Target Mass Flow Rate
 

Hello Everybody,

I am simulating compressible flow in 90 degree bend with an extension tube at the bend exit. I need to use total pressure at the inlet and mass flow rate at the exit. I have changed the pressure outlet to mass flow outlet boundary by giving a target mass flow rate through text mode. I am not getting the desired mass flow rate(0.045 kg/s) though all the residuals have come down to 10e-3 and there is no mass imbalance(0.36 kg/s at the inlet and exit). I have tried both target mass flow boundary available in Ver 6.1.18 and scheme file for implementing mass flow outlet. But, in both the cases it's not converged to the desired mass flow rate (0.045 kg/s).

Can anybody please help me in setting up the mass flow outlet boundary? Please help me in setting up the parameters to make the iteration for target mass flow rate algorithm faster?

Thanking you in advance.

Regards Nitin

Re: Target Mass Flow Rate
 

Just a query....

Does the flow go sonic through any part of the flowfield?

nandu

Re: Target Mass Flow Rate
 

Yes it goes above sonic at some location. But it's neither at the inlet (Total Pres BC) nor at the exit where i am defining the target mass flow rate.

Thanks for your help in advance.

Nitin

Re: Target Mass Flow Rate
 

Sounds like you have a shoked flow, that would fix the mass-flow.

Re: Target Mass Flow Rate
 

Thanks Jonas. Do you think that there would be convergence problem (getting the desired mass flow rate) of the target mass flow rate algorithm due to reverse flow at the exit? I can remember that somebody pointed out the convergence is very slow but it works.

Therefore, i would be happy if anybody gives some guideline on setting up the parameters of mass flow algorithm.

Regards Nitin

Re: Target Mass Flow Rate
 

Thanks Jonas. Do you think that there would be convergence problem (getting the desired mass flow rate) of the target mass flow rate algorithm due to reverse flow at the exit? I can remember that somebody pointed out the convergence is very slow but it works.

Therefore, i would be happy if anybody gives some guideline on setting up the parameters of mass flow algorithm.

Regards Nitin

Re: Target Mass Flow Rate
 

If you have a choked sonic throat inside your domain then the target-mass-flow outlet BC will not work - it will just continue to reduce the outlet pressure more and more but it will be impossible to reach the target mass-flow. The choked sonic throat puts a physical limit on the mass-flow which you have to accept. You can't change the physics by using a different boundary condition.