[Zen]

I am running simulations at low Mach numbers for a flat plate.
I have created two grids, one with ca.200000 points and another with ca. 13000 points and my y+<=1.
If I run the simulation with the coarse grid the solution converges and gives nice results.
However, if I run it with the fine grid and keep the same parameters i get "nan" values for CL and CD in the history.plt file.

I can't figure out why. Any help is appreciated.

P.S. The same happens if I run the simulation on a coarse grid but at a M=0.1 instead of M=0.15.

Attached is the configuration file I've used and the history.plt file with nan values

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% %
% SU2 configuration file %
% Case description: Turbulent flow over flat plate with zero pressure gradient %
% Author: Thomas D. Economon %
% Institution: Stanford University %
% Date: 2011.11.10 %
% File Version 3.2.2 "eagle" %
% %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% ------------- DIRECT, ADJOINT, AND LINEARIZED PROBLEM DEFINITION ------------%
%
% Physical governing equations (EULER, NAVIER_STOKES,
% TNE2_EULER, TNE2_NAVIER_STOKES,
% WAVE_EQUATION, HEAT_EQUATION, LINEAR_ELASTICITY,
% POISSON_EQUATION)
PHYSICAL_PROBLEM= NAVIER_STOKES
%
% If Navier-Stokes, kind of turbulent model (NONE, SA)
KIND_TURB_MODEL= SST
%
% Mathematical problem (DIRECT, ADJOINT, LINEARIZED, ONE_SHOT_ADJOINT)
MATH_PROBLEM= DIRECT
%
% Restart solution (NO, YES)
RESTART_SOL= NO
% ----------- COMPRESSIBLE AND INCOMPRESSIBLE FREE-STREAM DEFINITION ----------%
%
% Mach number (non-dimensional, based on the free-stream values)
MACH_NUMBER= 0.15
%
% Angle of attack (degrees)
AoA= 0.0
%
% Side-slip angle (degrees)
SIDESLIP_ANGLE= 0.0
%
% Free-stream temperature (288.15 K by default)
FREESTREAM_TEMPERATURE= 288.15
%
% Reynolds number (non-dimensional, based on the free-stream values)
REYNOLDS_NUMBER= 7.68E5
%
% Reynolds length (in meters)
REYNOLDS_LENGTH= 0.34
% ---------------------- 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_MOMENT= 1.0
%
% Reference area for force coefficients (0 implies automatic calculation)
REF_AREA= 0
%
% Reference pressure (101325.0 N/m^2 by default)
REF_PRESSURE= 1.0
%
% Reference temperature (273.15 K by default)
REF_TEMPERATURE= 1.0
%
% Reference density (1.2886 Kg/m^3 (air), 998.2 Kg/m^3 (water))
REF_DENSITY= 1.0
%
% -------------------- BOUNDARY CONDITION DEFINITION --------------------------%
%
% Navier-Stokes wall boundary marker(s) (NONE = no marker)
MARKER_HEATFLUX= ( wall, 0.0 )
%
MARKER_FAR= (inlet, outlet, farfield)
%
% Inlet boundary marker(s) (NONE = no marker)
% Format: ( inlet marker, total temperature, total pressure, flow_direction_x,
% flow_direction_y, flow_direction_z, ... )
%MARKER_INLET= ( inlet, 302.4, 118309.784, 1.0, 0.0, 0.0 )
%
% Outlet boundary marker(s) (NONE = no marker)
% Format: ( outlet marker, back pressure, ... )
%MARKER_OUTLET= ( outlet, 115056.0, farfield, 115056.0 )
%
% Symmetry boundary marker(s) (NONE = no marker)
MARKER_SYM= ( symmetry )
%
% Marker(s) of the surface to be plotted or designed
MARKER_PLOTTING= ( wall )
%
% Marker(s) of the surface where the functional (Cd, Cl, etc.) will be evaluated
MARKER_MONITORING= ( wall )
% ------------- COMMON PARAMETERS DEFINING THE NUMERICAL METHOD ---------------%
%
% Numerical method for spatial gradients (GREEN_GAUSS, LEAST_SQUARES,
% WEIGHTED_LEAST_SQUARES)
NUM_METHOD_GRAD= GREEN_GAUSS
%
% Courant-Friedrichs-Lewy condition of the finest grid
CFL_NUMBER= 10.0
%
% CFL ramp (factor, number of iterations, CFL limit)
CFL_RAMP= ( 1.2, 250, 1.0 )
%
% Runge-Kutta alpha coefficients
RK_ALPHA_COEFF= ( 0.66667, 0.66667, 1.000000 )
%
% Number of total iterations
EXT_ITER= 99999
% ----------------------- SLOPE LIMITER DEFINITION ----------------------------%
%
% Reference element length for computing the slope and sharp edges limiters.
REF_ELEM_LENGTH= 0.1
%
% Coefficient for the limiter
LIMITER_COEFF= 1.0
%
% Coefficient for the sharp edges limiter
SHARP_EDGES_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= NO
% -------------------------- MULTIGRID PARAMETERS -----------------------------%
%
% Multi-Grid Levels (0 = no multi-grid)
MGLEVEL= 3
%
% Multi-Grid Cycle (0 = V cycle, 1 = W Cycle)
MGCYCLE= 0
%
% Maximum number of children in the agglomeration stage
MAX_CHILDREN= 250
%
% Maximum length of an agglomerated element (relative to the domain)
MAX_DIMENSION= 0.1
%
% Multigrid pre-smoothing level
MG_PRE_SMOOTH= ( 1, 2, 3, 3 )
%
% Multigrid post-smoothing level
MG_POST_SMOOTH= ( 2, 2, 2, 2)
%
% Jacobi implicit smoothing of the correction
MG_CORRECTION_SMOOTH= ( 0, 0, 0, 0 )
%
% Damping factor for the residual restriction
MG_DAMP_RESTRICTION= 0.8
%
% Damping factor for the correction prolongation
MG_DAMP_PROLONGATION= 0.8
% -------------------- 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
% -------------------- 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
%
% Slope limiter (VENKATAKRISHNAN, MINMOD)
SLOPE_LIMITER_TURB= VENKATAKRISHNAN
%
% Time discretization (EULER_IMPLICIT)
TIME_DISCRE_TURB= EULER_IMPLICIT
% --------------------------- PARTITIONING STRATEGY ---------------------------%
% Write a paraview file for each partition (NO, YES)
VISUALIZE_PART= NO
% --------------------------- CONVERGENCE PARAMETERS --------------------------%
%
% Convergence criteria (CAUCHY, RESIDUAL)
CONV_CRITERIA= RESIDUAL
%
% Residual reduction (order of magnitude with respect to the initial value)
RESIDUAL_REDUCTION= 4
%
% Min value of the residual (log10 of the residual)
RESIDUAL_MINVAL= -15
%
% 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
%
% Epsilon for full multigrid method evaluation
FULLMG_CAUCHY_EPS= 1E-4
% ------------------------- INPUT/OUTPUT INFORMATION --------------------------%
(...)

