SimScale CAE Forum

Supersonic flow on a rocket

Hello, everyone!

I am trying to run a simulation of a rocket flying at Mach 2 with approximately 8000 Pa of atmospheric pressure por a school project.
I keep getting problems when I start the simulation run, as you can see in the solver log down below. I searched the forum for similar cases and all I could find was that the mesh was having too many illegal faces. I don´t think that is my case here, but I could try to refine it just to be sure.

The project link is https://www.simscale.com/workbench/?pid=4242617502015661596&mi=spec%3A26b3d619-61a4-49a7-bf2f-6f65ab375a71%2Cservice%3AMESHING%2Cstrategy%3A3&sh=1

Thanks a lot in advance!!
Pablo.

Hi Pablo - nice project you have there!

Would be nice if we can make this work, have the Falcon Heavy in my Workspace which also needs to be finished at some point :smiley: I saw that you have used a density based formulation which sometimes struggles for strong shocks. I remember that my colleagues @Get_Barried & @1318980 worked on compressible simulations in the past who might add their two cents here. Setup wise the simulation looks quite good but I would consider optimizing the mesh (not only have a bigger distance in front of the rocket from the inlet but only work with less refinements which sometimes helps) - however you can see that the layers are not uniformly distributed along the rocket…

All the best!

Jousef

Hi jousefm!

Thanks a lot for the answer. I will take into consideration the suggestions you made, but do you really think it is necessary to have a bigger distance in front of the rocket from the inlet? I made this small distance on purpose because the air in front of the rocket does not “know” that the rocket is coming because it is going supersonic.

Cheers!
Pablo

Hey Pablo!

Indeed you can try it with the small distance and see if that works - I usually give it a bit more space. Let us know how your progress goes and if you need any assistance.

Best,

Jousef

Hi @puboldi,

We’ve had some difficulty getting supersonic flow to behave properly. I suggest trying out a run and we’ll work out solutions from there.

And yes that is mostly true that the inlet distance can be small provided you are using a laminar model.

Cheers.

Regards,
Barry

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Hi, guys!

I re-meshed the model giving it a little bit more space in front of the rocket and making it a little simpler, then I made another run (run 8).

The problem now was that the instance storage run out of space. The suggestion says that I reduce the number of timesteps that are stored by increasing the write interval in the simulation control settings. This is very strange, because I specifically set the write interval big enough so that it writes only 7 times.

I made this calculation:
start time: 0 s
end time: 0.35 s
delta t: 0.005 s

So, there should be 0.35/0.005 = 70 steps. I set the write interval to 10 timesteps, so it should only write 7 times, but the simulation returned the error anyway.

I will make another run setting the “Write control” parameter to “Adjustable runtime” and setting the “Write interval” value to “0.175 s” so that it only writes the result twice.

I hope I’m doing this right.

Cheers!
Pablo

Hi @puboldi,

I suggest deleting all of your runs that you do not require and other projects/geometries that you also may not require to free up the storage space allocated to you.

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Oh! I didn’t know I had limited storage space. Thanks for the tip, I deleted what I didn’t need.

I think I know what was wrong with my setup.
Reading the solver log and investigating here https://www.simscale.com/blog/2017/08/cfl-condition/ I could figure out that my simulation crashes because it reaches a Courant number higher than 1 and I think this is a combination of a thin mesh, a fast speed flow and a big “delta t”. I will have to find a balance between this 3 variables in order to find a good result because a thinner mesh will necesarily require a smaller “delta t” and that will result in a longer simulation run.

Whatever progress I make, I will update it here in case someone has the same problems I had.

Thanks a lot!

Cheers!
Pablo

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