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Discrepancy in Exit Mach Number: Validation with Experimental Nozzle Data

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Old   January 6, 2024, 01:20
Default Discrepancy in Exit Mach Number: Validation with Experimental Nozzle Data
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I am currently working on validating my CFD results using experimental nozzle data. The experimental conditions specify a total pressure of 517100 Pa, total temperature of 843.33 K, and a wall temperature set to 0.5 times the total temperature. Additionally, the exit Mach number is expected to be 2.5.

However, upon running the simulation with the provided boundary conditions, I am getting an exit Mach number of 1.9 instead of the expected 2.5. I have attached my configuration file for your reference.

Quote:
% ------------- DIRECT, ADJOINT, AND LINEARIZED PROBLEM DEFINITION ------------%
%
% Physical governing equations (EULER, NAVIER_STOKES,
% FEM_EULER, FEM_NAVIER_STOKES, FEM_RANS, FEM_LES,
% WAVE_EQUATION, HEAT_EQUATION, FEM_ELASTICITY,
% POISSON_EQUATION)
SOLVER= RANS
%
% Specify turbulence model (NONE, SA, SST)
KIND_TURB_MODEL= SA
SST_OPTIONS= V2003m
%
% Mathematical problem (DIRECT, CONTINUOUS_ADJOINT, DISCRETE_ADJOINT)
MATH_PROBLEM= DIRECT
%
% Restart solution (NO, YES)
RESTART_SOL= NO
%
% System of measurements (SI, US)
% International system of units (SI): ( meters, kilograms, Kelvins,
% Newtons = kg m/s^2, Pascals = N/m^2,
% Density = kg/m^3, Speed = m/s,
% Equiv. Area = m^2 )
% United States customary units (US): ( inches, slug, Rankines, lbf = slug ft/s^2,
% psf = lbf/ft^2, Density = slug/ft^3,
% Speed = ft/s, Equiv. Area = ft^2 )
SYSTEM_MEASUREMENTS= SI
%
% -------------------- COMPRESSIBLE FREE-STREAM DEFINITION --------------------%
%
% Mach number (non-dimensional, based on the free-stream values)
MACH_NUMBER= 1E-9
%
% Angle of attack (degrees, only for compressible flows)
AOA= 0.0
%
% Side-slip angle (degrees, only for compressible flows)
SIDESLIP_ANGLE= 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= 517100
%
% Free-stream temperature (288.15 K, 518.67 R by default)
FREESTREAM_TEMPERATURE= 843.33
%
% Compressible flow non-dimensionalization (DIMENSIONAL, FREESTREAM_PRESS_EQ_ONE,
% FREESTREAM_VEL_EQ_MACH, FREESTREAM_VEL_EQ_ONE)
REF_DIMENSIONALIZATION= DIMENSIONAL

% ---- IDEAL GAS, POLYTROPIC, VAN DER WAALS AND PENG ROBINSON CONSTANTS -------%
%
% Fluid model (STANDARD_AIR, IDEAL_GAS, VW_GAS, PR_GAS,
% CONSTANT_DENSITY, INC_IDEAL_GAS, INC_IDEAL_GAS_POLY)
FLUID_MODEL= STANDARD_AIR
%
% Ratio of specific heats (1.4 default and the value is hardcoded
% for the model STANDARD_AIR, compressible only)
GAMMA_VALUE= 1.345
%
% Specific gas constant (287.058 J/kg*K default and this value is hardcoded
% for the model STANDARD_AIR, compressible only)
GAS_CONSTANT= 287.058

% --------------------------- VISCOSITY MODEL ---------------------------------%
%
% Viscosity model (SUTHERLAND, CONSTANT_VISCOSITY, POLYNOMIAL_VISCOSITY).
VISCOSITY_MODEL= SUTHERLAND
MU_REF= 1.716E-5
% Sutherland Temperature Ref (273.15 K default value for AIR SI)
MU_T_REF= 273.15
%
% Sutherland constant (110.4 default value for AIR SI)
SUTHERLAND_CONSTANT= 110.4
%
% Molecular Viscosity that would be constant (1.716E-5 by default)
MU_CONSTANT= 1.21409E-05

