Rayleigh Taylor Instability Challenge

1. Richtmyer-Meshkov instability

The RMI takes place when two fluids of unequal densities are impulsively accelerated . Such instability is generally associated with the formation of shock waves. This instability can be considered the impulse-acceleration limit of the Rayleigh-Taylor instability. A paractical application implication of this instability is in the formation of shock waves in scramjets where the fuel-oxidant interface is enhanced by the breakup of the fuel into fine droplets.

2. Objective : RT instability simulation for air and water in ansys fluent

Geometry : 20x20 squares of air and water , with water on top .

Mesh : Element sizes considered were 0.5mm , 0.4mm and 0.6mm

Solver : Laminar

Analysis type: Transient , time step =0.005

Mesh-0.4mm

Animation

Mesh-0.5mm

Animation

Mesh -0.6mm

Animation

3.Objective: RTI simulation for user-defined fluid and Air

Refined mesh used is the same as the 0.5mm mesh

Animation

4. Atwood number

The Atwood number is a non-dimensional number used to characterise hydrodynamic instabilities.

It is defined as the ratio of diferrence of the fluid densities and the sum of the fluid densities.

For the first case with heavier fluid at 997 kg/m3 and lighter fluid at 1.223 kg/m3 the Atwood number is 0.995

For the sceond case it is 0.9938