[sangeet]

Hello,
I am currently running a static FSI case of supersonic flow over a compression ramp where the ramp is flexible (FEM grid with clamped-clamped boundary condition). The fluid only case (rigid ramp) converges well but when i try to run the coupled simulation, the structure's convergence is very poor. I tried both large and small deformations in the structural config file and I also tried plane stress and plain strain conditions. None of these cases showed any improvement.

The google drive link with config files and the grid files is

https://drive.google.com/drive/folde...7L?usp=sharing
I have also attached a picture of the grids for a quick idea.

Please kindly suggest on what I could be possibly doing wrong.




The fluid config file is

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                              %
% SU2 configuration file                                                       %
% Case description: Supersonic flow over a wedge in a channel.                 %
% Author: Thomas D. Economon                                                   %
% Institution: Stanford University                                             %
% Date: 2012.10.07                                                             %
% 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)
SOLVER= RANS
%
% If Navier-Stokes, kind of turbulent model (NONE, SA)
KIND_TURB_MODEL= SST
%
% Mathematical problem (DIRECT, CONTINUOUS_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= 2.9
%
% 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= 109.619686800895
%
% Reynolds number (non-dimensional, based on the free-stream values)
REYNOLDS_NUMBER= 148000
%
% Reynolds length (in meters)
REYNOLDS_LENGTH= 4.0454e-03
% ---------------------- REFERENCE VALUE DEFINITION ---------------------------%
%
% Reference origin for moment computation
REF_ORIGIN_MOMENT_X = 0.0
REF_ORIGIN_MOMENT_Y = 0.00
REF_ORIGIN_MOMENT_Z = 0.00
%
% Reference length for pitching, rolling, and yawing non-dimensional moment
REF_LENGTH= 1.0
%
% Reference area for force coefficients (0 implies automatic calculation)
REF_AREA= 1.0

% -------------------- BOUNDARY CONDITION DEFINITION --------------------------%
%
% Navier-Stokes wall boundary marker(s) (NONE = no marker)
MARKER_HEATFLUX= ( WALL1, 0.0, RAMP, 0.0, WALL2, 0.0 )
%
% Supersonic inlet boundary marker(s) (NONE = no marker) 
% Total Conditions: (inlet marker, temperature, static pressure, velocity_x, 
%           velocity_y, velocity_z, ... ), i.e. all variables specified.
MARKER_SUPERSONIC_INLET= ( INLET, 109.619686800895, 13366.4283315982, 608.621433419003, 0.0, 0.0 )
%
% Outlet boundary marker(s) (NONE = no marker)
% Format: ( outlet marker, back pressure (static), ... )
MARKER_OUTLET= ( OUTLET, 10000, UPPER, 10000)

MARKER_SYM= ( SYM_PLANE )
%
% Marker(s) of the surface to be plotted or designed
MARKER_PLOTTING= ( WALL1, RAMP, WALL2 )
%
% Marker(s) of the surface where the functional (Cd, Cl, etc.) will be evaluated
MARKER_MONITORING= ( WALL1, RAMP, WALL2 )

% ------------- COMMON PARAMETERS DEFINING THE NUMERICAL METHOD ---------------%
%
% Numerical method for spatial gradients (GREEN_GAUSS, LEAST_SQUARES, 
%                                         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= NO
%
% Parameters of the adaptive CFL number (factor down, factor up, CFL min value,
%                                        CFL max value )
CFL_ADAPT_PARAM= ( 0.5, 1.5, 0.01, 1000 )
%
% Runge-Kutta alpha coefficients
RK_ALPHA_COEFF= ( 0.66667, 0.66667, 1.000000 )
%
% Number of total iterations
INNER_ITER= 100000
%
% Linear solver for the implicit formulation (BCGSTAB, FGMRES)
LINEAR_SOLVER= FGMRES
%
% Preconditioner of the Krylov linear solver (ILU, JACOBI, LINELET, LU_SGS)
LINEAR_SOLVER_PREC= ILU
%
% 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= 20

% -------------------------- MULTIGRID PARAMETERS -----------------------------%
%
% Multi-Grid Levels (0 = no multi-grid)
MGLEVEL= 4
%
% Multi-grid cycle (V_CYCLE, W_CYCLE, FULLMG_CYCLE)
MGCYCLE= W_CYCLE
%
% Multi-grid pre-smoothing level
MG_PRE_SMOOTH= ( 1, 1, 1, 1 )
%
% 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= 0.5
%
% Damping factor for the correction prolongation
MG_DAMP_PROLONGATION= 0.5    

