Mass flow inlet BC for air with different densities

John3945 · February 10, 2022, 06:38

I am trying to simulate the cold flow in a swirl stabilized burner (shown in figure). It has a main inlet which supplies 25g/s of air at 1 bar and a secondary inlet in the burner which inputs 0.875g/s of air at 5 bar. How do I implement this in Fluent?
I tried using the density based solver which gives me the option to add the gauge pressure in the mass-flow-inlet BC but my PC just froze on trying to run the simulation (I have around 10 million cells in my mesh, I guess this is the cause for that. However, I cannot reduce this). Is there any way I could run this case using the pressure based solver? Thank you!

mesh_3D.jpg

mesh_cuttingplane.jpg

LuckyTran · February 10, 2022, 09:30

You can't really specify both mass flow rate and pressure at the inlet unless it is supersonic.

What you should do though is use a mass flow inlet and specify the mass flow rate and the total temperature. The pressure should be close to what you want. If you want to pressure to be exactly the same then you need to iterate on one or more if your settings, including the outlet BC.

You can use the pressure based solver if you want.

John3945 · February 13, 2022, 07:46

Quote:

Originally Posted by LuckyTran

You can't really specify both mass flow rate and pressure at the inlet unless it is supersonic.

What you should do though is use a mass flow inlet and specify the mass flow rate and the total temperature. The pressure should be close to what you want. If you want to pressure to be exactly the same then you need to iterate on one or more if your settings, including the outlet BC.

You can use the pressure based solver if you want.

Thanks for your reply LuckyTran. I tried what you suggested but the solver calculated a different value of static temperature at my second inlet than reality. Both the inlets are supposed to input fluids at static temperature of 573K. The static pressure was also way lesser than what I wanted, only around 1.06 bar.
Capture.PNG
Do you know why this may be and how I could rectify it? Thanks.

LuckyTran · February 13, 2022, 20:50

Because you physically can't impose a static pressure and temperature at an inlet unless it is supersonic. Adjust your total pressure and temperature until the static ones match what you want. This is computational fluid dynamics, not computational thermostatics. We don't impose static properties at inlets in fluid dynamics.

February 10, 2022, 06:38	Mass flow inlet BC for air with different densities	#1
John3945 New Member John Paul Join Date: Feb 2022 Posts: 2 Rep Power: 0	I am trying to simulate the cold flow in a swirl stabilized burner (shown in figure). It has a main inlet which supplies 25g/s of air at 1 bar and a secondary inlet in the burner which inputs 0.875g/s of air at 5 bar. How do I implement this in Fluent? I tried using the density based solver which gives me the option to add the gauge pressure in the mass-flow-inlet BC but my PC just froze on trying to run the simulation (I have around 10 million cells in my mesh, I guess this is the cause for that. However, I cannot reduce this). Is there any way I could run this case using the pressure based solver? Thank you! mesh_3D.jpg mesh_cuttingplane.jpg

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Calculate Mass Flowrate and Mass Flow Averaged Total Pressure at inlet and outlet	coolcrasher	OpenFOAM Post-Processing	7	November 4, 2021 05:57
mass flow inlet and pressure outlet with target mass flow rate	Zigainer	FLUENT	13	October 26, 2018 06:58
Access inlet mass flow value (target mass flow rate)	YCarv	Fluent UDF and Scheme Programming	2	April 1, 2018 09:09
Low Mixing time Problem	Mavier	CFX	5	April 29, 2013 01:00
Mass Flow Inlet	Pravir Kumar Rai	FLUENT	0	February 19, 2003 15:03

February 10, 2022, 09:30		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,751 Rep Power: 66	You can't really specify both mass flow rate and pressure at the inlet unless it is supersonic. What you should do though is use a mass flow inlet and specify the mass flow rate and the total temperature. The pressure should be close to what you want. If you want to pressure to be exactly the same then you need to iterate on one or more if your settings, including the outlet BC. You can use the pressure based solver if you want.

February 13, 2022, 20:50		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,751 Rep Power: 66	Because you physically can't impose a static pressure and temperature at an inlet unless it is supersonic. Adjust your total pressure and temperature until the static ones match what you want. This is computational fluid dynamics, not computational thermostatics. We don't impose static properties at inlets in fluid dynamics.