundary condition. Has anyone any thoughts?

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June 12, 2013, 04:37		#2
benjamin_ New Member Join Date: Nov 2012 Posts: 6 Rep Power: 14	Hi Bongo, I'm currently experiencing the same issue : DEFINE_GRID_MOTION on a cell block , for the mesh movement it's OK , but I've a 0 velocity on the moving wall , so a wrong shear stress... Did you solve this at this time (4years ago...)? Regards Ben