% --------------------------- THERMAL CONDUCTIVITY MODEL ----------------------%
%
% Conductivity model (CONSTANT_CONDUCTIVITY, CONSTANT_PRANDTL).
CONDUCTIVITY_MODEL= CONSTANT_PRANDTL
%
% Molecular Thermal Conductivity that would be constant (0.0257 by default)
THERMAL_CONDUCTIVITY_CONSTANT= 0.0257
%
% Laminar Prandtl number (0.72 (air), only for CONSTANT_PRANDTL)
PRANDTL_LAM= 0.72
%
% Turbulent Prandtl number (0.9 (air), only for CONSTANT_PRANDTL)
PRANDTL_TURB= 0.90

% -------------------- BOUNDARY CONDITION DEFINITION --------------------------%
%
% Navier-Stokes (no-slip), constant heat flux wall marker(s) (NONE = no marker)
% Format: ( marker name, constant heat flux (J/m^2), ... )
MARKER_ISOTHERMAL = (WALL, 421.665)
%MARKER_WALL_FUNCTIONS= ( WALL, STANDARD_WALL_FUNCTION )
%
% Symmetry boundary marker(s) (NONE = no marker)
MARKER_SYM= ( SYMMETRY )
%
% Riemann boundary marker(s) (NONE = no marker)
% Format: (marker, data kind flag, list of data)
MARKER_RIEMANN= ( INFLOW, TOTAL_CONDITIONS_PT, 517100 , 843.33, 1.0, 0.0, 0.0, OUTFLOW, STATIC_PRESSURE, 29861.76, 0.0, 0.0, 0.0, 0.0 )
%INLET_TYPE= TOTAL_CONDITIONS
%MARKER_INLET = (INFLOW, 843.33, 517100, 1.0, 0.0, 0.0)
%MARKER_OUTLET = (OUTFLOW, 29861.76)
% ------------- COMMON PARAMETERS DEFINING THE NUMERICAL METHOD ---------------%
%
% Numerical method for spatial gradients (GREEN_GAUSS, WEIGHTED_LEAST_SQUARES)
NUM_METHOD_GRAD= GREEN_GAUSS
%
% CFL number (initial value for the adaptive CFL number)
CFL_NUMBER= 0.6
%
% 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, 10.0, 1000.0 )
%
% Maximum Delta Time in local time stepping simulations
MAX_DELTA_TIME= 1E6

% ----------- SLOPE LIMITER AND DISSIPATION SENSOR DEFINITION -----------------%
%
% Monotonic Upwind Scheme for Conservation Laws (TVD) in the flow equations.
% Required for 2nd order upwind schemes (NO, YES)
MUSCL_FLOW= NO
%
% Slope limiter (NONE, VENKATAKRISHNAN, VENKATAKRISHNAN_WANG,
% BARTH_JESPERSEN, VAN_ALBADA_EDGE)
SLOPE_LIMITER_FLOW= VENKATAKRISHNAN_WANG
VENKAT_LIMITER_COEFF= 0.01
%
% Monotonic Upwind Scheme for Conservation Laws (TVD) in the turbulence equations.
% Required for 2nd order upwind schemes (NO, YES)
MUSCL_TURB= NO

% ------------------------ LINEAR SOLVER DEFINITION ---------------------------%
%
% Linear solver or smoother for implicit formulations (BCGSTAB, FGMRES, SMOOTHER_JACOBI,
% SMOOTHER_ILU, SMOOTHER_LUSGS,
% SMOOTHER_LINELET)
LINEAR_SOLVER= FGMRES
%
% Preconditioner of the Krylov linear solver (ILU, LU_SGS, LINELET, JACOBI)
LINEAR_SOLVER_PREC= ILU
%
% Linael solver ILU preconditioner fill-in level (0 by default)
LINEAR_SOLVER_ILU_FILL_IN= 0
%
% Minimum error of the linear solver for implicit formulations
LINEAR_SOLVER_ERROR= 1E-6
%
% Max number of iterations of the linear solver for the implicit formulation
LINEAR_SOLVER_ITER= 10

