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August 27, 2020, 05:05 
Divergence issues

#1 
New Member
William Haigh
Join Date: Aug 2020
Posts: 20
Rep Power: 5 
Hi all,
I am new to SU2 and I am attempting to find a CFD solution including oblique shocks in a scramjet inlet. I created a mesh using Gmsh which I can't attach here. I have also written a configuration file. However, when I try to run it, it tells me that SU2 has diverged. If someone could take a look at my mesh and configuration files and tell me what errors there are. Again, I am very new to this so there could be many! I added a picture of the inlet scramjet for a better understanding. here is the script of my conf file: %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % % % SU2 configuration file % % Case description: Scramjet inlet (M1 = 5.1) % % Author: William Haigh % % % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %  DIRECT, ADJOINT, AND LINEARIZED PROBLEM DEFINITION % % % Physical governing equations (EULER, NAVIER_STOKES, % TNE2_EULER, TNE2_NAVIER_STOKES, % WAVE_EQUATION, HEAT_EQUATION, LINEAR_ELASTICITY, % POISSON_EQUATION) SOLVER = EULER % Specify turbulent model (NONE, SA, SA_NEG, SST) KIND_TURB_MODEL = NONE % Mathematical problem (DIRECT, ADJOINT, LINEARIZED) MATH_PROBLEM = DIRECT % Restart solution (NO, YES) RESTART_SOL = NO %  COMPRESSIBLE FARFIELD DEFINITION % % Mach number (nondimensional, based on the freestream values) MACH_NUMBER = 5.1 % Angle of attack (degrees, only for compressible flows) AoA = 0.0 % Init option to choose between Reynolds (default) or thermodynamics quantities % for initializing the solution (REYNOLDS, TD_CONDITIONS) INIT_OPTION = TD_CONDITIONS % Freestream option to choose between density and temperature (default) for % initializing the solution (TEMPERATURE_FS, DENSITY_FS) FREESTREAM_OPTION = TEMPERATURE_FS % Freestream pressure (101325.0 N/m^2, 2116.216 psf by default) FREESTREAM_PRESSURE = 4488.0 % Freestream temperature (288.15 K, 518.67 R by default) FREESTREAM_TEMPERATURE = 217.92 % Reynolds length (1 m by default) REYNOLDS_LENGTH = 1.0 %  REFERENCE VALUE DEFINITION % % % Reference origin for moment computation REF_ORIGIN_MOMENT_X = 0.25 REF_ORIGIN_MOMENT_Y = 0.00 REF_ORIGIN_MOMENT_Z = 0.00 % % Reference length for pitching, rolling, and yawing nondimensional moment REF_LENGTH= 1.0 % % Reference area for force coefficients (0 implies automatic calculation) REF_AREA= 1.0 %  IDEAL GAS PROPERTIES % % Different gas model (STANDARD_AIR, IDEAL_GAS, VW_GAS, PR_GAS) FLUID_MODEL = IDEAL_GAS % Ratio of specific heats (1.4 default and the value is hardcoded for the model STANDARD_AIR) GAMMA_VALUE = 1.4 % Specific gas constant (287.058 J/kg*K default, hardcoded for model STANDARD_AIR) GAS_CONSTANT = 287 %  BOUNDARY CONDITION DEFINITION % % Euler wall boundary marker(s) (NONE = no marker) MARKER_EULER = ( Wall ) % Supersonic inlet boundary marker(s) (NONE = no marker) % Format: (inlet marker, temperature, static pressure, velocity_x, % velocity_y, velocity_z, ...) i.e. primitive variables specified MARKER_SUPERSONIC_INLET = ( Inlet, 217.92, 4488, 1509.119697, 0.0, 0.0) % Supersonic outlet boundary marker(s) (NONE = no marker) MARKER_SUPERSONIC_OUTLET = ( Outlet ) %  SURFACES IDENTIFICATION % % Marker(s) of the surface to be plotted or designed MARKER_PLOTTING = ( Wall ) % Marker(s) of the