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-   -   Specifying more constranits on Inlet bcs (https://www.cfd-online.com/Forums/cfx/18581-specifying-more-constranits-inlet-bcs.html)

 kvbswamy July 17, 2001 02:22

Specifying more constranits on Inlet bcs

Hi all, I am solving a compressible flow problem where I have multiple inlets(5) with one outlet. I use the total pressure and static temperature specified at inlet and mass specified at the outlet. With this I get overall mass flow as I expected but the mass flow thru each inlet is different from the value I expect. How to rectify this problem ? Thanks for your time Veera

 Herve July 17, 2001 05:10

Re: Specifying more constranits on Inlet bcs

Could you be more specific, give more details?

Herve

 kvbswamy July 17, 2001 07:40

Re: Specifying more constranits on Inlet bcs

Hi,

At each inlet region I have different Total Pressure and Static Temperature specified. For the outlet I have specified the total mass flow.

After the analysis I find that the mass flow through each inlet does not match the mass flow rates I have. Is there a way specify Total pressure and mass flow rate at the inlet.

 Robin Steed July 17, 2001 15:22

Re: Specifying more constranits on Inlet bcs

Hi Veera,

Is there a way specify Total pressure and mass flow rate at the inlet?

You cannot specify total pressure and mass flow at a boundary. If you were to do so, the problem would be over-specified. If you specify total pressure, the flow downstream of your inlet will determine the mass flow rate, as it should in the real physical situation. Alternatively, if you specify a mass flow rate at your inlet, the total pressure will come out of the solution.

When setting up your problem, choose a boundary condition which reasonably approximates the flow conditions at that boundary, based on what you know or expect. If you are certain you have a specific mass flow rate, then a mass flow specified b.c. is appropriate. If your solution is different than you expected you may review your assumptions, verify that you have sufficiently defined your geometry, and check that you have built a reasonable grid.

With this I get overall mass flow as I expected...

CFX-TASCflow and CFX-5 are conservative codes, so unless you have not converged your solution, or you are running a transient compressible simulation, the mass flow into the domain will equal the mass flow out.

Best regards,
Robin
http://www.cfx.aeat.com/

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