% -------------------- 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,
%                BARTH_JESPERSEN, VAN_ALBADA_EDGE)
SLOPE_LIMITER_FLOW= NONE
%
% Coefficient for the limiter (smooth regions)
VENKAT_LIMITER_COEFF= 0.02
%
% 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

% -------------------- TURBULENT NUMERICAL METHOD DEFINITION ------------------%
%
% Convective numerical method (SCALAR_UPWIND)
CONV_NUM_METHOD_TURB= SCALAR_UPWIND
%
% Monotonic Upwind Scheme for Conservation Laws (TVD) in the turbulence equations.
%           Required for 2nd order upwind schemes (NO, YES)
MUSCL_TURB= NO
%
% Slope limiter (VENKATAKRISHNAN, MINMOD)
SLOPE_LIMITER_TURB= VENKATAKRISHNAN
%
% Time discretization (EULER_IMPLICIT)
TIME_DISCRE_TURB= EULER_IMPLICIT

%%%%%%%%%%%%%%%%%%%%%%%
% COUPLING CONDITIONS
%%%%%%%%%%%%%%%%%%%%%%%

MARKER_FLUID_LOAD = ( RAMP )

DEFORM_MESH = YES
MARKER_DEFORM_MESH = ( RAMP )

DEFORM_STIFFNESS_TYPE = WALL_DISTANCE
DEFORM_LINEAR_SOLVER = CONJUGATE_GRADIENT
DEFORM_LINEAR_SOLVER_PREC = ILU
DEFORM_LINEAR_SOLVER_ERROR = 1E-10
DEFORM_LINEAR_SOLVER_ITER = 1000
DEFORM_CONSOLE_OUTPUT = NO

% --------------------------- CONVERGENCE PARAMETERS --------------------------%
%
% Convergence criteria (CAUCHY, RESIDUAL)
CONV_FIELD= RMS_DENSITY
%
% Min value of the residual (log10 of the residual)
CONV_RESIDUAL_MINVAL= -10
%
% Start convergence criteria at iteration number
CONV_STARTITER= 10
%
% Number of elements to apply the criteria
CONV_CAUCHY_ELEMS= 100
%
% Epsilon to control the series convergence
CONV_CAUCHY_EPS= 1E-10

%--------------------------- HISTORY ------------------------------------------%
% History output groups (use 'SU2_CFD -d <config_file>' to view list of available fields)
HISTORY_OUTPUT= (ITER, RMS_RES, AERO_COEFF)

% ------------------------- INPUT/OUTPUT INFORMATION --------------------------%
%
% Mesh input file
MESH_FILENAME= Ramp25_Fine_0_5.cgns
%
% Mesh input file format (SU2, CGNS, NETCDF_ASCII)
MESH_FORMAT= CGNS
%
% Writing solution file frequency
OUTPUT_WRT_FREQ= 250
%
% Screen writing frequency
SCREEN_WRT_FREQ_INNER= 10

The structural config file is

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% SU2 configuration file                                                       %
% Case description: FSI: Vertical Cantilever in Channel - Structure            %
% Author: Ruben Sanchez Fernandez                                              %
% Institution: TU Kaiserslautern                                               %
% Date: 2020-02-05                                                             %
% File Version 7.0.2 "Blackbird"                                               %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%
% SOLVER TYPE
%%%%%%%%%%%%%%%%%%%%%%%   
          
SOLVER = ELASTICITY

%%%%%%%%%%%%%%%%%%%%%%%
% STRUCTURAL PROPERTIES
%%%%%%%%%%%%%%%%%%%%%%%

GEOMETRIC_CONDITIONS = LARGE_DEFORMATIONS
MATERIAL_MODEL = NEO_HOOKEAN

ELASTICITY_MODULUS = 1.13E11
POISSON_RATIO = 0.37

FORMULATION_ELASTICITY_2D = PLANE_STRESS

%%%%%%%%%%%%%%%%%%%%%%%
% INPUT
%%%%%%%%%%%%%%%%%%%%%%%

MESH_FORMAT = SU2
MESH_FILENAME = ramp_slender_0_001.su2

%%%%%%%%%%%%%%%%%%%%%%%
% BOUNDARY CONDITIONS
%%%%%%%%%%%%%%%%%%%%%%%

MARKER_CLAMPED = ( LEFT_EDGE, RIGHT_EDGE )
MARKER_PRESSURE = ( LOWER_EDGE, 0)

%%%%%%%%%%%%%%%%%%%%%%%
% COUPLING CONDITIONS
%%%%%%%%%%%%%%%%%%%%%%%

MARKER_FLUID_LOAD = ( UPPER_EDGE )

