CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > SU2

Divergence issues

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 27, 2020, 06:05
Default Divergence issues
  #1
New Member
 
William Haigh
Join Date: Aug 2020
Posts: 20
Rep Power: 4
WilliamH is on a distinguished road
Hi all,
I am new to SU2 and I am attempting to find a CFD solution including oblique shocks in a scramjet inlet. I created a mesh using Gmsh which I can't attach here. I have also written a configuration file.
However, when I try to run it, it tells me that SU2 has diverged.
If someone could take a look at my mesh and configuration files and tell me what errors there are. Again, I am very new to this so there could be many!

I added a picture of the inlet scramjet for a better understanding.

here is the script of my conf file:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% %
% SU2 configuration file %
% Case description: Scramjet inlet (M1 = 5.1) %
% Author: William Haigh %
% %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% ------------- 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)
SOLVER = EULER

% Specify turbulent model (NONE, SA, SA_NEG, SST)
KIND_TURB_MODEL = NONE

% Mathematical problem (DIRECT, ADJOINT, LINEARIZED)
MATH_PROBLEM = DIRECT

% Restart solution (NO, YES)
RESTART_SOL = NO


% -------------------- COMPRESSIBLE FARFIELD DEFINITION --------------------%

% Mach number (non-dimensional, based on the free-stream values)
MACH_NUMBER = 5.1

% Angle of attack (degrees, only for compressible flows)
AoA = 0.0

% Init option to choose between Reynolds (default) or thermodynamics quantities
% for initializing the solution (REYNOLDS, TD_CONDITIONS)
INIT_OPTION = TD_CONDITIONS

% Free-stream option to choose between density and temperature (default) for
% initializing the solution (TEMPERATURE_FS, DENSITY_FS)
FREESTREAM_OPTION = TEMPERATURE_FS

% Free-stream pressure (101325.0 N/m^2, 2116.216 psf by default)
FREESTREAM_PRESSURE = 4488.0

% Free-stream temperature (288.15 K, 518.67 R by default)
FREESTREAM_TEMPERATURE = 217.92

% Reynolds length (1 m by default)
REYNOLDS_LENGTH = 1.0

% ---------------------- 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= 1.0
%
% Reference area for force coefficients (0 implies automatic calculation)
REF_AREA= 1.0

% ------------------------- IDEAL GAS PROPERTIES -----------------------------%

% Different gas model (STANDARD_AIR, IDEAL_GAS, VW_GAS, PR_GAS)
FLUID_MODEL = IDEAL_GAS

% Ratio of specific heats (1.4 default and the value is hardcoded for the model STANDARD_AIR)
GAMMA_VALUE = 1.4

% Specific gas constant (287.058 J/kg*K default, hardcoded for model STANDARD_AIR)
GAS_CONSTANT = 287

% -------------------- BOUNDARY CONDITION DEFINITION --------------------------%

% Euler wall boundary marker(s) (NONE = no marker)
MARKER_EULER = ( Wall )

% Supersonic inlet boundary marker(s) (NONE = no marker)
% Format: (inlet marker, temperature, static pressure, velocity_x,
% velocity_y, velocity_z, ...) i.e. primitive variables specified
MARKER_SUPERSONIC_INLET = ( Inlet, 217.92, 4488, 1509.119697, 0.0, 0.0)

% Supersonic outlet boundary marker(s) (NONE = no marker)
MARKER_SUPERSONIC_OUTLET = ( Outlet )

% ------------------------ SURFACES IDENTIFICATION ----------------------------%

% 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= WEIGHTED_LEAST_SQUARES
%
% Courant-Friedrichs-Lewy condition of the finest grid
CFL_NUMBER= 2
%
% 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= ( 0.1, 2.0, 1, 1e10 )
%
% Runge-Kutta alpha coefficients
RK_ALPHA_COEFF= ( 0.66667, 0.66667, 1.000000 )
%
% Number of total iterations
ITER= 5000
%
% 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 = 0

% Multi-grid cycle (V_CYCLE, W_CYCLE, FULLMG_CYCLE)
MGCYCLE = W_CYCLE

% Multi-grid pre-smoothing level
MG_PRE_SMOOTH = ( 1, 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 = 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= HLLC
%
% 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= 0.006
%
% 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= RUNGE-KUTTA_EXPLICIT

% --------------------------- CONVERGENCE PARAMETERS --------------------------%
%
% Convergence criteria (CAUCHY, RESIDUAL)
CONV_FIELD= RMS_DENSITY
%
% Min value of the residual (log10 of the residual)
CONV_RESIDUAL_MINVAL= -13
%
% 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

% ------------------------- INPUT/OUTPUT INFORMATION --------------------------%

% Mesh input file
MESH_FILENAME = triangless.su2

%Mesh input file format (SU2, CGNS, NETCDF_ASCII)
MESH_FORMAT = SU2

% Mesh output file
MESH_OUT_FILENAME = my_mesh_out.su2

% Restart flow input file
SOLUTION_FILENAME = restart.dat

% Output file format (PARAVIEW, TECPLOT, STL)
OUTPUT_FILES = PARAVIEW_ASCII

% Output file convergence history (w/o extension)
CONV_FILENAME = history

% Output file restart flow
RESTART_FILENAME = restart.dat

% Output file flow (w/o extension) variables
VOLUME_FILENAME = Flow_OS

% Output file surface flow coefficient (w/o extension)
SURFACE_FILENAME = surface