% -------------------------- MULTIGRID PARAMETERS -----------------------------%
%
MGLEVEL= 0
MGCYCLE= V_CYCLE
MG_PRE_SMOOTH= ( 1, 1, 2, 2 )
MG_POST_SMOOTH= ( 0, 0, 0, 0 )
MG_CORRECTION_SMOOTH= ( 0, 0, 0, 0 )
MG_DAMP_RESTRICTION= 0.7
MG_DAMP_PROLONGATION= 0.7

% -------------------- FLOW NUMERICAL METHOD DEFINITION -----------------------%
%
% Convective numerical method (JST, LAX-FRIEDRICH, CUSP, ROE, AUSM, AUSMPLUSUP, AUSMPLUSUP2, HLLC,
% TURKEL_PREC, MSW, FDS)
CONV_NUM_METHOD_FLOW= ROE
%
% Entropy fix coefficient (0.0 implies no entropy fixing, 1.0 implies scalar
% artificial dissipation)
ENTROPY_FIX_COEFF= 0.01
%
% 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
%
% Time discretization (EULER_IMPLICIT)
TIME_DISCRE_TURB= EULER_IMPLICIT
%
% Reduction factor of the CFL coefficient in the turbulence problem
CFL_REDUCTION_TURB= 1.0

% --------------------------- CONVERGENCE PARAMETERS --------------------------%
%
% Number of total iterations
ITER= 1000000
%
% Min value of the residual (log10 of the residual)
CONV_RESIDUAL_MINVAL= -24
%
% Start convergence criteria at iteration number
CONV_STARTITER= 10

% ------------------------- INPUT/OUTPUT INFORMATION --------------------------%
%
% Mesh input file
MESH_FILENAME= Mesh.su2
%
% Mesh input file format (SU2, CGNS)
MESH_FORMAT= SU2
%
% Mesh output file
MESH_OUT_FILENAME= mesh_out.su2
%
% Restart flow input file
SOLUTION_FILENAME= solution_flow.dat
%
% Output file format (TECPLOT, TECPLOT_BINARY, PARAVIEW, PARAVIEW_BINARY,
% FIELDVIEW, FIELDVIEW_BINARY)
TABULAR_FORMAT= CSV
%
% Output file convergence history (w/o extension)
CONV_FILENAME= history
%
% Output file restart flow
RESTART_FILENAME= restart_flow.dat
%
% Output file flow (w/o extension) variables
VOLUME_FILENAME= flow
VOLUME_OUTPUT= (HEAT_FLUX,TEMPERATURE,PRESSURE, MACH NUMBER)
OUTPUT_FILES=(PARAVIEW_MULTIBLOCK,PARAVIEW, TECPLOT)
%
% Output file surface flow coefficient (w/o extension)
SURFACE_FILENAME= surface_flow
%
% Writing solution file frequency
OUTPUT_WRT_FREQ= 1000
%
% Screen output
SCREEN_OUTPUT= (INNER_ITER, RMS_DENSITY, RMS_TKE, RMS_DISSIPATION)
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Old   January 8, 2024, 02:55
Default No reply in 2 days.
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I don't understand why this thread is not addressed yet ?
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Old   January 8, 2024, 04:28
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Dear Sean,
Please understand that the SU2 community is an open source community run by volunteers and the researchers answering questions on cfd-online do that on a voluntary basis.

It might be that your question is difficult to answer, does not contain enough information to give an answer (please see: Guide: How to ask a question on the forums)
or that 2 days is simply not enough time to expect a response, especially considering that it was asked in the weekend.

My rule of thumb is that you can only expect a (high quality) answer if you ask a high quality question. Just giving a config file and saying that it does not give you the expected result is not sufficient.


