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Old   December 11, 2019, 12:50
Default Divergence in Nozzle
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I am trying to simulate an axisymmetric C-D nozzle at Mach 6 in SU2, but the solution keeps diverging after a few thousand iterations. Any recommendations to solve this issue? I've tried changing the CFL number, changing the relaxation coefficients, and changing the JST coefficients.
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Old   December 11, 2019, 14:54
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Hi jcrownbey,


Thanks for your question. How do the residuals evolve? What are your boundary conditions?


One thing that may help, would be to use the AUSM convective flux, as it is more suited for high speed flows. Disabling multigrid could help as well.


Let me know if this helps. Also, feel free to attach your config file so we can take a better look


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Old   December 11, 2019, 15:14
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Wally,

Thank you for your response.

In a simulation I have done in a 2-D nozzle at Mach 2, I compared AUSM, ROE (2nd order), and JST. AUSM had too many oscillations in the solution.

Here is a piece of my config file for the BC's:

% -------------------- BOUNDARY CONDITION DEFINITION --------------------------%
% Euler wall boundary marker(s) (NONE = no marker)
MARKER_EULER= ( Wall )

% Navier-Stokes (no-slip), constant heat flux wall marker(s) (NONE = no marker)
% Format: ( marker name, constant heat flux (J/m^2), ... )
%MARKER_HEATFLUX= ( UPPER_WALL, 0.0, LOWER_WALL, 0.0 )
% Riemann boundary marker(s) (NONE = no marker)
% Format: (marker, data kind flag, list of data)
MARKER_RIEMANN= ( Inflow, TOTAL_CONDITIONS_PT,3618647, 1904.4, 1.0, 0.0, 0.0, Outflow, STATIC_PRESSURE, 2021.804, 0.0, 0.0, 0.0, 0.0)

MARKER_SYM= ( Symmetry ) % Symmetry boundary marker(s) (NONE = no marker)

Also, attached is a picture of the boundaries of my nozzle.

The left line is my Inflow, the top contour is a inviscid wall (inviscid solution), and the bottom line is my Symmetry. The box on the right of the nozzle is to simulate the nozzle after it exits to the atmosphere. The left line, top line, and right line of the box are set to Outflow.

I do not have mutigrid active for my simulation.
Attached Images
File Type: png m6.png (3.2 KB, 28 views)
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Old   December 11, 2019, 15:24
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Hmmm interesting. Your boundary conditions look good. Did ROE look good/converge? Are you running with version 7.0?

You could try running explicitly with a small CFL number (if you havent tried).

JST should be able to converge this so Im a bit stumped at the moment.
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Old   December 11, 2019, 15:29
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In the Mach-2 nozzle, ROE converged, but the solution was not as clean as JST. I have tried running with CFL_ADAPT on, but it still diverges. For the Mach-2 nozzle, I had to run with a CFL no. of 10 to get a converged solution.

I am running with version 6.2
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Old   December 12, 2019, 02:16
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Did you add to your config file to represent axisymmetry?



% Dimension of problem (YES, NO)
AXISYMMETRIC = YES
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Old   December 12, 2019, 10:47
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I did have the axisymmetric option on
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Old   December 12, 2019, 14:22
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The simulation works fine for a thousand iterations or so. The solution then diverges, usually having non-physical points after a while.
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Old   December 13, 2019, 03:21
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Its hard to give some support for older versions. Think about using the v7 and try your case again.
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Old   December 13, 2019, 06:55
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After looking at the additions to the new version, the only way I would be affected is the variables names would be changed.
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