Hello Foamers , I am making a 2D airfoil simualtion for an airfoil using both simpleFoam (steadyState) and pimpleFoam (transient) i ve generated my mesh uding Gambit than converted it to Openfoam .

I want to calculate the Cd Cl and Cm aerodynamic Coefficient and i am using the K-Omega SST turbulence Model with wall functions (y+>30)

once i run the simualtion for different angles of attack ( alpha > 8 ) i get Cd Cl that are far from the experimental data

so i visualised the residuals in real time and i vve noticed that the residuals for pressure and velovity and are not getting anyLower than 0.1and 0.001 (like in the picture attached ).

and these are the files for my case in the system directory :

controlDict

Code:

application pimpleFoam; startFrom startTime; startTime 0; stopAt endTime; endTime 5; deltaT 1e-5; writeControl adjustableRunTime; writeInterval 1e-2; purgeWrite 0; writeFormat binary; writePrecision 10; writeCompression off; timeFormat general; timePrecision 6; runTimeModifiable true; adjustTimeStep yes; maxCo 0.9; functions { #includeFunc residuals forces { type forces; libs ("libforces.so"); writeControl timeStep; writeInterval 10; patches (wing); rho rhoInf; log true; rhoInf 1.2047; CofR (0 0 0); } forceCoeffs1 { // Mandatory entries type forceCoeffs; libs ("libforces.so"); patches (wing); // Optional entries // Field names p p; U U; rho rhoInf; rhoInf 1.2047; // rhoInf 1.204; // Reference pressure [Pa] pRef 0; // Include porosity effects? porosity no; // Store and write volume field representations of forces and moments writeFields yes; // Centre of rotation for moment calculations CofR (0 0 0); // Lift direction liftDir (0 1 0); // Drag direction dragDir (1 0 0); // Pitch axis pitchAxis (0 0 -1); // Freestream velocity magnitude [m/s] magUInf 10.578; // Reference length [m] lRef 1; // Reference area [m2] Aref 1; // Spatial data binning // - extents given by the bounds of the input geometry } }

fvShemes

Code:

ddtSchemes { default Euler; } gradSchemes { default Gauss linear; grad(p) Gauss linear; grad(U) Gauss linear; } divSchemes { default none; div(phi,U) Gauss linearUpwind grad(U); div(phi,k) Gauss limitedLinear 1; div(phi,omega) Gauss limitedLinear 1; div((nuEff*dev2(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear limited corrected 0.5; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } wallDist { method meshWave; }

fvSolution

Code:

solvers { "pcorr.*" { solver GAMG; tolerance 0.02; relTol 0; smoother GaussSeidel; } p { $pcorr; tolerance 1e-7; relTol 0.01; } pFinal { $p; tolerance 1e-7; relTol 0; } "(U|k|omega)" { solver smoothSolver; smoother symGaussSeidel; tolerance 1e-06; relTol 0.1; } "(U|k|omega)Final" { $U; tolerance 1e-06; relTol 0; } } PIMPLE { // correctPhi yes; nOuterCorrectors 2; nCorrectors 2; nNonOrthogonalCorrectors 2; } relaxationFactors { fields { p 0.3; } equations { "(U|k|omega)" 0.7; "(U|k|omega)Final" 1.0; } } cache { grad(U); }

I ve tried to increse the number of iterations of PIMPLE by setting nOuterCorrectors to 100 , and in the log display i can see that there is an improvement of the pressure residuals whith each iteration but after T= 0.09 s i ve noticed that in the final iteration the initial residuals jumps back up as you can see and the residuals continue to be the same for the rest of the simualtion (t =1.4 sec)

Code:

PIMPLE: Iteration 98 smoothSolver: Solving for Ux, Initial residual = 1.616474724e-11, Final residual = 1.616474724e-11, No Iterations 0 smoothSolver: Solving for Uy, Initial residual = 1.960368055e-12, Final residual = 1.960368055e-12, No Iterations 0 GAMG: Solving for p, Initial residual = 1.657865185e-05, Final residual = 3.719486792e-07, No Iterations 2 time step continuity errors : sum local = 4.844632515e-14, global = -9.071970864e-17, cumulative = -1.122173492e-10 GAMG: Solving for p, Initial residual = 1.642056378e-05, Final residual = 3.701244997e-07, No Iterations 2 time step continuity errors : sum local = 4.820884777e-14, global = -8.295166997e-17, cumulative = -1.122174321e-10 PIMPLE: Iteration 99 smoothSolver: Solving for Ux, Initial residual = 1.577131026e-11, Final residual = 1.577131026e-11, No Iterations 0 smoothSolver: Solving for Uy, Initial residual = 1.910454271e-12, Final residual = 1.910454271e-12, No Iterations 0 GAMG: Solving for p, Initial residual = 1.631649698e-05, Final residual = 3.667338769e-07, No Iterations 2 time step continuity errors : sum local = 4.776725338e-14, global = -8.843266574e-17, cumulative = -1.122175206e-10 GAMG: Solving for p, Initial residual = 1.616322336e-05, Final residual = 3.649894645e-07, No Iterations 2 time step continuity errors : sum local = 4.754015883e-14, global = -8.080533709e-17, cumulative = -1.122176014e-10 PIMPLE: Iteration 100 smoothSolver: Solving for Ux, Initial residual = 2.21101886e-11, Final residual = 2.21101886e-11, No Iterations 0 smoothSolver: Solving for Uy, Initial residual = 2.667586351e-12, Final residual = 2.667586351e-12, No Iterations 0 GAMG: Solving for p, Initial residual = 0.3573363803, Final residual = 0.002989077632, No Iterations 4 time step continuity errors : sum local = 4.237840817e-10, global = 6.188044041e-13, cumulative = -1.11598797e-10 GAMG: Solving for p, Initial residual = 0.08131779127, Final residual = 7.551108567e-07, No Iterations 22 time step continuity errors : sum local = 7.381833497e-14, global = -8.421218529e-16, cumulative = -1.115996391e-10 smoothSolver: Solving for omega, Initial residual = 1.444649303e-06, Final residual = 8.852480069e-08, No Iterations 1 smoothSolver: Solving for k, Initial residual = 2.061374964e-06, Final residual = 1.15509241e-07, No Iterations 1 ExecutionTime = 639.93 s ClockTime = 640 s forceCoeffs forceCoeffs1 write: Cm = -0.08949366665 Cd = 0.173624454 Cl = 1.367788881 Cl(f) = 0.5944007738 Cl(r) = 0.7733881071 Courant Number mean: 0.006269592047 max: 0.8947602155 deltaT = 0.0001149425287 Time = 0.091954

Do you hav nay idea about why is the pressure residuals not getting any lower residual values or do you have any ideas about how can i fixe the problem ?!!

thank you