I am calculating fluid domain with one inlet and two outlets (fig.1)
I found that Ansys CFX unable to determine how much mass flow rate go to each outlet if i use boundary conditions: Total Temperature and Total Pressure at the Inlet and Mass Flow Rate at the all Outlets. On the fig.2 shown how mass flow rateat the outlets are changing during calculations, you can see that mass flow rate cannot stabilize. It is means that Ansys CFX solver cannot find how much mass flow rate go to each outlet.
If i use boundary conditions: Total Temperature and Total Pressure at the inlet and I define two mass flow rate, for each outlet, Ansys CFX easily findthe solution (fig. 2, fig.3).
The problem is that as i think defining in the boundary conditions how much mass flow rate go to each outlet is strong assumption.
Please tell me how i can define how much mass flow rate go to each outlet by calculating in Ansys CFX?
you can use the boundary condition of this case, the velocity at inlet and pressure at the outlet for a tow outlet.
the mass flow rate depend on the geometry dimensions.
In my opinion, for incompressible flows, fixing the two flow rate at the outlets makes physical sense only for symmetric geometry and steady state. Otherwise the solution at the outlet should depend on the pressure loss due to dissipation in the channels and the flow rate should accomodate according to the solution.
Have you tried to prescribe only static pressure at the outlets?
Filippo Maria Denaro Santosh Kumar Singh Manigandan Sekar thanks for your answers. I am calculating compressible fluid (Water Ideal Gas). I cannot define static pressure at the outlet because i don't know value of static pressure at the outlet.
I try use another model. I create additional pipeline to do one outlet (fig.1). I use Total Temperature and Total Pressure boundary conditions at the inlet and Mass Flow at the outlet. In this case CFX solver successfully got the solution and mass flow rate at the each pipeline are stabilized (fig.2, fig.3)
What are you think about additional pipeline ? Is it physically right to create additional pipeline for creating one outlet ?
In case of two outlet surfaces you cannot be sure how the inlet flow case would distribute. It depends on the geometry and on the pressure exit conditions. In your case, your geometry is not symmetric and you cannot divide the inlet flow rate in two equal outlet. The best thing would be assume atmospheric static pressure at the outlet. Adding a supplementary channel resolves correctly the CFD setting but the solution can be very different from your initial case.
Filippo Maria Denaro I have done calculation with boundary conditions your suggested (atmospheric static pressure at the outlet). In this case CFX solver easily find solution ,all parameters are stabilized (including Mass FLow Rate in each pipe). But it turns that mass flow rate came bigger that i want .
I think if i will do many calculations with variable static pressure at the outlet i will finally get the solution and this solution will be the same as in case when i make addtional pipeline.
What do you think about it ? Can there any problems if I use model with additional pipelines instead series of calculations with variable static pressure?( I think it will be reasonable to use model with additional pipeline, because CFX domen may be more harder and one calculations must require a lot of time).
If you have to model a real device try to simulate while matching the physical conditions.
you can use the boundary condition of this case, the velocity at inlet and pressure at the outlet for a tow outlet.
the mass flow rate depend on the geometry dimensions.
Dear Vladimir
I would suggest to use the attached file exploring good example about your request (Exhaust manifold as a Tutorial).
Regards
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