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February 28, 2013, 17:17 
Turbulent flow at low Mach number

#1 
Member
Roberto Pieri
Join Date: Feb 2012
Location: Milan
Posts: 57
Rep Power: 5 
Hello,
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:
Thank you in advance, Roberto 

March 4, 2013, 11:42 

#2 
Member
Roberto Pieri
Join Date: Feb 2012
Location: Milan
Posts: 57
Rep Power: 5 
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. 

March 6, 2013, 12:22 

#3  
Super Moderator
Francisco Palacios
Join Date: Jan 2013
Location: Stanford, CA
Posts: 301
Rep Power: 5 
Quote:
Could you please download the last version of the code (it contains some relevant improvements with respect the previous one) http://su2.stanford.edu/download/svn/SU2_Rev1206.zip 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. Best, Francisco 

March 7, 2013, 10:34 

#4 
Senior Member
Samuele Z
Join Date: Oct 2009
Location: Mozzate  Co  Italy
Posts: 490
Rep Power: 9 
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: Code:
zampini@pczampini:~/SU2_Rev1206/SU2_Rev1206/NACA0012_RANS/comp$ SU2_CFD default_comp.cfg   SU2 Suite (Computational Fluid Dynamics Code)    Physical case definition  Continuous NavierStokes 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  JamesonSchmidtTurkel 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 NavierStokes eq. source terms. Gradient Computation using weighted LeastSquares method.  Time numerical integration  Local time stepping (steady state simulation). Euler implicit method for the adjoint equations. No CFL ramp. CourantFriedrichsLewy 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  NavierStokes wall boundary marker(s): airfoil. Farfield boundary marker(s): farfield.  Flow & Nondimensionalization 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): 1.853e05 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 nondimensional state: Mach number (nondimensional): 0.15 Reynolds number (nondimensional): 6e+06 Reynolds length (m): 1 Froude number (nondimensional): 16.6554 Specific gas constant (nondimensional): 0.999998 Freestream temperature (nondimensional): 1 Freestream pressure (nondimensional): 1 Freestream density (nondimensional): 1 Freestream velocity (nondimensional): (0.177482,0) > Modulus: 0.177482 Freestream energy (nondimensional): 2.51575 Freestream viscosity (nondimensional): 2.95804e08 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 (NavierStokes' equations). MG level: 0. Initialize jacobian structure (SA model).  Integration and solver preprocessing  Area projection in the yplane = 0.998982. Set NearField boundary conditions (if any). Set Interface boundary conditions (if any).  Begin solver  Single iteration of the direct solver to store flow data. [pczampini:08664] *** Process received signal *** [pczampini:08664] Signal: Segmentation fault (11) [pczampini:08664] Signal code: Address not mapped (1) [pczampini:08664] Failing at address: (nil) [pczampini:08664] [ 0] /lib/libpthread.so.0(+0xeff0) [0x7fc62c635ff0] [pczampini:08664] [ 1] SU2_CFD(_ZN11CNSSolution13PreprocessingEP9CGeometryPP9CSolutionPP9CNumericsP7CConfigt+0x199) [0x60ff19] [pczampini:08664] [ 2] SU2_CFD(_ZN21CMultiGridIntegration13FAS_MultigridEPPP9CGeometryPPPP9CSolutionPPPPP9CNumericsPP7CConfigtttmt+0x226) [0x493256] [pczampini:08664] [ 3] SU2_CFD(_ZN21CMultiGridIntegration19SetMultiGrid_SolverEPPP9CGeometryPPPP9CSolutionPPPPP9CNumericsPP7CConfigtmt+0x258) [0x491cb8] [pczampini:08664] [ 4] SU2_CFD(_Z20AdjMeanFlowIterationP7COutputPPP12CIntegrationPPP9CGeometryPPPP9CSolutionPPPPP9CNumericsPP7CConfigPP16CSurfaceMovementPP19CVolumetricMovementPPP14CFreeFormChunkm+0x2f9) [0x4a1e79] [pczampini:08664] [ 5] SU2_CFD(main+0x11a1) [0x6ad191] [pczampini:08664] [ 6] /lib/libc.so.6(__libc_start_main+0xfd) [0x7fc62c2e3c8d] [pczampini:08664] [ 7] SU2_CFD() [0x459109] [pczampini:08664] *** End of error message *** Segmentation fault zampini@pczampini:~/SU2_Rev1206/SU2_Rev1206/NACA0012_RANS/comp$ Thanks a lot, Samuele 

March 12, 2013, 01:56 

#5 
Super Moderator
Thomas D. Economon
Join Date: Jan 2013
Location: Stanford, CA
Posts: 260
Rep Power: 5 
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 ROE2ND_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. Cheers, Tom 

January 3, 2014, 04:18 

#6 
New Member
Caroline Chow
Join Date: Jan 2014
Posts: 1
Rep Power: 0 
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 04:07. 

Tags 
naca0012, subsonic, turbulent 
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