CFD Online Discussion Forums - Rising residual behaviour and convergence

Hi all,

Can anyone help me identify if the following Euler run has converged? While the CL, CD, CFz, etc. all seem to show a converged result, it is the first simulation I have seen where Res_Flow[0] – Res_Flow[4] (one attached for illustration) starts with a low residual and converges to a higher one.

Is this a Is this physicallly valid convergence? I have also pasted the contents of my configuration file below, in case I have made a simple error in my setup. I could only upload 5 files so I chose a few different plots to show what appears to be converged values. The Res_Flow values look suspicious though!

Also, what exactly are Res_Flow[0-4]? I saw another post suggesting one to look in the FAQ. While the link given doesn't work anymore, I presume it now should point to https://su2code.github.io/docs/FAQ/. The page mentions Residual[0] and Primitive[0] but not Res_Flow[0] etc. Are they just renamed variables?

Apologies if these answers have been mentioned elsewhere! Please let me know if more information is needed to diagnose this.
Kind regards,
Tim

Code:

% ------------- DIRECT, ADJOINT, AND LINEARIZED PROBLEM DEFINITION ------------%

%

% Physical governing equations (EULER, NAVIER_STOKES)

PHYSICAL_PROBLEM= EULER

%

% Mathematical problem (DIRECT, CONTINUOUS_ADJOINT)

MATH_PROBLEM= DIRECT

%

% Restart solution (NO, YES)

RESTART_SOL= NO

%

% Write binary restart files (YES, NO)

WRT_BINARY_RESTART= NO

%

% Read binary restart files (YES, NO)

READ_BINARY_RESTART= NO



% -------------------- COMPRESSIBLE FREE-STREAM DEFINITION --------------------%

%

% Mach number (non-dimensional, based on the free-stream values)

MACH_NUMBER= 1.7

%

% Angle of attack (degrees)

AOA= 0.0

%

% Side-slip angle (degrees)

SIDESLIP_ANGLE= 0.0

%

% Free-stream pressure (101325.0 N/m^2 by default, only for Euler equations)

FREESTREAM_PRESSURE= 9119.83

%

% Free-stream temperature (288.15 K by default)

FREESTREAM_TEMPERATURE= 216.65



% ---------------------- 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 yaMAIN_BOX non-dimensional moment

REF_LENGTH= 1.0

%

% Reference area for force coefficients (0 implies automatic calculation)

REF_AREA= 0

%

% Flow non-dimensionalization (DIMENSIONAL, FREESTREAM_PRESS_EQ_ONE,

%                              FREESTREAM_VEL_EQ_MACH, FREESTREAM_VEL_EQ_ONE)

REF_DIMENSIONALIZATION= FREESTREAM_VEL_EQ_ONE



% ----------------------- BOUNDARY CONDITION DEFINITION -----------------------%

%

% Marker of the Euler boundary (0 implies no marker)

MARKER_EULER= ( BODY )

%

% Marker of the far field (0 implies no marker)

MARKER_FAR= ( quad_FARFIELD, tri_FARFIELD )

%

% Marker of symmetry boundary (0 implies no marker)

MARKER_SYM= ( quad_SYMMETRY, tri_SYMMETRY )



% ------------------------ SURFACES IDENTIFICATION ----------------------------%

%

% Marker(s) of the surface in the surface flow solution file

MARKER_PLOTTING = ( BODY )

%

% Marker(s) of the surface where the non-dimensional coefficients are evaluated.

MARKER_MONITORING = ( BODY )

%

% Marker(s) of the surface where obj. func. (design problem) will be evaluated

MARKER_DESIGNING = ( BODY )



% ------------- COMMON PARAMETERS TO DEFINE THE NUMERICAL METHOD --------------%

%

% Numerical method for spatial gradients (GREEN_GAUSS, WEIGHTED_LEAST_SQUARES)

NUM_METHOD_GRAD= WEIGHTED_LEAST_SQUARES

%

% Objective function in gradient evaluation  (DRAG, LIFT, SIDEFORCE, MOMENT_X,

%                                             MOMENT_Y, MOMENT_Z, EFFICIENCY,

%                                             EQUIVALENT_AREA, NEARFIELD_PRESSURE,

%                                             FORCE_X, FORCE_Y, FORCE_Z, THRUST,

%                                             TORQUE, FREE_SURFACE, TOTAL_HEATFLUX,

%                                             MAXIMUM_HEATFLUX, INVERSE_DESIGN_PRESSURE,

%                                             INVERSE_DESIGN_HEATFLUX)

OBJECTIVE_FUNCTION= DRAG

%

% Courant-Friedrichs-Lewy condition of the finest grid

CFL_NUMBER= 5.0

%

% Adaptive CFL number (NO, YES)

CFL_ADAPT= YES

%

% Parameters of the adaptive CFL number (factor down, factor up, CFL min value,

%                                        CFL max value )

CFL_ADAPT_PARAM= ( 1.5, 0.5, 1.0, 100.0 )

%

% Runge-Kutta alpha coefficients

RK_ALPHA_COEFF= ( 0.66667, 0.66667, 1.000000 )

%

% Number of total iterations

EXT_ITER= 99999

%

% Linear solver for the implicit formulation (BCGSTAB, FGMRES)

LINEAR_SOLVER= FGMRES

%

% Preconditioner of the Krylov linear solver (ILU, LU_SGS, LINELET, JACOBI)

LINEAR_SOLVER_PREC= LU_SGS

%

% Min error of the linear solver for the implicit formulation

LINEAR_SOLVER_ERROR= 1E-6

%

% Max number of iterations of the linear solver for the implicit formulation

LINEAR_SOLVER_ITER= 2



% ----------------------- SLOPE LIMITER DEFINITION ----------------------------%

%

% Coefficient for the limiter

VENKAT_LIMITER_COEFF= 0.03

%

% Coefficient for the sharp edges limiter

ADJ_SHARP_LIMITER_COEFF= 3.0

%

% Reference coefficient (sensitivity) for detecting sharp edges.

