# Discontinuity at the blunt trailing edge of an airfoil

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October 28, 2020, 04:42
Discontinuity at the blunt trailing edge of an airfoil
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Hey Foamers,

I am a beginner to openFoam and CFD. My research project is to study the airframe noise produced near the blunt trailing edge of a NACA 0012 airfoil.

I am trying to run a transient compressible simulation on openFoam, using rhoPimpleFoam as the solver and kOmegaSST as the turbulence model.

There is some discontinuity of pressure at the trailing edge, (likely induced by numerical instability). (See pics). In the early stage of computation, there is still some vortex shedding pattern near the trailing edge. In the later stage of computation, the vortex shedding disappears and there are only lines of discontinuity of pressure.

I am not sure what have I done wrong that causes such a discontinuity. I defined the initial alpha, k, nut, omega, p, T, U based on the rhoPimpleFoam/RAS/aerofoilNACA0012 tutorial. The value of k/nut/omega should be alright since I already have a successful transient incompressible simulation using pisoFoam.

The structured mesh should not be an issue, since it is built based on a reference article. I have turned on the adjustTimeStep and fixed the maxco to 0.5, so it should not be the problem of CFL. I guess it may be related to the fvSchemes or fvSolutions, but I am not sure.

Here are the numerical schemes I used.
////
ddtSchemes
{
default backward;
}

{
default Gauss linear;
}

divSchemes
{
default none;

turbulence Gauss upwind;
energy Gauss upwind;

div(phi,k) \$turbulence;
div(phi,omega) \$turbulence;

div(phi,e) \$energy;
div(phi,K) \$energy;
div(phi,Ekp) \$energy;

div(phiv,p) Gauss upwind;
div((phi|interpolate(rho)),p) Gauss upwind;

}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default linear;
}

{
default corrected;
}

wallDist
{
method meshWave;
}
/////

Here are the solvers that I used.
/////
solvers
{
p
{
solver GAMG;
smoother GaussSeidel;
tolerance 1e-6;
relTol 0.01;
}

pFinal
{
\$p;
relTol 0;
}

"(rho|U|k|omega|e)"
{
solver smoothSolver;
smoother GaussSeidel;
nSweeps 2;
tolerance 1e-08;
relTol 0.1;
}

"(rho|U|k|omega|e)Final"
{
\$U;
relTol 0;
}
}

PIMPLE
{
nCorrectors 2;
nNonOrthogonalCorrectors 1;
nOuterCorrectors 1;
}
/////

I am wondering if any of you encounter a similar problem before or have any idea what should I do to get rid of this discontinuity?

Many thanks!!!

-klkl
Attached Images
 discontiuity-1.jpg (32.5 KB, 19 views) discontiuity-2.jpg (41.0 KB, 14 views) flow.jpg (27.6 KB, 10 views) mesh.jpg (100.9 KB, 10 views)