Supersonic (Compressible) Inlet Boundary Conditions

Supersonic · February 12, 2016, 17:42

Hi, can anyone help me? I am trying to model a supersonic inlet to a wind tunnel. According to the user's guide, I am supposed to use a pressure-inlet boundary condition. I am trying to model total pressure of 1.2 MPa, static pressure 82 kPa, total temp 1980 K, and Mach 2.5. When I use the pressure-inlet, there is no where to specify Mach number. When I run the simulation without it, the inlet appears to be closer to 0.5 Mach. What am I doing wrong? Thank you!

LuckyTran · February 13, 2016, 13:43

You do not specify Mach number explicitly but by specifying the total and static pressure. You probably didn't specify the static pressure.

Specify the stagnation pressure / total pressure as 1.2 MPa.
Specify the stagnation / total temperature as 1980 K.
Specify the supersonic / initial pressure as 82 kPa.

Just remember that all pressures are gauge pressures. So set your operating pressure and pressure inputs accordingly.

Supersonic · February 13, 2016, 18:25

Hi LuckyTran,
Thank you for replying, unfortunately, I have done all of that. I set those as the gauge pressures and set operating pressure to 0 to make them total pressures. When I do this, in inlet Mach number is about 0.5. Can you think of anything else I may be doing wrong? Thank you for the help!
Supersonic

LuckyTran · February 13, 2016, 19:18

Make sure for your pressure inlet you have specified two pressures (the total pressure and the supersonic static pressure) and total temperature.

The other thing to check are your other boundary conditions. Make sure you have the correct downstream conditions to allow a supersonic flow.

Supersonic · March 30, 2016, 13:09

Everything you said was correct. However, you also need to select "Use Specified Initial Pressure on Inlets" under "Solution Initialization" then "More Settings..." to get this to work. It took me 1.5 months to figure this out....

anuragarya · October 3, 2017, 15:41

I am having convergence problem when I am doing exactly similar type of problem. I am ending with very large mach number at upstream at some point locations (singularity are coming). I am amateur in CFD, Pls help. Thank you for providing initialisation technique.

February 12, 2016, 17:42	Supersonic (Compressible) Inlet Boundary Conditions	#1
Supersonic New Member Join Date: Feb 2016 Posts: 9 Rep Power: 10	Hi, can anyone help me? I am trying to model a supersonic inlet to a wind tunnel. According to the user's guide, I am supposed to use a pressure-inlet boundary condition. I am trying to model total pressure of 1.2 MPa, static pressure 82 kPa, total temp 1980 K, and Mach 2.5. When I use the pressure-inlet, there is no where to specify Mach number. When I run the simulation without it, the inlet appears to be closer to 0.5 Mach. What am I doing wrong? Thank you!

October 3, 2017, 15:41	Same simulation convergence problem	#6
anuragarya New Member Anurag Arya Join Date: Mar 2014 Location: Nagercoil Posts: 1 Rep Power: 0	I am having convergence problem when I am doing exactly similar type of problem. I am ending with very large mach number at upstream at some point locations (singularity are coming). I am amateur in CFD, Pls help. Thank you for providing initialisation technique.

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February 13, 2016, 13:43		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,754 Rep Power: 66	You do not specify Mach number explicitly but by specifying the total and static pressure. You probably didn't specify the static pressure. Specify the stagnation pressure / total pressure as 1.2 MPa. Specify the stagnation / total temperature as 1980 K. Specify the supersonic / initial pressure as 82 kPa. Just remember that all pressures are gauge pressures. So set your operating pressure and pressure inputs accordingly.

February 13, 2016, 18:25		#3
Supersonic New Member Join Date: Feb 2016 Posts: 9 Rep Power: 10	Hi LuckyTran, Thank you for replying, unfortunately, I have done all of that. I set those as the gauge pressures and set operating pressure to 0 to make them total pressures. When I do this, in inlet Mach number is about 0.5. Can you think of anything else I may be doing wrong? Thank you for the help! Supersonic

February 13, 2016, 19:18		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,754 Rep Power: 66	Make sure for your pressure inlet you have specified two pressures (the total pressure and the supersonic static pressure) and total temperature. The other thing to check are your other boundary conditions. Make sure you have the correct downstream conditions to allow a supersonic flow.

March 30, 2016, 13:09		#5
Supersonic New Member Join Date: Feb 2016 Posts: 9 Rep Power: 10	Everything you said was correct. However, you also need to select "Use Specified Initial Pressure on Inlets" under "Solution Initialization" then "More Settings..." to get this to work. It took me 1.5 months to figure this out....