Mass flow outlet BC

Prabin Pradhananga_22497

Hi experts,

I was wondering if acuSolve has mass flow outlet boundary condition. I checked the documentation but could not find one. Can anyone confirm that?

Thanks.

acupro

What is the reason for specifying a mass flow at the outlet?

Generally we don't like to do that, as the methods we have for mass flow directly will also 'generate' a profile at the boundary, which will typically not be the same as the flow profile approaching that boundary, forcing the flow to adjust to that specified profile.

Some people use a typical Inflow Simple BC with a negative value for the mass flow.  Others use a typical outflow, but than add a Surface Integrated Condition (through advanced boundaries) to specify the mass flow.  (For this second option, I suggest waiting for the 2022.1 release of HyperWorks CFD, as currently there's an issue where the main BC is removed from a surface with an Advanced BC.)

If it's a single inlet and single outlet, it's usually more robust and more physical to specify the mass flow at the inlet and use the standard outflow.  If there are multiple outlets and you know the flow split, you can use the methods above, or use the pressure loss factor (trial and error, may take a few runs) on one of the outlets to adjust the flow rate.

Feroz

Hallo, I'm not one of the experts, but in this situation I would specify the stagnation pressure as a BC. Hope this helps in the mean time until one of the others reply.

acupro

What is the reason for specifying a mass flow at the outlet?

Generally we don't like to do that, as the methods we have for mass flow directly will also 'generate' a profile at the boundary, which will typically not be the same as the flow profile approaching that boundary, forcing the flow to adjust to that specified profile.

Some people use a typical Inflow Simple BC with a negative value for the mass flow.  Others use a typical outflow, but than add a Surface Integrated Condition (through advanced boundaries) to specify the mass flow.  (For this second option, I suggest waiting for the 2022.1 release of HyperWorks CFD, as currently there's an issue where the main BC is removed from a surface with an Advanced BC.)

If it's a single inlet and single outlet, it's usually more robust and more physical to specify the mass flow at the inlet and use the standard outflow.  If there are multiple outlets and you know the flow split, you can use the methods above, or use the pressure loss factor (trial and error, may take a few runs) on one of the outlets to adjust the flow rate.