Register Blogs Members List Search Today's Posts Mark Forums Read June 13, 2023, 00:37 Unsteady simulated divergence #1 Member   Zhang Join Date: Mar 2023 Posts: 66 Rep Power: 2 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)   June 13, 2023, 10:27 #2 Senior Member   bigfoot Join Date: Dec 2011 Location: Netherlands Posts: 377 Rep Power: 16 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?   June 15, 2023, 06:12 #3
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Zhang
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 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?  Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules Similar Threads Thread Thread Starter Forum Replies Last Post chittipo FLUENT 164 November 18, 2023 12:54 Kieyo Fluent Multiphase 0 November 10, 2022 00:58 moabdi FLUENT 0 June 23, 2016 12:30 hugocis Main CFD Forum 2 June 10, 2010 05:24 Christoph_84 FLUENT 0 February 25, 2010 12:06

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