SimScale CAE Forum

Nozzle Compressible Flow

Hello to everyone!

I am working in a compressible flow through a nozzle and I am having a lot of issues. First, I had the problem explained in this Topic but after ramping the pressure I started having results. The problem is that the results are not physically possible (negative pressure, high velocities, etc). All of this was a Steady-State simulation.

Then, I read in a forum that rhoSimpleFoam does not deal well with shock waves, etc. So I created a Transient simulation and, now, I do not have negative pressure values, but the results are not good (the flow behaves as subsonic when it should be supersonic, at least analyticaly). So I thought that trying to improve the residuals (that didn’t look very good) would help. I started messing with the numerics as I have readed in different Topics, but nothing.

If someone have any idea, please, that would be awesome.

Here is my project:
https://www.simscale.com/projects/Sguares/nozzle_compressible_flow_3/

Here there are two simulations (steady-state and tranient), and a lot of Runs changing BC’s, numerics, etc. Sorry about the mess.

Thank you!

Santi
Pd: the mesh looks fine i think.

Hi Santi!

Tagging @Get_Barried here who also worked on some compressible sims in the past. I might have a look at the setup at a later point. @CFD-SQUAD, feel free to add your two cents here.

Best,

Jousef

1 Like

Hi @Sguares,

What is the mach number you are looking at? I assume that you are trying to replicate shock waves internally. This may be an issue. While it is true that rhoSimpleFoam does not deal well with shocks at all, neither does rhoPimpleFoam.

Back when I used to handle shock simulations, the only viable solver that is able to replicate shocks was the rhoCentralFoam. That solver is however disabled now on Simscale. Have you looked through whether rhoPimpleFoam is able to handle shocks yet? I have been out of the loop for awhile, maybe someone has found a workaround.

Do let me know.

Cheers.

Regards,
Barry

1 Like

Hi @Get_Barried ,

Thanks for your anwser,
I do not want to replicate shock waves, I am trying to have Ma=1.7 at the exit of the nozzle. I have tried reducing the pressure to avoid the shock waves but I have the same result. I do not have a supersonic flow…

Lately I have been working on this and my conclusion is that rhoPimpleFoam does not handle shock waves (and transonic flow).
Thanks,

Santi

Hi @Sguares,

Well usually above Mach 1.3 is considered to be supersonic flow.

Nevertheless, rhoPimpleFoam is not able to handle shock waves. High sub-sonic flow and low transonic flow like between Mach 0.7 to Mach 1.1 should be possible but I myself haven’t tried to replicate data to evaluate the performance of transonic flow itself.

If you do need to replicate flow above Mach 1.3, suggest to switch to a local Openfoam run using rhoCentralFoam. That might give you the results you need but keep in mind the computational requirements. Steady-state analysis is not possible as far as I know.

Cheers.

Regards,
Barry