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Old   February 28, 2013, 16:17
Default Turbulent flow at low Mach number
Roberto Pieri
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I am trying to simulate the turbulent flow around airfoil NACA0012 at low Mach number (say M=0.15) and Re=6e6 in order to perform a shape optimization, then I also need adjoint simulation (impossible with the incompressible formulation, is it right?).
Up to now, I don't have a satisfying enough solution in terms of pressure distribution. I have some questions:
  • Do you have any advice to build a good mesh? My mesh:
  • From your twitter account, I notice that you are validating low Mach cases. Do you have any suggestion to run my case? (space and time discretization, multigridů)

Thank you in advance,
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Old   March 4, 2013, 10:42
Roberto Pieri
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Referring to your last tweet, can you please give me some information about the settings used to have that results?
I am trying to reproduce the same case, but the pressure distribution has a strange behavior near leading edge, as you can see from the Cp plot I attach.
Attached Files
File Type: pdf Cp.pdf (43.4 KB, 51 views)
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Old   March 6, 2013, 11:22
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Francisco Palacios
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Originally Posted by robyTKD View Post
Referring to your last tweet, can you please give me some information about the settings used to have that results?
I am trying to reproduce the same case, but the pressure distribution has a strange behavior near leading edge, as you can see from the Cp plot I attach.
Thanks Roberto,
Could you please download the last version of the code (it contains some relevant improvements with respect the previous one)

after unzipping the code you will find a folder called NACA0012_RANS with the files that we have used for the compressible and incompressible validation.

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Old   March 7, 2013, 09:34
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Samuele Z
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Hi Francisco and thanks for the new version of the solver.

I ran it and both the compressible and incompressible cases work well.

The point is that I try to solve the adjoint problem (either compressible or incompressible), I can not run it and I get this error:

zampini@pc-zampini:~/SU2_Rev1206/SU2_Rev1206/NACA0012_RANS/comp$ SU2_CFD default_comp.cfg 

|             SU2 Suite (Computational Fluid Dynamics Code)             |

------------------------ Physical case definition -----------------------
Continuous Navier-Stokes adjoint equations with frozen viscosity.
Mach number: 0.15.
Angle of attack (AoA): 0 deg, and angle of sideslip (AoS): 0 deg.
Reynolds number: 6e+06.
No restart solution, use the values at infinity (freestream).
Read flow solution from: solution_flow.dat.
Surface(s) where the force coefficients are to be evaluated: airfoil.
The reference length/area (force coefficient) is 1.
The reference length (moment computation) is 1.
Reference origin (moment computation) is (0.25, 0, 0).
Input mesh file name: mesh_NACA0012_turb_897x257.su2

----------------------- Design problem definition -----------------------
Drag objective function.
Primitive variables gradient threshold: 100.

---------------------- Space numerical integration ----------------------
Jameson-Schmidt-Turkel scheme for the adjoint inviscid terms.
JST viscous coefficients (1st, 2nd, & 4th): 0.15, 0, 0.02.
The method includes a grid stretching correction (p = 0.3).
Average of gradients with correction (viscous adjoint terms).
Piecewise constant integration of the Navier-Stokes eq. source terms.
Gradient Computation using weighted Least-Squares method.

---------------------- Time numerical integration -----------------------
Local time stepping (steady state simulation).
Euler implicit method for the adjoint equations.
No CFL ramp.
Courant-Friedrichs-Lewy number:        8

------------------------- Convergence criteria --------------------------
Maximum number of iterations: 99999999999.
Reduce the adjoint density residual 6 orders of magnitude.
The minimum value for the adjoint density residual is 10^(-10).

-------------------------- Output information ---------------------------
Writing a flow solution every 5000 iterations.
Writing the convergence history every 1 iterations.
The output file format is Paraview (.vtk).
Convergence history file name: history.
Adjoint solution file name: solution_adj.dat.
Restart adjoint file name: restart_adj.dat.
Adjoint variables file name: adjoint.
Surface adjoint coefficients file name: surface_adjoint.
Surface(s) to be plotted: airfoil.

------------------- Config file boundary information --------------------
Navier-Stokes wall boundary marker(s): airfoil.
Far-field boundary marker(s): farfield.

