# Oscillating behaviour when mesh gets too small

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January 9, 2014, 06:04
Oscillating behaviour when mesh gets too small
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James B
Join Date: Oct 2013
Posts: 4
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Dear Foamers

I am simulating detonations with a 2nd order approximate Riemann Solver. The results are smooth when I have a relative coarse mesh size of 1 mm but when I refine my mesh the solver starts to oscillate in every variable (see figure), would you have any idea on how to solve this problem or where it comes from ? (Maybe adapting the FVScheme and add more dissipation)?
The mesh is a 1D shocktube (1 cell with upper and lower BC symmetry conditions imposed)

Thank you very much!!

Here is the FvScheme from DDTFoam

Code:
```ddtSchemes
{
default         Euler;
}

{
default         Gauss linear;
}

divSchemes
{
default         none;

div(tauShear)            Gauss linear;
div(tauMC)                Gauss linear;
div((tauShear&U))        Gauss linear;
div((p*U))            Gauss linear;

div(U)                 Gauss linear;

div(phiSt,c)        Gauss vanLeer01;
div(phiXi,Xi)    Gauss vanLeer;

div(phi,k)              Gauss upwind;
div(phi,epsilon)     Gauss upwind;
div(phi,omega)     Gauss upwind;
}

laplacianSchemes
{
default         Gauss linear corrected;
}

interpolationSchemes
{

default none;

interpolate(tauMC) Gamma phi 1.0;
interpolate(mu) Gamma phi 1.0;
interpolate(muEff) Gamma phi 1.0;

reconstruct(rho) limitedLinear 1.0;
reconstruct(U)   limitedLinearV 1.0;
reconstruct(T)   limitedLinear 1.0;

interpolate(rho) linear;         // for CFL
reconstruct(cSound) linear;     // for CFL

interpolate(p) linear;           // for MinMax scheme
interpolate(Teff) linear;         // for MinMax scheme
interpolate(tau) linear;          // for MinMax scheme

interpolate((((p*psiu)*sL)*Xi)) linear;
interpolate((sL*((1|Xi)-Xi))) linear;
interpolate(((rhoUnburned*sL)*Xi)) linear;
}

{
default         corrected;
}```
Attached Images
 oscillations.png (83.8 KB, 21 views)

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