TITLE = "SU2 Simulation"
VARIABLES = "Iteration","CLift","CDrag","CSideForce","CMx","CMy","CMz","CFx","CFy","CFz","CL/CD","Res_Flow[0]","Res_Flow[1]","Res_Flow[2]","Res_Flow[3]","Res_Flow[4]","Res_Turb[0]","Res_Turb[1]","Linear_Solver_Iterations","Time(min)"
ZONE T= "Convergence history"
           0,         -nan,         -nan, 0.0000000000, 0.0000000000, 0.0000000000,         -nan,         -nan,         -nan, 0.0000000000,         -nan, -15.9846856557, -13.9265125380, -13.8233443039, -10.5124533135, 0.0000000000, 0.0419222738, 3.6516429409, 4.0000000000, 0.0299452980
           1,         -nan,         -nan, 0.0000000000, 0.0000000000, 0.0000000000,         -nan,         -nan,         -nan, 0.0000000000,         -nan, -3.6954519447, -1.5442531325, -1.1882649389, 1.7752025304, 0.0000000000, -0.0353532016, 5.3434581364, 3.0000000000, 0.0546764652
           2,         -nan,         -nan, 0.0000000000, 0.0000000000, 0.0000000000,         -nan,         -nan,         -nan, 0.0000000000,         -nan, -3.8676843444, -1.4815741116, -1.3597587230, 1.6052160896, 0.0000000000, -0.1042338798, 5.3375754735, 3.0000000000, 0.0822579821
           3,         -nan,         -nan, 0.0000000000, 0.0000000000, 0.0000000000,         -nan,         -nan,         -nan, 0.0000000000,         -nan, -3.8855504594, -1.4444749862, -1.6164142866, 1.5843708437, 0.0000000000, -0.1662656983, 5.3116471667, 3.0000000000, 0.1137784481
           4,         -nan,         -nan, 0.0000000000, 0.0000000000, 0.0000000000,         -nan,         -nan,         -nan, 0.0000000000,         -nan, -3.9637091757, -1.4399159288, -1.8265368904, 1.5041123760, 0.0000000000, -0.2225641911, 5.2699935908, 4.0000000000, 0.1470720649
           5,         -nan,         -nan, 0.0000000000, 0.0000000000, 0.0000000000,         -nan,         -nan,         -nan, 0.0000000000,         -nan, -4.1157328703, -1.4550295523, -1.8058019555, 1.3510765514, 0.0000000000, -0.2739458981, 5.2182425628, 4.0000000000, 0.1804092487
           6,         -nan,         -nan, 0.0000000000, 0.0000000000, 0.0000000000,         -nan,         -nan,         -nan, 0.0000000000,         -nan, -4.2963276198, -1.4767874066, -1.8192751668, 1.1691403734, 0.0000000000, -0.3211715772, 5.1625753899, 4.0000000000, 0.2137426297
(...)

[Zen]

The problem was with REF_AREA erroneously set to 0 for a 2D case.