You might consider adding:
1. which case you are trying to simulate, preferably with a reference to a website or journal paper.
2. A link to the mesh or additional results so the problem can be reproduced by the reader. Note that most people will not take the effort to submit a 500M cell mesh to a cluster just to help answering a problem, so the problem should be small.
3. What you tried yourself to investigate the problem: Converged? Mesh-independent solution? Setup according to literature?


Hope this helps.
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Old   January 8, 2024, 04:45
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Quote:
Originally Posted by bigfootedrockmidget View Post
Dear Sean,
Please understand that the SU2 community is an open source community run by volunteers and the researchers answering questions on cfd-online do that on a voluntary basis.

It might be that your question is difficult to answer, does not contain enough information to give an answer (please see: Guide: How to ask a question on the forums)
or that 2 days is simply not enough time to expect a response, especially considering that it was asked in the weekend.

My rule of thumb is that you can only expect a (high quality) answer if you ask a high quality question. Just giving a config file and saying that it does not give you the expected result is not sufficient.


You might consider adding:
1. which case you are trying to simulate, preferably with a reference to a website or journal paper.
2. A link to the mesh or additional results so the problem can be reproduced by the reader. Note that most people will not take the effort to submit a 500M cell mesh to a cluster just to help answering a problem, so the problem should be small.
3. What you tried yourself to investigate the problem: Converged? Mesh-independent solution? Setup according to literature?


Hope this helps.
Dear bigfoot,

I appreciate your response and the insights you provided regarding the SU2 community on cfd-online. I understand that the community is driven by volunteers, and I want to express my gratitude for the effort put into answering questions.

As a new member seeking insights, I also value the importance of asking high-quality questions to receive meaningful responses. I acknowledge your suggestions on providing additional information, and I will make an effort to improve the clarity and detail of my future queries.

While I understand that it may take time to address complex questions, I was hoping to receive some guidance or suggestions to steer me in the right direction. I am eager to learn and contribute to the community, and any assistance or inquiries related to my initial post would be greatly appreciated.
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Old   January 8, 2024, 06:17
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Maybe you can tell us which case you are simulating [supersonic wedge?].

Maybe you can tell us which data you have found that you are comparing to so we can check the physics setup.
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Old   January 8, 2024, 06:58
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Quote:
Originally Posted by bigfootedrockmidget View Post
Maybe you can tell us which case you are simulating [supersonic wedge?].

Maybe you can tell us which data you have found that you are comparing to so we can check the physics setup.
Thank you for your response, I am validating with Back, L. H., Massier, P. F., and Gier, H. L., “Convective Heat Transfer
in a Convergent–Divergent Nozzle,” International Journal of Heat Mass
Transfer.(CASE 262)

A converging–diverging nozzle with a throat diameter of 0.0458 m and
an exit diameter of 0.1227 m. High-pressure air was heated by the
internal combustion of methanol and flowed along a cooled constant
area duct with a length of 0.4572 m and a diameter of 0.355 m before
entering the nozzle.

The gas could be treated as a calorically perfect
gas with a ratio-of-specific heats γ of 1.345. The nozzle exit Mach
number was approximately 2.5. The molecular viscosity and thermal
conductivity were assumed to vary according to Sutherland’s law.
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Old   January 8, 2024, 07:05
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Quote:
Originally Posted by bigfootedrockmidget View Post
Maybe you can tell us which case you are simulating [supersonic wedge?].

