# Rising residual behaviour and convergence

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#1
New Member

Tim Jim
Join Date: Sep 2017
Posts: 25
Rep Power: 4 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  Res_Flow (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 and Primitive but not Res_Flow etc. Are they just renamed variables?

Kind regards,
Tim

Code:
```% ------------- DIRECT, ADJOINT, AND LINEARIZED PROBLEM DEFINITION ------------%
%
% Physical governing equations (EULER, NAVIER_STOKES)
PHYSICAL_PROBLEM= EULER
%
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)

% -------------------- 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 of symmetry boundary (0 implies no marker)

% ------------------------ 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)
%
% 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)
%
% 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
%
% 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,
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)
%
% Monotonic Upwind Scheme for Conservation Laws (TVD) in the adjoint flow equations.
%           Required for 2nd order upwind schemes (NO, YES)
%
% Slope limiter (NONE, VENKATAKRISHNAN, BARTH_JESPERSEN, VAN_ALBADA_EDGE,
%                SHARP_EDGES, WALL_DISTANCE)
%
% 2nd, and 4th order artificial dissipation coefficients
%
% Reduction factor of the CFL coefficient in the adjoint problem
%
% Time discretization (RUNGE-KUTTA_EXPLICIT, 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 output file
MESH_OUT_FILENAME= mesh_out.su2
%
% Restart flow input file
SOLUTION_FLOW_FILENAME= solution_flow.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 flow (w/o extension) variables
VOLUME_FLOW_FILENAME= flow
%
% Output file adjoint (w/o extension) variables
%
%
% Output file surface flow coefficient (w/o extension)
SURFACE_FLOW_FILENAME= surface_flow
%
% Output file surface adjoint coefficient (w/o extension)
%
% Writing solution frequency
WRT_SOL_FREQ= 100
%
% Writing convergence history frequency
WRT_CON_FREQ= 1```
Attached Images CD.png (31.1 KB, 22 views) CFz.png (25.5 KB, 22 views) Res_Flow.png (31.4 KB, 22 views) CFL_Number.png (25.4 KB, 19 views) Res_Flow.png (24.0 KB, 19 views)  Tags configuration file, convergence, euler, residual 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 dinonettis OpenFOAM Running, Solving & CFD 10 September 13, 2018 10:22 Dan709 STAR-CCM+ 4 May 3, 2017 18:06 aja1345 FLUENT 6 November 4, 2015 02:50 plunge11 FLUENT 1 April 6, 2011 09:15 PrandtlGlawert FLUENT 1 August 13, 2009 18:06

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