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High Mach Number Flow, weird things for inlet settings when imposing the total/static conditions

Posted Aug 1, 2014, 11:50 a.m. EDT Computational Fluid Dynamics (CFD) Version 5.2 1 Reply

Daniel Guariglia
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Greetings,

As the title state, something weird is happening I think. I am simulating a coaxial jet, 2D axyalsymmetric, surrounded by slow moving air (M = 0.01), with the external flow being chocked.
I imposed the following TOTAL inlet condition in the external flow, characteristics based:

p0 = 246465
T = 293.15
M = 0.1 (don't know why it should be needed...)

After many simulations converged (unfortunately), I realized there was something wrong checking the mass flow through the chocked nozzle, significantly different from the theoretical one (and by the way, I found also the mass flow slightly decreasing from the inlet to the throat O.o!).
Then I checked the pressure in the results, at the inlet, and I found those values:

p=p0= 284000
T = 303
M = 0.01

Completely wrong! Now, for trying, I put the same values, with STATIC, and all was exactly the same.
Then I tried both STATIC and TOTAL with M = 0.01, and the pressure at the inlet was correct.

Useless to say, I checked and re-checked everything. Gamma was ok, 1.4.
Something strange is happening here... Any clues?

Thank you
1 Reply Last Post Jul 17, 2016, 9:12 p.m. EDT
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Hello Daniel Guariglia

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peiran yin
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Posted: 8 years ago Jul 17, 2016, 9:12 p.m. EDT
Hi,I'm doing some similar works like yours with the high mach number flow model.
It's a 2-D time dependent question with compressible air.
I have set the inlet condition as :
Pin_tot= 0.15[atm], Tin_tot=330K, M=0.8
However, after some time(2us),the results show that, at the inlet all these condistions have changed.
Don't these conditions keeps invariant in the process?


If you have an answer to this now,hope for your apply.
Hi,I'm doing some similar works like yours with the high mach number flow model. It's a 2-D time dependent question with compressible air. I have set the inlet condition as : Pin_tot= 0.15[atm], Tin_tot=330K, M=0.8 However, after some time(2us),the results show that, at the inlet all these condistions have changed. Don't these conditions keeps invariant in the process? If you have an answer to this now,hope for your apply.

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