Shock waves

hesamking · July 10, 2014, 14:42

However, when I change it to free slip adiabatic for top and bottom and use
domain initialization the same as the inlet.
I get the attached results with the residuals moving in 1e-8 to 1e10 range and goes on until the heat transfer and turbulence converges!!!!
however the heat transfer and turbulence ones seems to converge.monitor222.jpg

ccl-2-1.txt

CCL-2.txt
Thanks

hesamking · July 10, 2014, 14:43

I did that and sent you the CCL file
Thanks

Quote:

Originally Posted by singer1812

You are running a steady state analysis. Try setting your initial conditions to U=500m/s.

singer1812 · July 10, 2014, 14:46

Ok, so what is the problem?

hesamking · July 10, 2014, 14:48

Is it ok that it is over converging?
Does it mean it is already converged in terms of momentum?
SO there is nothing wrong with that?
So for transient simulation, I should just change the analysis type and keep the rest as before?

singer1812 · July 10, 2014, 14:50

Over converge? Never heard of such a thing.

Steady state is working.

Transient should work just fine. I have done many of these problems.

Typically I model a large caliber gun blast and blow down. Pressure wave travels just fine.

hesamking · July 10, 2014, 15:01

It was a made up word. sorry.
I meant what does it mean when you set your convergence criteria to 1e-6
but the momentum components are converged from the beginning of the run like this case?
It seems to be running for now, hopefully it won't fail.
Thank you again.
Best,
Hesam

hesamking · July 10, 2014, 20:37

Dear Edmund,
The flow in a channel went ok. however, back to my original problem, supersonic flow over a forward-facing step, my steady state run diverges and fails after 120 iterations. I used the same BC for this problem and just defined no-slip BC on the step surfaces. I have attached the geometry and the CCL file. I would appreciate if you could take a look. the velocity is 1041.84 at the inlet corresponding to M = 3 and the domain initialization is the same as the inlet.
thanks,
Hesam

singer1812 · July 11, 2014, 08:57

I would guess that your Boundary conditions are too close to your step. For sure, a shock wave is hitting that step, reflecting back and hitting your opening.

Move the BCs further away.

Also, turn on high speed numerics. its under solver control.

Dont use Auto Timescale. Use a Physical One, for starters you can try L_characteristic/U, or use Local Timescale first then switch to Physical.

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July 10, 2014, 14:42		#21
hesamking Member Hesam Moghaddam Join Date: Mar 2012 Posts: 49 Rep Power: 14	However, when I change it to free slip adiabatic for top and bottom and use domain initialization the same as the inlet. I get the attached results with the residuals moving in 1e-8 to 1e10 range and goes on until the heat transfer and turbulence converges!!!! however the heat transfer and turbulence ones seems to converge.monitor222.jpg ccl-2-1.txt CCL-2.txt Thanks

July 10, 2014, 14:46		#23
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 21	Ok, so what is the problem?

July 10, 2014, 14:48		#24
hesamking Member Hesam Moghaddam Join Date: Mar 2012 Posts: 49 Rep Power: 14	Is it ok that it is over converging? Does it mean it is already converged in terms of momentum? SO there is nothing wrong with that? So for transient simulation, I should just change the analysis type and keep the rest as before?

July 10, 2014, 14:50		#25
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 21	Over converge? Never heard of such a thing. Steady state is working. Transient should work just fine. I have done many of these problems. Typically I model a large caliber gun blast and blow down. Pressure wave travels just fine.

July 10, 2014, 15:01		#26
hesamking Member Hesam Moghaddam Join Date: Mar 2012 Posts: 49 Rep Power: 14	It was a made up word. sorry. I meant what does it mean when you set your convergence criteria to 1e-6 but the momentum components are converged from the beginning of the run like this case? It seems to be running for now, hopefully it won't fail. Thank you again. Best, Hesam

July 11, 2014, 08:57		#28
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 21	I would guess that your Boundary conditions are too close to your step. For sure, a shock wave is hitting that step, reflecting back and hitting your opening. Move the BCs further away. Also, turn on high speed numerics. its under solver control. Dont use Auto Timescale. Use a Physical One, for starters you can try L_characteristic/U, or use Local Timescale first then switch to Physical.