# Rayleigh Taylor Instability (2D) using Multicomponent2D shan chen model

Posted by vishwesh
 Rayleigh Taylor Instability (2D) using Multicomponent2D shan chen model February 16, 2018 09:09AM Registered: 1 year ago Posts: 13
Hi!

I am trying to validate the multicomponent2D- rayleigh taylor code given in palabos show cases using this paper. There are several queries that I have regarding this:

1. The paper mentions:

Quote

The initial perturbation of the interface is a sinusoidal function, with amplitude A = 0.1W and wavelength λ = 2π/W

When I refer to the current code, the interface is defined using the following piece of code:

```Language: C++    // Initialize top layer.
applyIndexed(heavyFluid, Box2D(0, nx-1, 0, ny-1),
new TwoLayerInitializer<T,DESCRIPTOR>(ny, true) );
// Initialize bottom layer.
applyIndexed(lightFluid, Box2D(0, nx-1, 0, ny-1),
new TwoLayerInitializer<T,DESCRIPTOR>(ny, false) );```

Considering that I do know the equation for the interface which will be a function of x, how can I initialize the interface according to this?

2. Also, the paper does not mention about perturbation due to density variation so I changed the densityFluctuation to 0. Will it cause any problems?

3. The computational domain in the paper has been described to be W = 100 and height = 4W = 400. Also, the grid has also been defined. But, in the current example, the domain size is defined by nx and ny and changing them is the only way to change the domain as well as the mesh. Any other way to resolve it?

4. I referred to a paper on Shan-Chen model which described G to be a quantity which defines the interaction between the fluids. Also, according to the paper, G value cannot be calculated using a formula. If this is the case then how did we arrive to G=0.15

5. Why is gravity defined to be 0.45/ny? Has this been done to make the quantity dimensionless? If that's the case, how did we arrive to 0.45?

I would be really grateful for any help I can get regarding this matter.