Multiple inlet and outlets

spggodd · February 27, 2016, 10:29

Hey guys,

I'm trying to simulate a capsule (hyperloop!) in a tube for my masters thesis, with a compressor on the front of the capsule and nozzle at the rear, see below.

The compressor should take 60% of the total mass flow and bypass this through the capsule to the nozzle allowing the high speed flow around the capsule to stay below Mach 1.

However I'm having a issue with setting up the compressor boundary conditions, I am currently using a pressure_outlet with a target mass flow but get reverse flow during convergence and the simulation only tends to converge to 10^-3 before repeating. The velocity at the compressor is very small (almost the same as freestream velocity) compared to the nozzle outlet, these boundarys should have the same mass flow.

Any ideas of the best way to simulate this or tell Fluent that the mass flows should be equal?

Current results

LuckyTran · February 27, 2016, 15:33

I can't see anything wrong with what you are doing.

You specified a mass-flow rate at the outlet and inlet, why are the mass-flows not the same?

Even if they were not the same, Fluent would still give you a solution because it doesn't really care where the mass-flow out went and where the mass-flow in is coming from.

The velocity at the compressor inlet should be comparable to the free-stream velocity. And based on your geometry, the velocity at the compressor outlet should be fast because of the smaller area that the same mass-flow has to squeeze through. The only thing I would suggest is to check to make sure that the pressure & density in this high velocity region is reasonably high.

spggodd · February 27, 2016, 16:12

I haven't been able to use the density according to the ideal gas law (to simulate compressible flow) as the solver blows up, I'm not really sure what to do.

February 27, 2016, 10:29	Multiple inlet and outlets	#1
spggodd Member Steven Goddard Join Date: Mar 2015 Posts: 34 Rep Power: 11	Hey guys, I'm trying to simulate a capsule (hyperloop!) in a tube for my masters thesis, with a compressor on the front of the capsule and nozzle at the rear, see below. The compressor should take 60% of the total mass flow and bypass this through the capsule to the nozzle allowing the high speed flow around the capsule to stay below Mach 1. However I'm having a issue with setting up the compressor boundary conditions, I am currently using a pressure_outlet with a target mass flow but get reverse flow during convergence and the simulation only tends to converge to 10^-3 before repeating. The velocity at the compressor is very small (almost the same as freestream velocity) compared to the nozzle outlet, these boundarys should have the same mass flow. Any ideas of the best way to simulate this or tell Fluent that the mass flows should be equal? Current results

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February 27, 2016, 15:33		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	I can't see anything wrong with what you are doing. You specified a mass-flow rate at the outlet and inlet, why are the mass-flows not the same? Even if they were not the same, Fluent would still give you a solution because it doesn't really care where the mass-flow out went and where the mass-flow in is coming from. The velocity at the compressor inlet should be comparable to the free-stream velocity. And based on your geometry, the velocity at the compressor outlet should be fast because of the smaller area that the same mass-flow has to squeeze through. The only thing I would suggest is to check to make sure that the pressure & density in this high velocity region is reasonably high.

February 27, 2016, 16:12		#3
spggodd Member Steven Goddard Join Date: Mar 2015 Posts: 34 Rep Power: 11	I haven't been able to use the density according to the ideal gas law (to simulate compressible flow) as the solver blows up, I'm not really sure what to do.