[Amber0922]

Hi,
I recently ran an unsteady simulation of a backward-facing step, but it diverged after 2993 steps with the error message "SU2 has diverged (NaN detected)" in the function "void CSolver::SetResidual_RMS(const CGeometry*, const CConfig*)". I have tried modifying my configuration, but to no avail. Could you please help me identify what went wrong? Thank you so much for your time and assistance.


% ------------- DIRECT, ADJOINT, AND LINEARIZED PROBLEM DEFINITION ------------%
%
% Physical governing equations (EULER, NAVIER_STOKES,
% WAVE_EQUATION, HEAT_EQUATION, FEM_ELASTICITY,
% POISSON_EQUATION)
SOLVER= RANS
KIND_TURB_MODEL= SA
HYBRID_RANSLES= SA_EDDES
%
% Mathematical problem (DIRECT, CONTINUOUS_ADJOINT)
MATH_PROBLEM= DIRECT
%
% Axisymmetric simulation, only compressible flows (NO, YES)
AXISYMMETRIC= NO
%
% Restart solution (NO, YES)
RESTART_SOL= NO
%
% System of measurements (SI, US)
% International system of units (SI): ( meters, kilograms, Kelvins,
% Newtons = kg m/s^2, Pascals = N/m^2,
% Density = kg/m^3, Speed = m/s,
% Equiv. Area = m^2 )
% United States customary units (US): ( inches, slug, Rankines, lbf = slug ft/s^2,
% psf = lbf/ft^2, Density = slug/ft^3,
% Speed = ft/s, Equiv. Area = ft^2 )
SYSTEM_MEASUREMENTS= SI
%
% ----------- COMPRESSIBLE AND INCOMPRESSIBLE FREE-STREAM DEFINITION ----------%
%
MACH_NUMBER= 0.128
AOA= 0.0
SIDESLIP_ANGLE= 0.0
FREESTREAM_TEMPERATURE= 289
FREESTREAM_VELOCITY= ( 44.2, 0.00, 0.00 )
REYNOLDS_NUMBER= 36000
REYNOLDS_LENGTH= 0.0127
%
% ---------------------- 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 non-dimensional moment
REF_LENGTH= 1
%
% Reference area for force coefficients (0 implies automatic calculation)
REF_AREA= 0
%
% ------------------------- UNSTEADY SIMULATION -------------------------------%

TIME_DOMAIN= YES
TIME_MARCHING= DUAL_TIME_STEPPING-2ND_ORDER
TIME_STEP= 3E-6
%MAX_TIME= 9E-2
UNST_CFL_NUMBER= 0.0
INNER_ITER= 30
TIME_ITER = 10000
% Iteration number to begin unsteady restarts
RESTART_ITER= 1000
%Time iteration to start the windowed time average in a direct run
WINDOW_START_ITER = 200
% Window used for reverse sweep and direct run. Options (SQUARE, HANN, HANN_SQUARE, BUMP) Square is default.
WINDOW_FUNCTION = SQUARE
%
% -------------------- BOUNDARY CONDITION DEFINITION --------------------------%
%
% Navier-Stokes wall boundary marker(s) (NONE = no marker)
MARKER_HEATFLUX= ( STEP, 0.0, UPPERWALL,0.0, LOWERWALL,0.0 )
%
% Read inlet profile from a file (YES, NO) default: NO
SPECIFIED_INLET_PROFILE= NO
%
% File specifying inlet profile
INLET_FILENAME= inlet.dat
%
% Far-field boundary marker(s) (NONE = no marker)
MARKER_FAR= ( FARIN )
%
% Pressure outlet marker
MARKER_OUTLET= ( FAROUT, 96305.5)
%
% Periodic boundary marker(s) (NONE = no marker)
% Format: ( periodic marker, donor marker, rotation_center_x, rotation_center_y,
% rotation_center_z, rotation_angle_x-axis, rotation_angle_y-axis,
% rotation_angle_z-axis, translation_x, translation_y, translation_z, ... )
MARKER_PERIODIC= ( WALL1, WALL2,0, 0, 0, 0, 0, 0, 0, 0, -0.0254 )
%
% Marker(s) of the surface to be plotted or designed
MARKER_PLOTTING= ( STEP, WALL1, WALL2, UPPERWALL, LOWERWALL)
%
% Marker(s) of the surface where the functional (Cd, Cl, etc.) will be evaluated
MARKER_MONITORING= ( FAROUT,STEP, WALL1, WALL2, UPPERWALL, LOWERWALL,FARIN)

% ------------- COMMON PARAMETERS DEFINING THE NUMERICAL METHOD ---------------%
%
% Numerical method for spatial gradients (GREEN_GAUSS, WEIGHTED_LEAST_SQUARES)
NUM_METHOD_GRAD= WEIGHTED_LEAST_SQUARES
%
% Courant-Friedrichs-Lewy condition of the finest grid
CFL_NUMBER= 0.5
%
% 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= ( 1.5, 0.5, 2.0, 100.0 )
%
% Runge-Kutta alpha coefficients
RK_ALPHA_COEFF= ( 0.66667, 0.66667, 1.000000 )

