[ander]

I have tried becoming familiar with SU2 lately, but I am struggling a lot to get convergent results in general.
I tried setting up a very simple 2D cylinder flow case, and I would be happy to get some input as to why it's not converging. If I'm unable to run simple case like this successfully don't see how I will be ever able to run more complicated cases My impression is that these kinds of opensource codes are much harder to converge than for instance ansys, and I wonder why that is the case.

The triangular mesh is generated in salome, and converted to .su2 format with a python script.
With the current settings, density rms reached a minimum value of about -1.5.
Navier stokes equations are being solved and farfield boundaries are used.

I added a picture of the mesh and the mesh quality statistics.
Config options are pasted below:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Autogenerated config file
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Physical governing equations (EULER, NAVIER_STOKES,WAVE_EQUATION, HEAT_EQUATION, FEM_ELASTICITY,POISSON_EQUATION)
SOLVER= NAVIER_STOKES
KIND_TURB_MODEL= NONE
MATH_PROBLEM= DIRECT
RESTART_SOL= NO


% -------------------- COMPRESSIBLE FREE-STREAM DEFINITION --------------------
MACH_NUMBER= 2
AOA= 0.0
SIDESLIP_ANGLE= 0.0
INIT_OPTION= TD_CONDITIONS
FREESTREAM_OPTION= TEMPERATURE_FS
FREESTREAM_TEMPERATURE= 288.15
FREESTREAM_PRESSURE= 101325.0

% ---- IDEAL GAS, POLYTROPIC, VAN DER WAALS AND PENG ROBINSON CONSTANTS -------
FLUID_MODEL= STANDARD_AIR

% --------------------------- VISCOSITY MODEL ---------------------------------
VISCOSITY_MODEL= SUTHERLAND

% --------------------------- THERMAL CONDUCTIVITY MODEL ----------------------
CONDUCTIVITY_MODEL= CONSTANT_PRANDTL

% ---------------------- REFERENCE VALUE DEFINITION ---------------------------
REF_ORIGIN_MOMENT_X= 0.25
REF_ORIGIN_MOMENT_Y= 0.0
REF_ORIGIN_MOMENT_Z= 0.0
REF_LENGTH= 1.0
REF_AREA= 1.0
REF_DIMENSIONALIZATION= DIMENSIONAL

% -------------------- BOUNDARY CONDITION DEFINITION --------------------------
MARKER_HEATFLUX= (projectile,0.0)
MARKER_EULER= NONE
MARKER_FAR= (farfield,outlet)
INLET_TYPE= MASS_FLOW
MARKER_INLET= NONE
MARKER_OUTLET= NONE
MARKER_SUPERSONIC_INLET= NONE
MARKER_SUPERSONIC_OUTLET= NONE
MARKER_SYM= NONE
MARKER_PLOTTING= projectile
MARKER_MONITORING= projectile

% ------------- COMMON PARAMETERS DEFINING THE NUMERICAL METHOD ---------------
NUM_METHOD_GRAD= GREEN_GAUSS
CFL_NUMBER= 20
CFL_ADAPT= NO
INNER_ITER= 1000

% ------------------------ LINEAR SOLVER DEFINITION ---------------------------
LINEAR_SOLVER= FGMRES
LINEAR_SOLVER_PREC= ILU
LINEAR_SOLVER_ERROR= 1e-10
LINEAR_SOLVER_ITER= 10

% -------------------------- MULTIGRID PARAMETERS -----------------------------
MGLEVEL= 0

% -------------------- FLOW NUMERICAL METHOD DEFINITION -----------------------
CONV_NUM_METHOD_FLOW= ROE
ENTROPY_FIX_COEFF= 0.01
JST_SENSOR_COEFF= ( 0.5, 0.02 )
MUSCL_FLOW= YES
SLOPE_LIMITER_FLOW= VENKATAKRISHNAN
VENKAT_LIMITER_COEFF= 0.05
TIME_DISCRE_FLOW= EULER_IMPLICIT
USE_ACCURATE_FLUX_JACOBIANS= YES

% -------------------- TURBULENT NUMERICAL METHOD DEFINITION ------------------
CONV_NUM_METHOD_TURB= SCALAR_UPWIND
MUSCL_TURB= NO
SLOPE_LIMITER_TURB= VENKATAKRISHNAN
TIME_DISCRE_TURB= EULER_IMPLICIT

% --------------------------- CONVERGENCE PARAMETERS --------------------------
CONV_FIELD= RMS_DENSITY
CONV_RESIDUAL_MINVAL= -5
CONV_STARTITER= 10

% ------------------------- INPUT/OUTPUT INFORMATION --------------------------
MESH_FILENAME= /home/anders/dev/CFD-Traject/Tests/2Dcylinder/2Dcyl.su2
MESH_FORMAT= SU2
MESH_OUT_FILENAME= /home/anders/dev/CFD-Traject/Tests/2Dcylinder/configuration_0/flow_output/mesh_out.su2
SOLUTION_FILENAME= solution_flow.dat
TABULAR_FORMAT= CSV
CONV_FILENAME= /home/anders/dev/CFD-Traject/Tests/2Dcylinder/configuration_0/flow_output/history
RESTART_FILENAME= /home/anders/dev/CFD-Traject/Tests/2Dcylinder/configuration_0/flow_output/restart_flow.dat
VOLUME_FILENAME= /home/anders/dev/CFD-Traject/Tests/2Dcylinder/configuration_0/flow_output/flow
SURFACE_FILENAME= /home/anders/dev/CFD-Traject/Tests/2Dcylinder/configuration_0/flow_output/surface_flow
SCREEN_OUTPUT= ( INNER_ITER, WALL_TIME, REL_RMS_DENSITY, RMS_DENSITY, LIFT, DRAG )
HISTORY_OUTPUT= ( INNER_ITER, REL_RMS_DENSITY, RMS_DENSITY, LIFT, DRAG )

[ander]

attachments

[pcg]

What is the diameter? Is this supposed to be laminar? And if so, is it supposed to be steady state?