surface where the functional (Cd, Cl, etc.) will be evaluated MARKER_MONITORING = ( Wall ) %  COMMON PARAMETERS DEFINING THE NUMERICAL METHOD % % % Numerical method for spatial gradients (GREEN_GAUSS, LEAST_SQUARES, % WEIGHTED_LEAST_SQUARES) NUM_METHOD_GRAD= WEIGHTED_LEAST_SQUARES % % CourantFriedrichsLewy condition of the finest grid CFL_NUMBER= 2 % % Adaptive CFL number (NO, YES) CFL_ADAPT= NO % % Parameters of the adaptive CFL number (factor down, factor up, CFL min value, % CFL max value ) CFL_ADAPT_PARAM= ( 0.1, 2.0, 1, 1e10 ) % % RungeKutta alpha coefficients RK_ALPHA_COEFF= ( 0.66667, 0.66667, 1.000000 ) % % Number of total iterations ITER= 5000 % % Linear solver for the implicit formulation (BCGSTAB, FGMRES) LINEAR_SOLVER= FGMRES % % Preconditioner of the Krylov linear solver (ILU, JACOBI, LINELET, LU_SGS) LINEAR_SOLVER_PREC= ILU % % Min error of the linear solver for the implicit formulation LINEAR_SOLVER_ERROR= 1E6 % % Max number of iterations of the linear solver for the implicit formulation LINEAR_SOLVER_ITER= 20 %  MULTIGRID PARAMETERS % % MultiGrid Levels (0 = no multigrid) MGLEVEL = 0 % Multigrid cycle (V_CYCLE, W_CYCLE, FULLMG_CYCLE) MGCYCLE = W_CYCLE % Multigrid presmoothing level MG_PRE_SMOOTH = ( 1, 2, 3, 3 ) % Multigrid postsmoothing level MG_POST_SMOOTH = ( 0, 0, 0, 0 ) % Jacobi implicit smoothing of the correction MG_CORRECTION_SMOOTH = ( 0, 0, 0, 0 ) % Damping factor for the residual restriction MG_DAMP_RESTRICTION = 1.0 % Damping factor for the correction prolongation MG_DAMP_PROLONGATION = 1.0 %  FLOW NUMERICAL METHOD DEFINITION % % % Convective numerical method (JST, LAXFRIEDRICH, CUSP, ROE, AUSM, HLLC, % TURKEL_PREC, MSW) CONV_NUM_METHOD_FLOW= HLLC % % Monotonic Upwind Scheme for Conservation Laws (TVD) in the flow equations. % Required for 2nd order upwind schemes (NO, YES) MUSCL_FLOW= YES % % Slope limiter (NONE, VENKATAKRISHNAN, VENKATAKRISHNAN_WANG, % BARTH_JESPERSEN, VAN_ALBADA_EDGE) SLOPE_LIMITER_FLOW= NONE % % Coefficient for the limiter (smooth regions) VENKAT_LIMITER_COEFF= 0.006 % % 2nd and 4th order artificial dissipation coefficients JST_SENSOR_COEFF= ( 0.5, 0.02 ) % % Time discretization (RUNGEKUTTA_EXPLICIT, EULER_IMPLICIT, EULER_EXPLICIT) TIME_DISCRE_FLOW= RUNGEKUTTA_EXPLICIT %  CONVERGENCE PARAMETERS % % % Convergence criteria (CAUCHY, RESIDUAL) CONV_FIELD= RMS_DENSITY % % Min value of the residual (log10 of the residual) CONV_RESIDUAL_MINVAL= 13 % % Start convergence criteria at iteration number CONV_STARTITER= 10 % % Number of elements to apply the criteria CONV_CAUCHY_ELEMS= 100 % % Epsilon to control the series convergence CONV_CAUCHY_EPS= 1E10 %  INPUT/OUTPUT INFORMATION % % Mesh input file MESH_FILENAME = triangless.su2 %Mesh input file format (SU2, CGNS, NETCDF_ASCII) MESH_FORMAT = SU2 % Mesh output file MESH_OUT_FILENAME = my_mesh_out.su2 % Restart flow input file SOLUTION_FILENAME = restart.dat % Output file format (PARAVIEW, TECPLOT, STL) OUTPUT_FILES = PARAVIEW_ASCII % Output file convergence history (w/o extension) CONV_FILENAME = history % Output file restart flow RESTART_FILENAME = restart.dat % Output file flow (w/o extension) variables VOLUME_FILENAME = Flow_OS % Output file surface flow coefficient (w/o extension) SURFACE_FILENAME = surface % Writing solution file frequency WRT_SOL_FREQ = 100 % Writing convergence history frequency WRT_CON_FREQ = 1 

