outlet boundary

protocol · July 25, 2015, 06:38

i have an subsonic flow in the outlet i want to find the value of pressure at the exit in star ccm manual its given that for subsonic flow pressure at outlet must be specified is it ok to target mass flow option and give inlet mass flow at outlet will this help me in finding out the pressure at exit boundary

fluid23 · July 28, 2015, 11:27

that is what I would do.

the mass flow inlet varies its pressure/velocity distribution to acheive the required flow rate. you will probably want a mass flow averaged report of pressure on the inlet. Do not create a report for mass flow at the inlet, however. It will pretty much always read what you input. Instead create a derived part a few diameters upstream and measure mass flow there. It will be give a better indication of performance.

also, I will mention... don't put 2 mass flow inlets. one pulling the flow downstream is enough. your upstream boundary should be a stagnation inlet or something like that.

ggulgulia · July 29, 2015, 11:39

Hi

I don't think making the outlet boundary as inlet will give you a correct value of pressure. Even if you switch the inlet and outlet boundaries, the pressure values will not represent what one may get in testing with original boundary condition (which is very obvious)

As far as my experience is concerned, CCM+ gives fairly good result of pressure values at interfaces and boundaries. you can create extrusion layers of mesh (say 100 mm , 50 layers) if the expansion to atmosphere (0.0 static pressure) is resulting in erroneous values. This is what we usually do for our simulations.

July 25, 2015, 06:38	outlet boundary	#1
protocol New Member Join Date: Feb 2015 Posts: 26 Rep Power: 11	i have an subsonic flow in the outlet i want to find the value of pressure at the exit in star ccm manual its given that for subsonic flow pressure at outlet must be specified is it ok to target mass flow option and give inlet mass flow at outlet will this help me in finding out the pressure at exit boundary

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July 28, 2015, 11:27		#2
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	that is what I would do. the mass flow inlet varies its pressure/velocity distribution to acheive the required flow rate. you will probably want a mass flow averaged report of pressure on the inlet. Do not create a report for mass flow at the inlet, however. It will pretty much always read what you input. Instead create a derived part a few diameters upstream and measure mass flow there. It will be give a better indication of performance. also, I will mention... don't put 2 mass flow inlets. one pulling the flow downstream is enough. your upstream boundary should be a stagnation inlet or something like that.

July 29, 2015, 11:39		#3
ggulgulia Senior Member Gajendra Gulgulia Join Date: Apr 2013 Location: Munich Posts: 144 Rep Power: 13	Hi I don't think making the outlet boundary as inlet will give you a correct value of pressure. Even if you switch the inlet and outlet boundaries, the pressure values will not represent what one may get in testing with original boundary condition (which is very obvious) As far as my experience is concerned, CCM+ gives fairly good result of pressure values at interfaces and boundaries. you can create extrusion layers of mesh (say 100 mm , 50 layers) if the expansion to atmosphere (0.0 static pressure) is resulting in erroneous values. This is what we usually do for our simulations.