What settings do I do for the outlet if I only know the inlet conditions?

Ryan T · September 22, 2021, 19:17

What settings do I do for a density based solver if I only know the inlet conditions? I'm trying to do a validation study for a paper but I don't know how the authors did the outlet conditions. They only mention the boundary conditions for the air and hydrogen inlets.

LuckyTran · September 23, 2021, 00:58

Does it even matter? I see that both inlets have a Mach number of 1 and 2, so downstream BC's shouldn't really affect the problem as long as you set a reasonable outlet pressure that maintains the sonic conditions at the inlets.

Otherwise the inlets are overconstrained. Something has to be relaxed.

If you really care about matching all the numbers at the inlet then one of the constraints needs to become a soft constraint. That is, you iterate something else until that constraint is satisfied. For example, you could use a pressure outlet BC and then iterate the outlet pressure until the inlet pressure matches the table.

Ryan T · September 23, 2021, 23:58

Quote:

Originally Posted by LuckyTran

Does it even matter? I see that both inlets have a Mach number of 1 and 2, so downstream BC's shouldn't really affect the problem as long as you set a reasonable outlet pressure that maintains the sonic conditions at the inlets.

Otherwise the inlets are overconstrained. Something has to be relaxed.

If you really care about matching all the numbers at the inlet then one of the constraints needs to become a soft constraint. That is, you iterate something else until that constraint is satisfied. For example, you could use a pressure outlet BC and then iterate the outlet pressure until the inlet pressure matches the table.

Thanks for the info, I'll try that then.

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September 23, 2021, 00:58		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,668 Rep Power: 65	Does it even matter? I see that both inlets have a Mach number of 1 and 2, so downstream BC's shouldn't really affect the problem as long as you set a reasonable outlet pressure that maintains the sonic conditions at the inlets. Otherwise the inlets are overconstrained. Something has to be relaxed. If you really care about matching all the numbers at the inlet then one of the constraints needs to become a soft constraint. That is, you iterate something else until that constraint is satisfied. For example, you could use a pressure outlet BC and then iterate the outlet pressure until the inlet pressure matches the table.