UrgentPressure Inlet Bundary Condition ErrorUrgent

golriz · August 23, 2010, 14:16

Dear all
I have a question about reversed flow error in pressure inlet boundary condition. I am modeling flow of water in a simple channel (only one faze). I have 4 boundary conditions, velocity inlet, pressure inlet for free surface, wall and pressure outlet for outlet. I know that I can use symmetry boundary instead of pressure inlet for free surface, but I want to know why the results of velocity filed of these two cases are different each others?
Let me to ask my question in another way, can I use pressure-inlet boundary condition for free surface of water or not? If I can please explain for me why the flow is reversed and how I can fix this error?
I hope some nice persons help me.
Best Regards,
Farhad

xrs333 · August 23, 2010, 22:17

Hi, Farhad,
Free surface can not be simulated by pressure inlet. A problem fall into the category of open channel flow, a multiphase flow, if it involves free surface of two phases. In FLUENT, VOF model can be used for this.

golriz · August 24, 2010, 14:50

Hi Xrs333
Thanks a lot for your reply.
According to your reply I mention some points and questions, please answer them:

1- I know that the VOF model can model free surface, but I do not want to model the free surface. I want modeling only region under free surface. The interface of two faze is not important for me (My free surface has not any fluctuation).

2- In fact I want to model the sedimentation in a sedimentation tank (settling tank). I have mixture of water and sand in a tank and there is a free surface at above. My main problem is that which boundary conditions must be applied for it? Is pressure inlet done?

3- Can I use Eulerian model for 3 faze (water, sand and air) or must be used a two faze model and a boundary conditions for free surface?

4- Is it possible using pressure inlet for free surface and 2 faze instead of modeling 3 faze in Eulerian model?

And Finally
5- Is Eulerian model able to predict the interface of water and air or the VOF model is the single model for this target?
Best Pleasure,

xrs333 · August 24, 2010, 20:53

In this case wall boudary with zero shear stress can be used to simulate free surface. As to the Eulerian multiphase model I am not familiar with it.

golriz · August 25, 2010, 03:36

Thanks Xrs333.

August 23, 2010, 14:16	**UrgentPressure Inlet Bundary Condition ErrorUrgent**	#1
golriz Member farhad Join Date: Mar 2010 Location: Tehran Posts: 32 Rep Power: 16	Dear all I have a question about reversed flow error in pressure inlet boundary condition. I am modeling flow of water in a simple channel (only one faze). I have 4 boundary conditions, velocity inlet, pressure inlet for free surface, wall and pressure outlet for outlet. I know that I can use symmetry boundary instead of pressure inlet for free surface, but I want to know why the results of velocity filed of these two cases are different each others? Let me to ask my question in another way, can I use pressure-inlet boundary condition for free surface of water or not? If I can please explain for me why the flow is reversed and how I can fix this error? I hope some nice persons help me. Best Regards, Farhad

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August 23, 2010, 22:17		#2
xrs333 Senior Member xrs333 Join Date: Aug 2010 Posts: 125 Rep Power: 16	Hi, Farhad, Free surface can not be simulated by pressure inlet. A problem fall into the category of open channel flow, a multiphase flow, if it involves free surface of two phases. In FLUENT, VOF model can be used for this.

August 24, 2010, 14:50		#3
golriz Member farhad Join Date: Mar 2010 Location: Tehran Posts: 32 Rep Power: 16	Hi Xrs333 Thanks a lot for your reply. According to your reply I mention some points and questions, please answer them: 1- I know that the VOF model can model free surface, but I do not want to model the free surface. I want modeling only region under free surface. The interface of two faze is not important for me (My free surface has not any fluctuation). 2- In fact I want to model the sedimentation in a sedimentation tank (settling tank). I have mixture of water and sand in a tank and there is a free surface at above. My main problem is that which boundary conditions must be applied for it? Is pressure inlet done? 3- Can I use Eulerian model for 3 faze (water, sand and air) or must be used a two faze model and a boundary conditions for free surface? 4- Is it possible using pressure inlet for free surface and 2 faze instead of modeling 3 faze in Eulerian model? And Finally 5- Is Eulerian model able to predict the interface of water and air or the VOF model is the single model for this target? Best Pleasure,

August 24, 2010, 20:53		#4
xrs333 Senior Member xrs333 Join Date: Aug 2010 Posts: 125 Rep Power: 16	In this case wall boudary with zero shear stress can be used to simulate free surface. As to the Eulerian multiphase model I am not familiar with it.

August 25, 2010, 03:36		#5
golriz Member farhad Join Date: Mar 2010 Location: Tehran Posts: 32 Rep Power: 16	Thanks Xrs333.

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UrgentPressure Inlet Bundary Condition ErrorUrgent