%%%%%%%%%%%%%%%%%%%%%%%
% SOLUTION METHOD
%%%%%%%%%%%%%%%%%%%%%%%

NONLINEAR_FEM_SOLUTION_METHOD = NEWTON_RAPHSON
INNER_ITER = 40

%%%%%%%%%%%%%%%%%%%%%%%
% CONVERGENCE CRITERIA
%%%%%%%%%%%%%%%%%%%%%%%

CONV_FIELD = RMS_UTOL, RMS_RTOL, RMS_ETOL
CONV_RESIDUAL_MINVAL = -10

%%%%%%%%%%%%%%%%%%%%%%%
% LINEAR SOLVER
%%%%%%%%%%%%%%%%%%%%%%%

LINEAR_SOLVER = CONJUGATE_GRADIENT
LINEAR_SOLVER_PREC = ILU
LINEAR_SOLVER_ERROR = 1E-10
LINEAR_SOLVER_ITER = 1000

% Screen writing frequency
SCREEN_WRT_FREQ_INNER = 1

The FSI master config file is

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% SU2 configuration file                                                       %
% Case description: FSI: Vertical Cantilever in Channel                        %
% Author: Ruben Sanchez Fernandez                                              %
% Institution: TU Kaiserslautern                                               %
% Date: 2020-02-05                                                             %
% File Version 7.0.2 "Blackbird"                                               %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%
% SOLVER TYPE
%%%%%%%%%%%%%%%%%%%%%%%

SOLVER = MULTIPHYSICS

%%%%%%%%%%%%%%%%%%%%%%%
% INPUT
%%%%%%%%%%%%%%%%%%%%%%%

MULTIZONE_MESH = NO
CONFIG_LIST = (flowSST.cfg, ramp.cfg)

%%%%%%%%%%%%%%%%%%%%%%%
% SOLUTION STRATEGY
%%%%%%%%%%%%%%%%%%%%%%%

MULTIZONE_SOLVER = BLOCK_GAUSS_SEIDEL
OUTER_ITER = 1000

%%%%%%%%%%%%%%%%%%%%%%%
% CONVERGENCE CRITERIA
%%%%%%%%%%%%%%%%%%%%%%%

CONV_FIELD = AVG_BGS_RES[0], AVG_BGS_RES[1]
CONV_RESIDUAL_MINVAL = -10

%%%%%%%%%%%%%%%%%%%%%%%
% Relaxation
%%%%%%%%%%%%%%%%%%%%%%%
%BGS_RELAXATION= FIXED_PARAMETER
%STAT_RELAX_PARAMETER= 0.8

%%%%%%%%%%%%%%%%%%%%%%%
% COUPLING CONDITIONS
%%%%%%%%%%%%%%%%%%%%%%%

MARKER_ZONE_INTERFACE = (RAMP, UPPER_EDGE)

%%%%%%%%%%%%%%%%%%%%%%%
% OUTPUT
%%%%%%%%%%%%%%%%%%%%%%%

SCREEN_OUTPUT = (OUTER_ITER, AVG_BGS_RES[0], AVG_BGS_RES[1], DEFORM_MIN_VOLUME[0], DEFORM_ITER[0])
WRT_ZONE_CONV = YES

OUTPUT_FILES = (RESTART, PARAVIEW, SURFACE_PARAVIEW, SURFACE_CSV)
SOLUTION_FILENAME = solution_fsi_steady
RESTART_FILENAME = restart_fsi_steady
VOLUME_FILENAME = fsi_steady

HISTORY_OUTPUT = ITER, BGS_RES[0], AERO_COEFF[0], BGS_RES[1]

WRT_ZONE_HIST = YES
CONV_FILENAME= history

[pcg]

Thanks for uploading all files, makes it a lot easier.

A common issue with structural problems in SU2 is that normal iterative linear solvers are not strong enough, the 1000 iterations you have with ILU and conjugate gradient barely drop the residuals.
If you compile the code with PaStiX you can solve anything (there are instruction in TestCases/pastix_support).

The other issue you have is that either the structure is too flexible or there is supposed to be some pressure applied from the other side.
I ran it for one outer iteration and the plate becomes a balloon.

For FSI the pressure load is applied relative to free-stream (P - Pinf) so, as if the "internal" pressure were Pinf. You may need to increase the pressure load on the LOWER_EDGE marker if this is not what you want to simulate.

Here are the configs for how I got it to converge.
EDIT: with a much larger elasticity modulus.

[sangeet]

Thank you for your suggestions. I will try the case with PaStiX.



Also, does it mean that instead of (p-pinf) if I want (p) to be load on the solid-fluid interface, I should specify the pressure load on the LOWER_EDGE as pinf?

[pcg]

For that it should be -pinf because the normal points in the opposite direction.