% Writing solution file frequency
WRT_SOL_FREQ = 100

% Writing convergence history frequency
WRT_CON_FREQ = 1
Attached Images
File Type: png X-51.PNG (119.9 KB, 22 views)
WilliamH is offline   Reply With Quote

Old   August 28, 2020, 03:56
Default
  #2
pcg
Senior Member
 
Pedro Gomes
Join Date: Dec 2017
Posts: 419
Rep Power: 11
pcg is on a distinguished road
Use EULER_IMPLICIT instead of RK explicit.
Use the VENKATAKRISHNAN_WANG limiter with coeff ~0.05 or the VAN_ALBADA_EDGE.

I don't have much experience with very high speed flows, but you may also try other schemes like AUSM+up or SLAU (if you do set USE_ACCURATE_FLUX_JACOBIANS=YES as it may allow you to run at higher CFL). More info here: https://su2code.github.io/docs_v7/Convective-Schemes/

For a well posed problem with upwind schemes, 20 linear solver iterations is wasteful, 5-10 should be all you need, or linear solver tolerance 0.05 to 0.01.
pcg is offline   Reply With Quote

Old   August 28, 2020, 11:39
Default
  #3
New Member
 
William Haigh
Join Date: Aug 2020
Posts: 20
Rep Power: 4
WilliamH is on a distinguished road
Thank you for your tips I have tried to apply them but I was still having some errors.
Do you think I could send you the mesh I am using to take a look at it?
I suspect that this might be the problem.
Thanks!
WilliamH is offline   Reply With Quote

Old   August 28, 2020, 19:15
Default
  #4
pcg
Senior Member
 
Pedro Gomes
Join Date: Dec 2017
Posts: 419
Rep Power: 11
pcg is on a distinguished road
SU2 prints some mesh statistics and sanity checks, if you post the screen output for your case I can help you decode that information.
pcg is offline   Reply With Quote

Old   August 29, 2020, 13:55
Default
  #5
New Member
 
William Haigh
Join Date: Aug 2020
Posts: 20
Rep Power: 4
WilliamH is on a distinguished road
This is what I obtain:
------------------- Geometry Preprocessing ( Zone 0 ) -------------------
Two dimensional problem.
14951 grid points.
14625 volume elements.
3 surface markers.
100 boundary elements in index 0 (Marker = inlet).
25 boundary elements in index 1 (Marker = outlet).
525 boundary elements in index 2 (Marker = wall).
14625 quadrilaterals.
Setting point connectivity.
Renumbering points (Reverse Cuthill McKee Ordering).
Recomputing point connectivity.
Setting element connectivity.
Checking the numerical grid orientation.
There has been a re-orientation of 12500 QUADRILATERAL volume elements.
There has been a re-orientation of 650 LINE surface elements.
Identifying edges and vertices.
Computing centers of gravity.
Setting the control volume structure.
Area of the computational grid: 0.97909.
Searching for the closest normal neighbors to the surfaces.
Storing a mapping from global to local point index.
Compute the surface curvature.
Max K: 269.383. Mean K: 2.87427. Standard deviation K: 22.7089.
Checking for periodicity.
Computing mesh quality statistics for the dual control volumes.
+--------------------------------------------------------------+
| Mesh Quality Metric| Minimum| Maximum|
+--------------------------------------------------------------+
| Orthogonality Angle (deg.)| 45.0981| 90|
| CV Face Area Aspect Ratio| 1.11916| 9.17412|
| CV Sub-Volume Ratio| 1| 6.09331|
+--------------------------------------------------------------+
WilliamH is offline   Reply With Quote

Old   August 30, 2020, 11:47
Default
  #6
pcg
Senior Member
 
Pedro Gomes
Join Date: Dec 2017
Posts: 419
Rep Power: 11
pcg is on a distinguished road
Statistics look ok, it should not be a mesh problem.
pcg is offline   Reply With Quote

Old   August 31, 2020, 05:48
Default
  #7
New Member
 
William Haigh
Join Date: Aug 2020
Posts: 20
Rep Power: 4
WilliamH is on a distinguished road
Thanks for all of your help!
WilliamH is offline   Reply With Quote

Reply

Tags
mesh, oblique shock, supersonic flow

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
PEMFC model with FLUENT brahimchoice FLUENT 22 April 19, 2020 16:44
[ANSYS Meshing] Help with element size sandri_92 ANSYS Meshing & Geometry 14 November 14, 2018 08:54
Two Phase Flow In Vertical Pipe stonepreston FLUENT 2 October 31, 2017 09:35
fluent divergence for no reason sufjanst FLUENT 2 March 23, 2016 17:08
Divergence problem Smaras FLUENT 13 February 21, 2013 06:03


All times are GMT -4. The time now is 13:16.