CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   Main CFD Forum (https://www.cfd-online.com/Forums/main/)
-   -   What's the causes of numerical oscillation? (https://www.cfd-online.com/Forums/main/67909-whats-causes-numerical-oscillation.html)

What's the causes of numerical oscillation?

What's the causes of numerical oscillation?

By taking the Fourier transformation, I find an oscillation in my solution with scaled wavenumber 3.14.

How such things can happen? I am using centered difference and RK method.

 shyamdsundar September 2, 2009 23:00

I am not sure about the scaled wave number. Is it with respect to the cell width?

Anyway, I will try to provide a few points for cause of oscillations.

1)
In CFD, oscillations mostly occur at discontinuities. While solving, the numerical schemes try to fit the solution with a function, the degree of which would determine the order of the underlying scheme. Now, in the presence of discontinuities, a function approximation near the discontinuous solution would result in the so called Gibbs phenomenon. This becomes much more serious with higher order schemes.

2)
Oscillations can also occur due to the flux approximations. A less diffusive HLLC scheme would have more oscillations than the diffusive Lax Friedrich flux.

3)
Depending on the stability of numerical scheme, the (unstable) schemes could support certain modes of oscillations which can grow in time. A weakly unstable scheme can provide a better CFL limit, but would need some way of dissipating the unstable waves. For a central difference scheme, this would not be the case.

 drhim86 May 7, 2012 00:38