REF_SHARP_EDGES= 3.0

%

% Remove sharp edges from the sensitivity evaluation (NO, YES)

SENS_REMOVE_SHARP= YES



% -------------------------- MULTIGRID PARAMETERS -----------------------------%

%

% Multi-Grid Levels (0 = no multi-grid)

MGLEVEL= 3

%

% Multi-grid cycle (V_CYCLE, W_CYCLE, FULLMG_CYCLE)

MGCYCLE= W_CYCLE

%

% Multi-Grid PreSmoothing Level

MG_PRE_SMOOTH= ( 1, 2, 3, 3 )

%

% Multi-Grid 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= 0.9

%

% Damping factor for the correction prolongation

MG_DAMP_PROLONGATION= 0.9



% -------------------- FLOW NUMERICAL METHOD DEFINITION -----------------------%

%

% Convective numerical method (JST, LAX-FRIEDRICH, CUSP, ROE, AUSM, HLLC,

%                              TURKEL_PREC, MSW)

CONV_NUM_METHOD_FLOW= JST

%

% 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

%

% 2nd and 4th order artificial dissipation coefficients

JST_SENSOR_COEFF= ( 0.5, 0.02 )

%

% Time discretization (RUNGE-KUTTA_EXPLICIT, EULER_IMPLICIT, EULER_EXPLICIT)

TIME_DISCRE_FLOW= EULER_IMPLICIT



% ---------------- ADJOINT-FLOW NUMERICAL METHOD DEFINITION -------------------%

%

% Convective numerical method (JST, LAX-FRIEDRICH, ROE)

CONV_NUM_METHOD_ADJFLOW= JST

%

% Monotonic Upwind Scheme for Conservation Laws (TVD) in the adjoint flow equations.

%           Required for 2nd order upwind schemes (NO, YES)

MUSCL_ADJFLOW= YES

%

% Slope limiter (NONE, VENKATAKRISHNAN, BARTH_JESPERSEN, VAN_ALBADA_EDGE,

%                SHARP_EDGES, WALL_DISTANCE)

SLOPE_LIMITER_ADJFLOW= NONE

%

% 2nd, and 4th order artificial dissipation coefficients

ADJ_JST_SENSOR_COEFF= ( 0.0, 0.02 )

%

% Reduction factor of the CFL coefficient in the adjoint problem

CFL_REDUCTION_ADJFLOW= 0.5

%

% Time discretization (RUNGE-KUTTA_EXPLICIT, EULER_IMPLICIT)

TIME_DISCRE_ADJFLOW= EULER_IMPLICIT



% --------------------------- CONVERGENCE PARAMETERS --------------------------&

%

% Convergence criteria (CAUCHY, RESIDUAL)

CONV_CRITERIA= RESIDUAL

%

% Residual reduction (order of magnitude with respect to the initial value)

RESIDUAL_REDUCTION= 8

%

% Min value of the residual (log10 of the residual)

RESIDUAL_MINVAL= -12

%

% Start convergence criteria at iteration number

STARTCONV_ITER= 25

%

% Number of elements to apply the criteria

CAUCHY_ELEMS= 100

%

% Epsilon to control the series convergence

CAUCHY_EPS= 1E-10

%

% Function to apply the criteria (LIFT, DRAG, NEARFIELD_PRESS, SENS_GEOMETRY, 

%                                            SENS_MACH, DELTA_LIFT, DELTA_DRAG)

CAUCHY_FUNC_FLOW= DRAG



% ------------------------- INPUT/OUTPUT INFORMATION --------------------------%

%

% Mesh input file

MESH_FILENAME= ../1_mesh/delta-split-mixed-000a-170m-156s-bc-adf.cgns

%

% Mesh output file

MESH_OUT_FILENAME= mesh_out.su2

%

% Restart flow input file

SOLUTION_FLOW_FILENAME= solution_flow.dat

%

% Restart adjoint input file

SOLUTION_ADJ_FILENAME= solution_adj.dat

%

% Mesh input file format (SU2)

MESH_FORMAT= CGNS

%

% Output file format (PARAVIEW, TECPLOT)

OUTPUT_FORMAT= PARAVIEW

%

% Output file convergence history

CONV_FILENAME= history

%

% Output file restart flow

RESTART_FLOW_FILENAME= restart_flow.dat

%

% Output file restart adjoint

RESTART_ADJ_FILENAME= restart_adj.dat

%

% Output file flow (w/o extension) variables

VOLUME_FLOW_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_FLOW_FILENAME= surface_flow

%

% Output file surface adjoint coefficient (w/o extension)

SURFACE_ADJ_FILENAME= surface_adjoint

%

% Writing solution frequency

WRT_SOL_FREQ= 100

%

% Writing convergence history frequency

WRT_CON_FREQ= 1