August 28, 2020, 02:56 

#2 
Senior Member
Pedro Gomes
Join Date: Dec 2017
Posts: 466
Rep Power: 13 
Use EULER_IMPLICIT instead of RK explicit.
Use the VENKATAKRISHNAN_WANG limiter with coeff ~0.05 or the VAN_ALBADA_EDGE. I don't have much experience with very high speed flows, but you may also try other schemes like AUSM+up or SLAU (if you do set USE_ACCURATE_FLUX_JACOBIANS=YES as it may allow you to run at higher CFL). More info here: https://su2code.github.io/docs_v7/ConvectiveSchemes/ For a well posed problem with upwind schemes, 20 linear solver iterations is wasteful, 510 should be all you need, or linear solver tolerance 0.05 to 0.01. 

August 28, 2020, 10:39 

#3 
New Member
William Haigh
Join Date: Aug 2020
Posts: 20
Rep Power: 5 
Thank you for your tips I have tried to apply them but I was still having some errors.
Do you think I could send you the mesh I am using to take a look at it? I suspect that this might be the problem. Thanks! 

August 28, 2020, 18:15 

#4 
Senior Member
Pedro Gomes
Join Date: Dec 2017
Posts: 466
Rep Power: 13 
SU2 prints some mesh statistics and sanity checks, if you post the screen output for your case I can help you decode that information.


August 29, 2020, 12:55 

#5 
New Member
William Haigh
Join Date: Aug 2020
Posts: 20
Rep Power: 5 
This is what I obtain:
 Geometry Preprocessing ( Zone 0 )  Two dimensional problem. 14951 grid points. 14625 volume elements. 3 surface markers. 100 boundary elements in index 0 (Marker = inlet). 25 boundary elements in index 1 (Marker = outlet). 525 boundary elements in index 2 (Marker = wall). 14625 quadrilaterals. Setting point connectivity. Renumbering points (Reverse Cuthill McKee Ordering). Recomputing point connectivity. Setting element connectivity. Checking the numerical grid orientation. There has been a reorientation of 12500 QUADRILATERAL volume elements. There has been a reorientation of 650 LINE surface elements. Identifying edges and vertices. Computing centers of gravity. Setting the control volume structure. Area of the computational grid: 0.97909. Searching for the closest normal neighbors to the surfaces. Storing a mapping from global to local point index. Compute the surface curvature. Max K: 269.383. Mean K: 2.87427. Standard deviation K: 22.7089. Checking for periodicity. Computing mesh quality statistics for the dual control volumes. ++  Mesh Quality Metric Minimum Maximum ++  Orthogonality Angle (deg.) 45.0981 90  CV Face Area Aspect Ratio 1.11916 9.17412  CV SubVolume Ratio 1 6.09331 ++ 

August 30, 2020, 10:47 

#6 
Senior Member
Pedro Gomes
Join Date: Dec 2017
Posts: 466
Rep Power: 13 
Statistics look ok, it should not be a mesh problem.


August 31, 2020, 04:48 

#7 
New Member
William Haigh
Join Date: Aug 2020
Posts: 20
Rep Power: 5 
Thanks for all of your help!


January 2, 2023, 02:38 

#8 
New Member
Praveen
Join Date: May 2022
Posts: 8
Rep Power: 4 
So were you able to figure it out? what was causing the divergence and what was the solution?


January 2, 2023, 05:56 

#9 
Senior Member
bigfoot
Join Date: Dec 2011
Location: Netherlands
Posts: 545
Rep Power: 17 
If you are experiencing convergence issues, please create a new post with details of your specific case so we can help you. Also make sure to use the latest SU2 version.


Tags 
mesh, oblique shock, supersonic flow 
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