Maybe you can tell us which data you have found that you are comparing to so we can check the physics setup.
And the mesh can be found in the following link
https://drive.google.com/file/d/1CAS...usp=drive_link
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Old   January 8, 2024, 07:34
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Thanks. The link has restricted access, can you open access to everybody?
Can you share figures where you compare your simulations with the measurements?
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Old   January 8, 2024, 08:27
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One thing I noticed is that this is a round nozzle, you can simulate it in 2D with axisymmetry, so you need to set AXISYMMETRY=YES
But you need to then set the turbulence model to SST because we did not implement the axisymmetric terms for SA.
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Old   January 9, 2024, 01:09
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Quote:
Originally Posted by bigfootedrockmidget View Post
One thing I noticed is that this is a round nozzle, you can simulate it in 2D with axisymmetry, so you need to set AXISYMMETRY=YES
But you need to then set the turbulence model to SST because we did not implement the axisymmetric terms for SA.
Dear bigfoot,

Thank you for this suggestion. Earlier I was using axisymmetric condition with SA model but my simulation used to fail. Now following your suggestion, as I could see, I am getting Mach number 2.4 (simulation is still running) , It seems convincing. Earlier I used to get Mach 1.9 only. Once simulation is over and let me compare my results, I will update here.
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Old   January 9, 2024, 02:51
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Sorry for the slight detour on this topic, but I noticed that in the configuration FREESTREAM_TEMPERATURE= 843.33 (K) which is the total_temperature, not the static one.

The SU2 documentation is not strictly univocal as, for example in : SU2 Physical Definition FREESTREAM_TEMPERATURE is referred as static temperature, while in NICFD_nozzle tutorial it is referred as stagnation temperature (and I can tell that this tutorial is somewhat similar to the run @bgulzar22 is carrying out).

I understand that this parameters drive the initialization of the simulation, so at the end, the solution will be driven by the Boundary Conditions, anyways, can anybody please check/clarify on that?

Ok, nevermind, I noticed that the MACH_NUMBER is close to 0 so the configuration is initializing with stagnation conditions the flow ( total pressure and temperature, 0 velocity), and then let expand out ...

Last edited by giovanni.medici; January 9, 2024 at 03:20. Reason: I noticed the MACH_NUMBER in the configuration
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Old   January 9, 2024, 03:33
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Quote:
Originally Posted by giovanni.medici View Post
Sorry for the slight detour on this topic, but I noticed that in the configuration FREESTREAM_TEMPERATURE= 843.33 (K) which is the total_temperature, not the static one.

The SU2 documentation is not strictly univocal as, for example in : SU2 Physical Definition FREESTREAM_TEMPERATURE is referred as static temperature, while in NICFD_nozzle tutorial it is referred as stagnation temperature (and I can tell that this tutorial is somewhat similar to the run @bgulzar22 is carrying out).

I understand that this parameters drive the initialization of the simulation, so at the end, the solution will be driven by the Boundary Conditions, anyways, can anybody please check/clarify on that?

Ok, nevermind, I noticed that the MACH_NUMBER is close to 0 so the configuration is initializing with stagnation conditions the flow ( total pressure and temperature, 0 velocity), and then let expand out ...
It might be because, mach number at the inlet of the nozzle is around 0 , so flow is static , so at this stage stagnation pressure will be equal to static pressure.
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Old   January 9, 2024, 04:28
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Quote:
Originally Posted by giovanni.medici View Post
Sorry for the slight detour on this topic, but I noticed that in the configuration FREESTREAM_TEMPERATURE= 843.33 (K) which is the total_temperature, not the static one.

The SU2 documentation is not strictly univocal as, for example in : SU2 Physical Definition FREESTREAM_TEMPERATURE is referred as static temperature, while in NICFD_nozzle tutorial it is referred as stagnation temperature (and I can tell that this tutorial is somewhat similar to the run @bgulzar22 is carrying out).

I understand that this parameters drive the initialization of the simulation, so at the end, the solution will be driven by the Boundary Conditions, anyways, can anybody please check/clarify on that?

Ok, nevermind, I noticed that the MACH_NUMBER is close to 0 so the configuration is initializing with stagnation conditions the flow ( total pressure and temperature, 0 velocity), and then let expand out ...
Hi, The freestream temperature is used to initialize the solution. In general, the freestream conditions are used as initial solution.
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Old   January 9, 2024, 05:40
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Let us know the progress, would be nice to see some more comparison with the measurements.
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