2 Questions about Density Based Solver

rap7or · August 2, 2018, 13:13

Hey guys,

I am simulating a supersonic flow (combustion with laval nozzle). As inlet I choose a massflow-inlet, which is used by 1) the Gaseous Oxygen and 2) a DPM Surface Injection of the liquid Kerosene droplets.

Question 1: When i choose the density based solver, and look at the reference values at the inlet, it shows me an Inlet Temperature of 160 K, but my Inlet Boundary condition of the Mass-Flow Inlet I typed in is 300 K. If I choose the pressure-based solver the reference-value of this inlet changes to 298 K and is realistic. My Inlet Conditions are:

Mass-Flow rate: 0.02 kg/s
Supersonic/ Inital Gauge pressure: 1e6 Pa
Oxygen Fraction: 100% (1)
Gas model: Ideal Gas

Question 2: If I choose the pressure based solver, everything works very well. Droplet evaporation, Eddy-dissipation combustion, resulting chamber pressure, etc. But as soon as the flow gets supersonic, it gets a little bit off in terms of the mach diamonds and the flow behaviour of the exhaust plume as seen in the real process. The Mach number is around 3 at maximum. Do you recommend any specific settings for this supersonic compressible flow for the pressure-based solver? Or can you give me suggestions to get the density-based solver running for this case, because the above problem (Question 1) forces me to choose the pressure-based solver.

Best regards,

Max

This picture shows the pressure-based solver results regarding the temperature. In reality it has like 7-9 mach diamonds, in this case just 2-3. I read that other studies use the density based solver, but because of Question 1 I am not able to run it with this one.

Rajaero · August 3, 2018, 00:58

Hi,
your work is amazing. can you explain how did you see the reference temperature value at inlet. did you check reference value in CFD post or fluent solver?

Thanks...

rap7or · August 3, 2018, 03:23

Quote:

Originally Posted by Rajaero

Hi,
your work is amazing. can you explain how did you see the reference temperature value at inlet. did you check reference value in CFD post or fluent solver?

Thanks...

Yes, I checked it both at „Reference Values“ and in the Standard Initialization (Fluent).

Rajaero · August 3, 2018, 03:40

Hi,
i am sure you might have checked all the possible way. I think it is better to ask ANSYS or your vendor for this issue. Because it is very strange. I never face this kind of problem.

Thanks..

August 2, 2018, 13:13	2 Questions about Density Based Solver	#1
rap7or New Member Join Date: Mar 2018 Location: Germany Posts: 16 Rep Power: 8	Hey guys, I am simulating a supersonic flow (combustion with laval nozzle). As inlet I choose a massflow-inlet, which is used by 1) the Gaseous Oxygen and 2) a DPM Surface Injection of the liquid Kerosene droplets. Question 1: When i choose the density based solver, and look at the reference values at the inlet, it shows me an Inlet Temperature of 160 K, but my Inlet Boundary condition of the Mass-Flow Inlet I typed in is 300 K. If I choose the pressure-based solver the reference-value of this inlet changes to 298 K and is realistic. My Inlet Conditions are: Mass-Flow rate: 0.02 kg/s Supersonic/ Inital Gauge pressure: 1e6 Pa Oxygen Fraction: 100% (1) Gas model: Ideal Gas Question 2: If I choose the pressure based solver, everything works very well. Droplet evaporation, Eddy-dissipation combustion, resulting chamber pressure, etc. But as soon as the flow gets supersonic, it gets a little bit off in terms of the mach diamonds and the flow behaviour of the exhaust plume as seen in the real process. The Mach number is around 3 at maximum. Do you recommend any specific settings for this supersonic compressible flow for the pressure-based solver? Or can you give me suggestions to get the density-based solver running for this case, because the above problem (Question 1) forces me to choose the pressure-based solver. Best regards, Max This picture shows the pressure-based solver results regarding the temperature. In reality it has like 7-9 mach diamonds, in this case just 2-3. I read that other studies use the density based solver, but because of Question 1 I am not able to run it with this one. Last edited by rap7or; August 2, 2018 at 15:12.

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August 3, 2018, 00:58		#2
Rajaero Member Taiwan,new north city Join Date: Aug 2017 Location: Taiwan Posts: 74 Rep Power: 9	Hi, your work is amazing. can you explain how did you see the reference temperature value at inlet. did you check reference value in CFD post or fluent solver? Thanks...

August 3, 2018, 03:40		#4
Rajaero Member Taiwan,new north city Join Date: Aug 2017 Location: Taiwan Posts: 74 Rep Power: 9	Hi, i am sure you might have checked all the possible way. I think it is better to ask ANSYS or your vendor for this issue. Because it is very strange. I never face this kind of problem. Thanks..