Rayleigh Taylor Instability

Rayleigh Taylor Instability

Description:

Rayleigh Taylor instability is an instability of an interface between two fluids of different densities.It occurs typically when the heavier fluid is supported by the lighter fluid.

Atwood number:

It is defined as the ratio between the difference in two densities to their sum.It is a dimensionless number.

A=`rho1`-`rho2`/`rho1`+`rho2`

`rho1`- density of the heavier fluid.

`rho2`- density of the lighter fluid.

Steps in Analysis of Rayleigh Taylor Instability:

• Geometry
• Meshing
• Set up
• Solution
• Result

Geometry:

• Creation of 2D model.
• Share topology.

1.Creation of 2D model:

The first step in this case this to create a 2D geometry.The 2D geometry is created by using the rectangle command.At first two rectangles has to be created and then the line diagram is coverted into surface by using pull tool.

2.Share topology:

The information between the two medium is shared by using share command.

Meshing:

The rectangle surface is discretized into a small elements of size 0.0005m.

• No of elements=3200.
• No of nodes =3321.

Set up:

The set up for this case as follows,

General :1.Pressure based solver

2.Transient condition

3.Gravity-Y-axis= -9.81

Model :1.Multiphase-On-Volume of fluid

2.Viscous-Laminar flow

Material :1.Fluid-Air & Water liquid

Cell zone condition :1.Air-Fluid-air

2.Water surface-Fluid-water liquid

Initialization :1.Standard initialization

2.Patch

Atwood number calculation:

• Density of the water = 998.2 Kg/m^3
• Density of the air = 1.225 Kg/m^3

Atwood number = 0.9975

Solution:

The calculation is set to run for,

• Time step size =0.005.
• No of time step=1000.

The calculation is converged in 750 iterations.

Result:

Phase contour:

Conclusion:

In this case the inteface of two different fluids (various densities) were analysed and Atwood number for this case is calculated.