[CarlosLozano]

Hi,
I'm running a simple transonic, inviscid, steady case on a NACA0012 with M = 0.8 and aoa = 1.25. I'm using the mesh provided in the suite (mesh_NACA0012_inv.su2) and Roe's scheme in both the flow and adjoint solvers and I'm having problems getting them to converge. Quite early on the residuals stall and oscillate, as do the corresponding metrics (Cl, Cd & Sens_Geo, Sens_aoa). It is probably a limiter-related issue (I'm using Venkat.). I copy the settings below. Any clues?

% -------------------------- 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= 1.0
%
% Damping factor for the correction prolongation
MG_DAMP_PROLONGATION= 1.0

% -------------------- 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_LIMITER
%
% Slope limiter (VENKATAKRISHNAN, MINMOD)
SLOPE_LIMITER_FLOW= VENKATAKRISHNAN
%
% Coefficient for the limiter (smooth regions)
LIMITER_COEFF= 0.1
%
% 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
%
% ---------------- ADJOINT-FLOW NUMERICAL METHOD DEFINITION -------------------%
%
% Convective numerical method (JST, LAX-FRIEDRICH, ROE)
CONV_NUM_METHOD_ADJFLOW= ROE
%
% Spatial numerical order integration (1ST_ORDER, 2ND_ORDER, 2ND_ORDER_LIMITER)
%
SPATIAL_ORDER_ADJFLOW= 2ND_ORDER_LIMITER
%
% Slope limiter (VENKATAKRISHNAN, SHARP_EDGES)
SLOPE_LIMITER_ADJFLOW= VENKATAKRISHNAN
%
% 1st, 2nd, and 4th order artificial dissipation coefficients
AD_COEFF_ADJFLOW= ( 0.15, 0.5, 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

[mhd_mrt]

Originally Posted by CarlosLozano

Hi,
I'm running a simple transonic, inviscid, steady case on a NACA0012 with M = 0.8 and aoa = 1.25. I'm using the mesh provided in the suite (mesh_NACA0012_inv.su2) and Roe's scheme in both the flow and adjoint solvers and I'm having problems getting them to converge. Quite early on the residuals stall and oscillate, as do the corresponding metrics (Cl, Cd & Sens_Geo, Sens_aoa). It is probably a limiter-related issue (I'm using Venkat.). I copy the settings below. Any clues?

% -------------------------- 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= 1.0
%
% Damping factor for the correction prolongation
MG_DAMP_PROLONGATION= 1.0

% -------------------- 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_LIMITER
%
% Slope limiter (VENKATAKRISHNAN, MINMOD)
SLOPE_LIMITER_FLOW= VENKATAKRISHNAN
%
% Coefficient for the limiter (smooth regions)
LIMITER_COEFF= 0.1
%
% 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
%
% ---------------- ADJOINT-FLOW NUMERICAL METHOD DEFINITION -------------------%
%
% Convective numerical method (JST, LAX-FRIEDRICH, ROE)
CONV_NUM_METHOD_ADJFLOW= ROE
%
% Spatial numerical order integration (1ST_ORDER, 2ND_ORDER, 2ND_ORDER_LIMITER)
%
SPATIAL_ORDER_ADJFLOW= 2ND_ORDER_LIMITER
%
% Slope limiter (VENKATAKRISHNAN, SHARP_EDGES)
SLOPE_LIMITER_ADJFLOW= VENKATAKRISHNAN
%
% 1st, 2nd, and 4th order artificial dissipation coefficients
AD_COEFF_ADJFLOW= ( 0.15, 0.5, 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

Hi Carlos,

Try lowering the CFL number. Also th elimiter Coeff, try lowering that too. It could also be due to time descritization. I used to get numerical instability due to implicit time scheme. Try using Explicit and lowering the CFL number to see if you get any improvement.

Cheers,

[CarlosLozano]

Originally Posted by mhd_mrt

Hi Carlos,

Try lowering the CFL number. Also th elimiter Coeff, try lowering that too. It could also be due to time descritization. I used to get numerical instability due to implicit time scheme. Try using Explicit and lowering the CFL number to see if you get any improvement.

Cheers,

Thanks for the advice

[fpalacios]

If you eliminate the multigrid the you can really increase the CFL number.
Best,
Francisco

[CarlosLozano]

Originally Posted by fpalacios

If you eliminate the multigrid the you can really increase the CFL number.
Best,
Francisco

Thanks a lot for the advice
Regards