[blastFoam] Hypersonic Wind Tunnel Nonphysical Results

noidea · February 10, 2021, 07:05

Hello everyone,

I am a student working on my master thesis right now doing a simulation of a hypersonic wind tunnel with blastFoam 4.0. The setup can be seen in the sketch attached to this post. The initialization is done by setting up two states, one high pressure, high temperature state in the first chamber (leftmost), and a second, low pressure, low temperature state in the rest of the domain. I'm using air as my fluid medium . For comparison, I have experimental data provided to me by my tutors.

But by doing all this, I have encountered a couple of problems, namely:
- nonphysical temperature spikes in the shock wave (to a range of +10E5 K)
- while the qualitative flow phenomena seam good and the values for velocity, Mach number and pressure are in an range we expected, the time in which they occur is off (for example, the shock wave hits a specific point in this domain about 10 times earlier than expected from experimental results).

These problems occur for a 2D case as well as a wedge or a full 3D case.

I'm not sure where my problem is right now, so every hint would help a lot.

Best regards
Daniel

Sketch_hy_1.jpg Sketch_hy_2.jpg Sketch_hy_3.jpg

jheylmun · March 9, 2021, 10:57

Hi Daniel,
Could you provide some more information on your case setup? For example the numerical schemes (flux scheme, time integrator, and reconstruction method), thermodynamic models used, and boundary conditions.

One last question, what is the gas used in the experimental setup?

Thanks,
Jeff

noidea · March 18, 2021, 08:41

Hi Jeff,

sorry for my late answer.
We already found the solution for this problem. It was about the fact that we calculated it 2D, the numerical and experimental results were in good agreement after running it 3D for pressure and temperature.

But to clarify:

- Flux scheme, Time integration and reconstuction method can be seen in the attached fvScheme and fvSolution files

- Gas & Thermodynamical model: Air, ideal gas law (air has also been used in the experimental setup)
- Turbulence: laminar

- boundary conditions: all are wall BC (zeroGradient in T, p, rho, noSlip in U) (besides the "sides", which are empty BC).

Best regards,
Daniel

fvSchemes.txt

fvSolution.txt

February 10, 2021, 07:05	Hypersonic Wind Tunnel Nonphysical Results	#1
noidea New Member Daniel Join Date: Oct 2020 Posts: 2 Rep Power: 0	Hello everyone, I am a student working on my master thesis right now doing a simulation of a hypersonic wind tunnel with blastFoam 4.0. The setup can be seen in the sketch attached to this post. The initialization is done by setting up two states, one high pressure, high temperature state in the first chamber (leftmost), and a second, low pressure, low temperature state in the rest of the domain. I'm using air as my fluid medium . For comparison, I have experimental data provided to me by my tutors. But by doing all this, I have encountered a couple of problems, namely: - nonphysical temperature spikes in the shock wave (to a range of +10E5 K) - while the qualitative flow phenomena seam good and the values for velocity, Mach number and pressure are in an range we expected, the time in which they occur is off (for example, the shock wave hits a specific point in this domain about 10 times earlier than expected from experimental results). These problems occur for a 2D case as well as a wedge or a full 3D case. I'm not sure where my problem is right now, so every hint would help a lot. Best regards Daniel Sketch_hy_1.jpg Sketch_hy_2.jpg Sketch_hy_3.jpg

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March 9, 2021, 10:57		#2
jheylmun New Member Jeff Heylmun Join Date: Mar 2016 Location: Ames, IA Posts: 1 Rep Power: 0	Hi Daniel, Could you provide some more information on your case setup? For example the numerical schemes (flux scheme, time integrator, and reconstruction method), thermodynamic models used, and boundary conditions. One last question, what is the gas used in the experimental setup? Thanks, Jeff

March 18, 2021, 08:41		#3
noidea New Member Daniel Join Date: Oct 2020 Posts: 2 Rep Power: 0	Hi Jeff, sorry for my late answer. We already found the solution for this problem. It was about the fact that we calculated it 2D, the numerical and experimental results were in good agreement after running it 3D for pressure and temperature. But to clarify: - Flux scheme, Time integration and reconstuction method can be seen in the attached fvScheme and fvSolution files - Gas & Thermodynamical model: Air, ideal gas law (air has also been used in the experimental setup) - Turbulence: laminar - boundary conditions: all are wall BC (zeroGradient in T, p, rho, noSlip in U) (besides the "sides", which are empty BC). Best regards, Daniel fvSchemes.txt fvSolution.txt