[ander]

Originally Posted by pcg

What is the diameter? Is this supposed to be laminar? And if so, is it supposed to be steady state?

The diameter is 1m, but the point was not really to try and model viscous effects. I was looking for a steady solution. I changed the solver to EULER to simplify things and eliminate the potential for vortex shredding, but still, the solution doesn't converge. It stops converging at density rms = -0.35.

[pcg]

Inviscid flow is not potential flow, it will still separate and become unsteady, just in an unphysical way.
If you want any steady solution around a cylinder you need conditions and models that give you steady state.

[ander]

Ahh, that was clarifying to hear, thanks! I tried the pseudo time stepping of 1st order and it gave me good convergence for the navier stokes equations, however the Euler equations still flatline at density rms = -0.75. Not really sure what I can do to make the latter case work though. Anyhow I will probably use the time domain stepping as my default setup from now since it seems more robust, but please correct me if that's a dumb idea.

Here is my cfg file for the Euler problem as reference:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Autogenerated config file
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Physical governing equations (EULER, NAVIER_STOKES,WAVE_EQUATION, HEAT_EQUATION, FEM_ELASTICITY,POISSON_EQUATION)
SOLVER= EULER
KIND_TURB_MODEL= SA
MATH_PROBLEM= DIRECT
RESTART_SOL= NO

% ------------------------- UNSTEADY SIMULATION -------------------------------
TIME_DOMAIN= YES
TIME_MARCHING= DUAL_TIME_STEPPING-1ST_ORDER
UNST_CFL_NUMBER= 3000
TIME_STEP= 0
MAX_TIME= 1
TIME_ITER= 1000

% -------------------- COMPRESSIBLE FREE-STREAM DEFINITION --------------------
MACH_NUMBER= 2
AOA= 0.0
SIDESLIP_ANGLE= 0.0
INIT_OPTION= TD_CONDITIONS
FREESTREAM_OPTION= TEMPERATURE_FS
FREESTREAM_TEMPERATURE= 288.15
FREESTREAM_PRESSURE= 101325.0

% ---- IDEAL GAS, POLYTROPIC, VAN DER WAALS AND PENG ROBINSON CONSTANTS -------
FLUID_MODEL= STANDARD_AIR

% --------------------------- VISCOSITY MODEL ---------------------------------
VISCOSITY_MODEL= SUTHERLAND

% --------------------------- THERMAL CONDUCTIVITY MODEL ----------------------
CONDUCTIVITY_MODEL= CONSTANT_PRANDTL

% ---------------------- REFERENCE VALUE DEFINITION ---------------------------
REF_ORIGIN_MOMENT_X= 0.25
REF_ORIGIN_MOMENT_Y= 0.0
REF_ORIGIN_MOMENT_Z= 0.0
REF_LENGTH= 1.0
REF_AREA= 1.0
REF_DIMENSIONALIZATION= DIMENSIONAL

% -------------------- BOUNDARY CONDITION DEFINITION --------------------------
MARKER_HEATFLUX= ( NONE, 0.0 )
MARKER_EULER= projectile
MARKER_FAR= (farfield,outlet)

MARKER_PLOTTING= projectile
MARKER_MONITORING= projectile

% ------------- COMMON PARAMETERS DEFINING THE NUMERICAL METHOD ---------------
NUM_METHOD_GRAD= GREEN_GAUSS
CFL_NUMBER= 40
CFL_ADAPT= YES
CFL_ADAPT_PARAM= ( 0.1, 2.0, 1.0, 10000000000.0 )
INNER_ITER= 7

% ------------------------ LINEAR SOLVER DEFINITION ---------------------------
LINEAR_SOLVER= FGMRES
LINEAR_SOLVER_PREC= LU_SGS
LINEAR_SOLVER_ERROR= 0.0001
LINEAR_SOLVER_ITER= 7

% -------------------------- MULTIGRID PARAMETERS -----------------------------
MGLEVEL= 0

% -------------------- FLOW NUMERICAL METHOD DEFINITION -----------------------
CONV_NUM_METHOD_FLOW= ROE
ENTROPY_FIX_COEFF= 0.01
JST_SENSOR_COEFF= ( 0.5, 0.02 )
MUSCL_FLOW= YES
SLOPE_LIMITER_FLOW= VENKATAKRISHNAN
VENKAT_LIMITER_COEFF= 0.05
TIME_DISCRE_FLOW= EULER_IMPLICIT
USE_ACCURATE_FLUX_JACOBIANS= YES



% --------------------------- CONVERGENCE PARAMETERS --------------------------
CONV_FIELD= REL_RMS_DENSITY
CONV_RESIDUAL_MINVAL= -3
CONV_STARTITER= 10