[jw-89]

Dear SU2 Users,

below I have attached a full configuration of the problem I am trying to solve with SU2. At the moment only the Lax-Friedrich scheme converges, which is good but I have to be careful with artificial dissipation. A better choice here would be rather the FDS method. Unfortunately, the SU2 solver does not converge with this setting. Just for your knowledge, Fluent is able to solve this problem with the second-order upwind.

I believe that the reason for instability is a special form of my boundary condition. Velocity inlet is put not on the whole face but only on an internal surface. The remaining part is treated as a wall. I have also analyzed cases where the whole face is marked as velocity inlet. No instability occurs in these situations and all available schemes converge.

How can I stabilize the upwind scheme in this particular setting? I would be grateful for your help.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% SU2 Configuration File %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% ---------------------- FLUID FLOW AND TURBULENCE MODEL ----------------------%
%
% Physical governing equations (INC_NAVIER_STOKES, INS_RANS)
SOLVER= INC_RANS
%
% Solve the energy equation in the incompressible flow solver
INC_ENERGY_EQUATION = YES
%
% If Navier-Stokes, kind of turbulent model (NONE, SST)
KIND_TURB_MODEL= SST
%
FLUID_MODEL= INC_IDEAL_GAS
%
% Viscosity model (CONSTANT_VISCOSITY).
VISCOSITY_MODEL= CONSTANT_VISCOSITY
%
% Molecular Viscosity that would be constant
MU_CONSTANT= 1.716E-5
%
% Non-dimensionalization scheme for incompressible flows. Options are
INC_NONDIM= DIMENSIONAL
%
% ----------- INCOMPRESSIBLE FLOW INITIAL AND BOUNDARY CONDITIONS -------------%
%
% Initial density for incompressible flows (1.2886 kg/m^3 by default)
INC_DENSITY_INIT= 1.2
%
% Initial velocity for incompressible flows (1.0,0,0 m/s by default)
INC_VELOCITY_INIT= (0, 0, -1)
%
% Initial fluid temperature
INC_TEMPERATURE_INIT= 293.15
%
% List of inlet types for incompressible flows. List length must
% match number of inlet markers. Options: VELOCITY_INLET, PRESSURE_INLET.
INC_INLET_TYPE= VELOCITY_INLET
%
% List of outlet types for incompressible flows. List length must
% match number of outlet markers. Options: PRESSURE_OUTLET, MASS_FLOW_OUTLET.
INC_OUTLET_TYPE= PRESSURE_OUTLET
%
% Euler wall (Slip) boundary marker(s) (NONE = no marker)
MARKER_EULER= (WALL)
%
% Inc. Velocity: (inlet marker, temperature, velocity magnitude, flow_direction_x,
% flow_direction_y, flow_direction_z, ... ) where flow_direction is
% a unit vector.
MARKER_INLET= (INLET_AIR, 293.15, 1, 0, 0, -1)
%
% Outlet boundary marker(s) (NONE = no marker)
MARKER_OUTLET= (PRESSURE_OUTLET, 0)
%
% -------------------- FLOW NUMERICAL METHOD DEFINITION -----------------------%
%
% Convective numerical method (JST, FDS, LAX-FRIEDRICH)
CONV_NUM_METHOD_FLOW= LAX-FRIEDRICH
MUSCL_FLOW= YES
%
% Convective numerical method (SCALAR_UPWIND).
CONV_NUM_METHOD_TURB= SCALAR_UPWIND
%
% --------------------------- CONVERGENCE PARAMETERS --------------------------%
%
% Number of total iterations
ITER= 10000
%
% Start Cauchy criteria at iteration number.
CONV_STARTITER= 100
%
% Min value of the residual (log10 of the residual).
CONV_RESIDUAL_MINVAL= -4
%
CONV_FIELD= RMS_TEMPERATURE
%
% ------------------------- INPUT/OUTPUT INFORMATION --------------------------%
%
% Mesh input file format (CGNS)
MESH_FORMAT= CGNS
%
% Mesh input file
MESH_FILENAME= mesh_20x20x60_cells_inlet_subface.cgns
%
% Files to output
% Possible formats : (TECPLOT, PARAVIEW_ASCII).
OUTPUT_FILES= (PARAVIEW_ASCII, RESTART)
%
% Output file flow (w/o extension) variables.
VOLUME_FILENAME= flow
%
% Volume output fields/groups
VOLUME_OUTPUT= (COORDINATES, SOLUTION, PRIMITIVE, FIBER)
%
% Screen output fields
%
SCREEN_OUTPUT= (INNER_ITER, RMS_PRESSURE, RMS_VELOCITY-X, RMS_VELOCITY-Y, RMS_VELOCITY-Z, RMS_TEMPERATURE)
%

[raviramesh10]

Originally Posted by jw-89

Dear SU2 Users,

below I have attached a full configuration of the problem I am trying to solve with SU2. At the moment only the Lax-Friedrich scheme converges, which is good but I have to be careful with artificial dissipation. A better choice here would be rather the FDS method. Unfortunately, the SU2 solver does not converge with this setting. Just for your knowledge, Fluent is able to solve this problem with the second-order upwind.

I believe that the reason for instability is a special form of my boundary condition. Velocity inlet is put not on the whole face but only on an internal surface. The remaining part is treated as a wall. I have also analyzed cases where the whole face is marked as velocity inlet. No instability occurs in these situations and all available schemes converge.

How can I stabilize the upwind scheme in this particular setting? I would be grateful for your help.

Hi jw-89,

Did you try to use the JST approach, and also the other second-order schemes available in SU2? Also, could you be more specific about the flow problem that you are trying to solve? That would allow to select specific numerical schemes that would help this purpose.

Cheers

[jw-89]

Hi raviramesh10,

thank you for your replay.

Did you try to use the JST approach, and also the other second-order schemes available in SU2?

Yes, I did try JST but similarly as FDS it diverges. As far as I know, FDS, JST and LAX_FRIEDRICH are the only numerical schemes available for incompressible flow simulations.

Also, could you be more specific about the flow problem that you are trying to solve? That would allow to select specific numerical schemes that would help this purpose.

I thought that the attached configuration file describes best the problem I want to solve. This is an air flow simulation in a chamber shown on the attached picture. In reality the velocity inlet boundary condition should be replaced by a porous medium but it is not available in SU2 (please, correct me if I am wrong). In my problem, there is also a custom momentum and energy source inside the geometry but in order to avoid additional difficulties I wanted to start with this simple problem. As you can see in the configuration, the inlet velocity is very small what makes the incompressibility assumption reasonable.

Do you think that skipping the incompressibility assumption and being then allowed to use other numerical schemes could help? Which scheme do you recommend?

Am I right that in SU2 the flow and energy equations are solved simultaneously? Is it possible to use some coupling scheme?

Thank you for your help.

[hareshram.n]

Hey OP were you able to solve the issue? I have a similar problem solving INC_RANS with SST turbulence model. Only the Lax-Friedrich method converges for my problem.

Thanks