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-   -   Incompressible NS cfg for an airfoil (https://www.cfd-online.com/Forums/su2/195465-incompressible-ns-cfg-airfoil.html)

Amir Adib November 8, 2017 06:24

Incompressible NS cfg for an airfoil diverges
 
Hi all,

I am trying to simulate the incompressible Navier-Stokes flow around an airfoil, with airspeed of 10 m/s (AoA=0), SA turbulence model. The chord is 3 m. I have tried many configurations and tried the solutions for similar cases on the forum, but the solution diverges each time.

I would also like to know the difference of solving this case with compressible configuration with M=0.029 (because I tried this and I get strange results, around iteration number 12000 Cl & Cd both =0.1, but maybe there is something I am doing wrong in the cfg file -it is as the incompressible cfg but without the incomp conditions and with the M, AoA & Re).

Code:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                              %
% SU2 configuration file                                                      %
% Case description: Steady incompressible laminar flow around a cylinder      %
% Author: Francisco Palacios                                                                          %
% Institution: Stanford University                                            %
% Date: 2012.03.14                                                            %
% File Version 5.0.0 "Raven"                                                %
%                                                                              %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% ------------- DIRECT, ADJOINT, AND LINEARIZED PROBLEM DEFINITION ------------%
%
% Physical governing equations (EULER, NAVIER_STOKES,
%                              WAVE_EQUATION, HEAT_EQUATION, FEM_ELASTICITY,
%                              POISSON_EQUATION)                         
PHYSICAL_PROBLEM= NAVIER_STOKES
%
% Regime type (COMPRESSIBLE, INCOMPRESSIBLE, FREESURFACE)
REGIME_TYPE= INCOMPRESSIBLE
%
% If Navier-Stokes, kind of turbulent model (NONE, SA)
KIND_TURB_MODEL= SA
%
% Mathematical problem (DIRECT, CONTINUOUS_ADJOINT)
MATH_PROBLEM= DIRECT
%
% Restart solution (NO, YES)
RESTART_SOL= NO

% -------------------- INCOMPRESSIBLE FREE-STREAM DEFINITION ------------------%
%
% Free-stream density (1.2886 Kg/m^3 (air), 998.2 Kg/m^3 (water))
FREESTREAM_DENSITY= 1.2886
%
% Free-stream velocity (m/s)
FREESTREAM_VELOCITY= ( 10.0, 0.00, 0.00 )
%
% Free-stream viscosity (1.853E-5 Ns/m^2 (air), 0.798E-3 Ns/m^2 (water))
FREESTREAM_VISCOSITY= 1.853E-5

% ---------------------- REFERENCE VALUE DEFINITION ---------------------------%
%
% Reference element length for computing the slope limiter epsilon
REF_ELEM_LENGTH= 0.1
%
% Reference origin for moment computation
REF_ORIGIN_MOMENT_X = 0.75
REF_ORIGIN_MOMENT_Y = 0.00
REF_ORIGIN_MOMENT_Z = 0.00
%
% Reference length for pitching, rolling, and yawing non-dimensional moment
REF_LENGTH_MOMENT= 3.0
%
% Reference area for force coefficients (0 implies automatic calculation)
REF_AREA= 3.0

% -------------------- BOUNDARY CONDITION DEFINITION --------------------------%
%
% Navier-Stokes wall boundary marker(s) (NONE = no marker)
MARKER_HEATFLUX= ( FOIL, 0.0 )
%
% Farfield boundary marker(s) (NONE = no marker)
MARKER_FAR= ( FAR_FIELD , OUT )
%
%
% Inlet boundary marker(s) (NONE = no marker)
% Format: ( inlet marker, total temperature, total pressure, flow_direction_x,
%          flow_direction_y, flow_direction_z, ... ) where flow_direction is
%          a unit vector.
%Incompressible: (inlet marker, NULL, velocity magnitude, flow_direction_x, flow_direction_y, flow_direction_z, ... ) where flow_direction is a unit vector.
% Default: Mach ~ 0.1
% Farfield boundary marker(s) (NONE = no marker)
%MARKER_INLET= ( FAR_FIELD , 1.2886, 10, 1.0, 0.0, 0.0  )
%
% Outlet boundary marker(s) (NONE = no marker)
% Format: ( outlet marker, back pressure (static), ... )
%MARKER_OUTLET= ( OUT, 101325.0 )
%
%
% Marker(s) of the surface to be plotted or designed
MARKER_PLOTTING= ( FOIL )
%
% Marker(s) of the surface where the functional (Cd, Cl, etc.) will be evaluated
MARKER_MONITORING= ( FOIL )