---------------- Flow & Non-dimensionalization information ---------------
Viscous flow: Computing pressure using the ideal gas law
based on the freestream temperature and a density computed
from the Reynolds number.
--Input conditions:
Grid conversion factor to meters: 1
Ratio of specific heats: 1.4
Specific gas constant (J/(kg.K)): 287.87
Freestream pressure (N/m^2): 184090
Freestream temperature (K): 300
Freestream density (kg/m^3): 2.13163
Freestream velocity (m/s): (52.1572,0) -> Modulus: 52.1572
Freestream energy (kg.m/s^2): 217263
Freestream viscosity (N.s/m^2): 1.853e-05
--Reference values:
Reference pressure (N/m^2): 184090
Reference temperature (K): 300
Reference energy (kg.m/s^2): 86361.1
Reference density (kg/m^3): 2.13163
Reference velocity (m/s): 293.873
Reference viscosity (N.s/m^2): 626.428
--Resulting non-dimensional state:
Mach number (non-dimensional): 0.15
Reynolds number (non-dimensional): 6e+06
Reynolds length (m): 1
Froude number (non-dimensional): 16.6554
Specific gas constant (non-dimensional): 0.999998
Freestream temperature (non-dimensional): 1
Freestream pressure (non-dimensional): 1
Freestream density (non-dimensional): 1
Freestream velocity (non-dimensional): (0.177482,0) -> Modulus: 0.177482
Freestream energy (non-dimensional): 2.51575
Freestream viscosity (non-dimensional): 2.95804e-08
Force coefficients computed using freestream values.

---------------------- Read grid file information -----------------------
Two dimensional problem.
57824 points.
57344 interior elements. 2 surface markers.
704 boundary elements in index 0 (Marker = farfield).
256 boundary elements in index 1 (Marker = airfoil).

------------------------- Geometry preprocessing ------------------------
Setting local point and element connectivity.
Checking the numerical grid orientation.
Identifying edges and vertices.
Computing centers of gravity.
Setting the control volume structure.
Area of the computational grid: 875555.
Searching for closest normal neighbor on the surface.
Searching for sharp corners on the geometry.

------------------------- Solution preprocessing ------------------------
Initialize jacobian structure (Navier-Stokes' equations). MG level: 0.
Initialize jacobian structure (SA model).

------------------ Integration and solver preprocessing -----------------
Area projection in the y-plane = 0.998982.
Set Near-Field boundary conditions (if any).
Set Interface boundary conditions (if any).

------------------------------ Begin solver -----------------------------
Single iteration of the direct solver to store flow data.
[pc-zampini:08664] *** Process received signal ***
[pc-zampini:08664] Signal: Segmentation fault (11)
[pc-zampini:08664] Signal code: Address not mapped (1)
[pc-zampini:08664] Failing at address: (nil)
[pc-zampini:08664] [ 0] /lib/ [0x7fc62c635ff0]
[pc-zampini:08664] [ 1] SU2_CFD(_ZN11CNSSolution13PreprocessingEP9CGeometryPP9CSolutionPP9CNumericsP7CConfigt+0x199) [0x60ff19]
[pc-zampini:08664] [ 2] SU2_CFD(_ZN21CMultiGridIntegration13FAS_MultigridEPPP9CGeometryPPPP9CSolutionPPPPP9CNumericsPP7CConfigtttmt+0x226) [0x493256]
[pc-zampini:08664] [ 3] SU2_CFD(_ZN21CMultiGridIntegration19SetMultiGrid_SolverEPPP9CGeometryPPPP9CSolutionPPPPP9CNumericsPP7CConfigtmt+0x258) [0x491cb8]
[pc-zampini:08664] [ 4] SU2_CFD(_Z20AdjMeanFlowIterationP7COutputPPP12CIntegrationPPP9CGeometryPPPP9CSolutionPPPPP9CNumericsPP7CConfigPP16CSurfaceMovementPP19CVolumetricMovementPPP14CFreeFormChunkm+0x2f9) [0x4a1e79]
[pc-zampini:08664] [ 5] SU2_CFD(main+0x11a1) [0x6ad191]
[pc-zampini:08664] [ 6] /lib/ [0x7fc62c2e3c8d]
[pc-zampini:08664] [ 7] SU2_CFD() [0x459109]
[pc-zampini:08664] *** End of error message ***
Segmentation fault
Any idea about how to solve this?

Thanks a lot,
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Old   March 12, 2013, 00:56
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Thomas D. Economon
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Hi Samuele,

Could you please check that you are using the same spatial discretization for both the flow and adjoint problems in the config file (i.e. use either JST or ROE-2ND_ORDER for both CONV_NUM_METHOD_FLOW and CONV_NUM_METHOD_ADJ)? Could you also please check that they are both using the same type of time integration (i.e. both EULER_IMPLICIT for instance)?

In general, you are not required to use the same scheme, however we recently discovered a small issue in the config options which will be fixed in the next release. For now, this should fix your problem, I think.

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Old   January 3, 2014, 03:18
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Caroline Chow
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I write a post here but then I searched the forum and its already been solved. so can anyone delete this post for me pls? thanks.

Last edited by Caroline; January 6, 2014 at 03:07.
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naca0012, subsonic, turbulent

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