Boundary conditions required - Couette flow

Thuyavan.Subramani · April 23, 2015, 10:40

Hello all,

I want to simulate laminar flow with fully filled fluid water and observe pressure distribution in it. The change in pressure will take place mainly due to the its geometry shape of top wall (moving) and bottom wall (stationary). To observe that, few mandatory boundary condition has to be set. That is, the pressure value on the inlet and outlet side should be same. The top wall will be moving with some velocities and the bottom plate is stationary.

I tried with different setting conditions for inlet and outlet (1.Inlet/outlet 2. Opening-both end. 3. Opening condition on inlet side and Outlet condition on outlet side) along with moving top wall to run simulation. But, I am getting the error (refer image 3). I considered Ansys solver recommended suggestion, but still I am getting the same error.

I am able to run simulation only by setting boundary condition with inlet (normal speed) and outlet (avg. Static press 0), where both top and bottom wall - STATIONARY.

Requesting to suggest suitable boundary condition for my problem and also on which parameter should I focus?

Thanks in advance
Thuyavan.Subramani.

Opaque · April 23, 2015, 11:13

You cannot use a moving wall boundary condition using a velocity with non-zero normal component without deforming the mesh. It is physically impossible.

The spherical part of the wall pushes the mesh towards one side; therefore, intruding into the domain.

Take a look a mesh deformation modeling in order to complete your simulation.

evcelica · April 23, 2015, 17:13

Hmm, It seems to me you may be able to move the other walls, (not the one with the sphere.) Then adjust your inlet velocity to match your new frame of reference, which is now the sphere wall. It's the relative movement of everything that matters.

Pressure cant be the same on the inlet and outlet, since the fluid would not flow without a pressure difference.

Thuyavan.Subramani · April 24, 2015, 05:11

Thanks a lot both of you for the reply. Mr. Opaque is right, now the simulation is running without any error. Mr. Erik, my focus was to observe more velocity and pressure change, between the regions of those two sphere (as the gap is reduced due to the movement of top wall). To observe exact increase of those parameter, I am trying to maintain same pressure on the inlet and outlet side and also created two domain (left and right). I have not come across with the concept of reference of frame. Anyway, I will look into help file now. If I am not clear, will get back to you.

Once again thanks to both of you.

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April 23, 2015, 11:13		#2
Opaque Senior Member Join Date: Jun 2009 Posts: 1,800 Rep Power: 32	You cannot use a moving wall boundary condition using a velocity with non-zero normal component without deforming the mesh. It is physically impossible. The spherical part of the wall pushes the mesh towards one side; therefore, intruding into the domain. Take a look a mesh deformation modeling in order to complete your simulation.

April 23, 2015, 17:13		#3
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,167 Rep Power: 23	Hmm, It seems to me you may be able to move the other walls, (not the one with the sphere.) Then adjust your inlet velocity to match your new frame of reference, which is now the sphere wall. It's the relative movement of everything that matters. Pressure cant be the same on the inlet and outlet, since the fluid would not flow without a pressure difference.

April 24, 2015, 05:11		#4
Thuyavan.Subramani New Member Thuyavan.Subramani Join Date: Feb 2015 Posts: 4 Rep Power: 11	Thanks a lot both of you for the reply. Mr. Opaque is right, now the simulation is running without any error. Mr. Erik, my focus was to observe more velocity and pressure change, between the regions of those two sphere (as the gap is reduced due to the movement of top wall). To observe exact increase of those parameter, I am trying to maintain same pressure on the inlet and outlet side and also created two domain (left and right). I have not come across with the concept of reference of frame. Anyway, I will look into help file now. If I am not clear, will get back to you. Once again thanks to both of you.