%

% ----------------------- SLOPE LIMITER DEFINITION ----------------------------%
%
VENKAT_LIMITER_COEFF= 0.1
ADJ_SHARP_LIMITER_COEFF= 3.0
REF_SHARP_EDGES= 3.0
SENS_REMOVE_SHARP= NO

% -------------------- FLOW NUMERICAL METHOD DEFINITION -----------------------%
%
CONV_NUM_METHOD_FLOW= ROE
MUSCL_FLOW= YES
SLOPE_LIMITER_FLOW= VENKATAKRISHNAN
JST_SENSOR_COEFF= ( 0.5, 0.02 )
TIME_DISCRE_FLOW= EULER_IMPLICIT
%
% ------------------------ LINEAR SOLVER DEFINITION ---------------------------%
%
% Linear solver or smoother for implicit formulations (BCGSTAB, FGMRES, SMOOTHER_JACOBI,
% SMOOTHER_ILU, SMOOTHER_LUSGS,
% SMOOTHER_LINELET)
LINEAR_SOLVER= FGMRES
%
% Preconditioner of the Krylov linear solver (ILU, LU_SGS, LINELET, JACOBI)
% LINEAR_SOLVER_PREC= LU_SGS
%
% Linael solver ILU preconditioner fill-in level (0 by default)
% LINEAR_SOLVER_ILU_FILL_IN= 0
%
% Minimum error of the linear solver for implicit formulations
LINEAR_SOLVER_ERROR= 0.1
%
% Max number of iterations of the linear solver for the implicit formulation
LINEAR_SOLVER_ITER= 5
%
% ----------------------------------- END -------------------------------------%
%
% -------------------- TURBULENT NUMERICAL METHOD DEFINITION ------------------%
%
CONV_NUM_METHOD_TURB= SCALAR_UPWIND
TIME_DISCRE_TURB= EULER_IMPLICIT

% --------------------------- CONVERGENCE PARAMETERS --------------------------%
%
CONV_RESIDUAL_MINVAL= -10
CONV_STARTITER= 10
CONV_CAUCHY_ELEMS= 100
CONV_CAUCHY_EPS= 1E-5
%
%DV_KIND= SCALE_GRID
%DV_MARKER= ( WALL1, WALL2, INLET, STEP, OUTLET, UPPERWALL, LOWERWALL )
%DV_PARAM= ( 1.0 )
%DV_VALUE = 0.01


OUTPUT_FILES= (RESTART, TECPLOT)
% list of writing frequencies corresponding to the list in OUTPUT_FILES
OUTPUT_WRT_FREQ= 30, 20
% ------------------------- INPUT/OUTPUT INFORMATION --------------------------%
%
% Mesh input file
MESH_FILENAME= backwardstep.cgns
%
% Mesh input file format (SU2, CGNS, NETCDF_ASCII)
MESH_FORMAT= CGNS
%
% Mesh output file
MESH_OUT_FILENAME= mesh_out.su2
%
% Restart flow input file
SOLUTION_FILENAME= solution_flow.dat
%
% Restart adjoint input file
SOLUTION_ADJ_FILENAME= solution_adj.dat
%
% Output file format (PARAVIEW, TECPLOT, STL)
TABULAR_FORMAT= TECPLOT
%
% Output file convergence history (w/o extension)
CONV_FILENAME= history
%
% Output file restart flow
RESTART_FILENAME= restart_flow.dat
%
% Output file restart adjoint
RESTART_ADJ_FILENAME= restart_adj.dat
%
% Output file flow (w/o extension) variables
VOLUME_OUTPUT=(MEAN_PRESSURE， MEAN_VELOCITY-X, MEAN_VELOCITY-Y, MEAN_VELOCITY-Z, MEAN_DENSITY ,MACH)
VOLUME_FILENAME= flow
%
% Output file adjoint (w/o extension) variables
VOLUME_ADJ_FILENAME= adjoint
%
% Output objective function gradient (using continuous adjoint)
GRAD_OBJFUNC_FILENAME= of_grad.dat
%
% Output file surface flow coefficient (w/o extension)
SURFACE_FILENAME= surface_flow
%
% Output file surface adjoint coefficient (w/o extension)
SURFACE_ADJ_FILENAME= surface_adjoint
%
%
% Screen output
%SCREEN_OUTPUT=(TIME_ITER, INNER_ITER, LIFT, DRAG, TOTAL_HEATFLUX)
SCREEN_OUTPUT=(ITER, MAX_NU_TILDE, RMS_RES)

[bigfootedrockmidget]

Do the inner iterations converge? What is the flow supposed to do, show a turbulent vortex shedding behind the step? Do you already see some correct physics or it's still a big mess?

[Amber0922]

Originally Posted by bigfootedrockmidget

Do the inner iterations converge? What is the flow supposed to do, show a turbulent vortex shedding behind the step? Do you already see some correct physics or it's still a big mess?

The inner iteration has diverged, resulting in unexpected flow performance. Should I decrease the time step or increase the number of inner iterations?