% ------------- 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= 10
%
% 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, 0.5, 100.0 )
%
% Runge-Kutta alpha coefficients
RK_ALPHA_COEFF= ( 0.66667, 0.66667, 1.000000 )
%
% Number of total iterations
EXT_ITER= 99999

% -------------------------- MULTIGRID PARAMETERS -----------------------------%
%
% Multi-Grid Levels (0 = no multi-grid)
MGLEVEL= 0
%
% Multi-grid cycle (V_CYCLE, W_CYCLE, FULLMG_CYCLE)
MGCYCLE= V_CYCLE
%
% Multi-grid pre-smoothing level
MG_PRE_SMOOTH= ( 1, 2, 2, 3, 3 )
%
% Multi-grid post-smoothing 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= 0.95
%
% Damping factor for the correction prolongation
MG_DAMP_PROLONGATION= 0.95

% -------------------- FLOW NUMERICAL METHOD DEFINITION -----------------------%
%
% Convective numerical method (JST, LAX-FRIEDRICH, CUSP, ROE, AUSM, HLLC,
%                              TURKEL_PREC, MSW)
CONV_NUM_METHOD_FLOW= ROE
%
% Spatial numerical order integration (1ST_ORDER, 2ND_ORDER, 2ND_ORDER_LIMITER)
%
SPATIAL_ORDER_FLOW= 2ND_ORDER
%
% Slope limiter (VENKATAKRISHNAN, MINMOD)
SLOPE_LIMITER_FLOW= VENKATAKRISHNAN
%
% 1st, 2nd and 4th order artificial dissipation coefficients
AD_COEFF_FLOW= ( 0.15, 0.5, 0.02 )
%
% Time discretization (RUNGE-KUTTA_EXPLICIT, EULER_IMPLICIT, EULER_EXPLICIT)
TIME_DISCRE_FLOW= EULER_IMPLICIT

% ------------------------ LINEAR SOLVER DEFINITION ---------------------------%
%
% Linear solver for the implicit formulation (BCGSTAB, FGMRES)
LINEAR_SOLVER= FGMRES
%
% Min error of the linear solver for the implicit formulation
LINEAR_SOLVER_ERROR= 1E-4
%
% Max number of iterations of the linear solver for the implicit formulation
LINEAR_SOLVER_ITER= 5
%
% -------------------- TURBULENT NUMERICAL METHOD DEFINITION ------------------%
%
% Convective numerical method (SCALAR_UPWIND)
CONV_NUM_METHOD_TURB= SCALAR_UPWIND
%
% Spatial numerical order integration (1ST_ORDER, 2ND_ORDER, 2ND_ORDER_LIMITER)
%
SPATIAL_ORDER_TURB= 1ST_ORDER
%
% Time discretization (EULER_IMPLICIT)
TIME_DISCRE_TURB= EULER_IMPLICIT


% --------------------------- CONVERGENCE PARAMETERS --------------------------%
%
% Convergence criteria (CAUCHY, RESIDUAL)
%
CONV_CRITERIA= RESIDUAL
%
% Residual reduction (order of magnitude with respect to the initial value)
RESIDUAL_REDUCTION= 6
%
% Min value of the residual (log10 of the residual)
RESIDUAL_MINVAL= -8
%
% Start convergence criteria at iteration number
STARTCONV_ITER= 10
%
% Number of elements to apply the criteria
CAUCHY_ELEMS= 100
%
% Epsilon to control the series convergence
CAUCHY_EPS= 1E-6
%
% 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= Tyran.cgns
%
% Mesh input file format (SU2, CGNS, NETCDF_ASCII)
MESH_FORMAT= CGNS
%
% Restart flow input file
SOLUTION_FLOW_FILENAME= solution_flow.dat
%
% Output file format (PARAVIEW, TECPLOT)
OUTPUT_FORMAT= TECPLOT
%
% Output file convergence history (w/o extension)
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 surface flow coefficient (w/o extension)
SURFACE_FLOW_FILENAME= surface_flow
%
% Writing solution file frequency
WRT_SOL_FREQ= 100
%
% Writing convergence history frequency
WRT_CON_FREQ= 1

Any help would be appreciated. Thank you.

whizkid November 19, 2017 23:23

Did you check your y+ values on the airfoil? also, another possibility is that your grid may be bad, such that the neigbour element sizes may not match appropriately.

My recommendation is, try to create an o-grid with first layer height is set to 3e-6 units away from the airfoil. Also, I would use B-C transition model if the freestream turbulence intensity is low.

talbring November 20, 2017 11:53

1 Attachment(s)
I just had a look at the mesh you provided. It seems like that it is slightly corrupted ... That should explain why it is diverging :)


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