Week 5 - Rayleigh Taylor Instability
Aim:-To perform rayleigh taylor instability simulation for two different mesh sizes.
Theory
Rayleigh taylor instability :-it is an instability of an interference between two fluids of different densities which occurs when the lighter fluid pushes the heavier fluid.
at wood number :- it is a dimensionless number fluid dynamics used in the study of hydrodynanmic instabilities .
A = pi-p2/pi+p2
p1 = density of heavier fluid
p2 = density of light fluid
some practical cfd model based on the mathematical analysis ofrayleigh taylor waves
1.plateau-rayleigh instability :-
This instability explainswhy and how a falling a steam of fluid breaks up into smallrier packets.with the some volume but less surface area .it is releted to the rayleigh taylor instability.
2.Richtmyer - meshkov istability :-the richtmyer -mesh kov instability (RMI) occur when two fluids of different density impulsively accelerated.Normally this is by the passage of shock wave
procedure
Geometry
The geometry was constructedin spaceclaim for both the top and bottom fluid surfaces having dimension 20mm*20mm using.The pull tool, the geometry was converted to a 2d surface.And in order to have a conformal mesh.share taplology was enabled
Results
case 1
mesh size= 0.5 mm
primary phase -air
secondary phase =water
time step size - 0.005
no of time steps = 1000
link of animation file
At wood number calculation
p1 = 998.2 kg/m2
p2 = 1.225 kg/m3
A =008.2-1.225/008.2+1.225
A=0.907
case 2
mesh size= 0.2mm
primary phase -air
secondary phase =water
time step size - 0.0055
no of time steps = 1000
link of animation file
At wood number calculation
p1 = 998.2 kg/m2
p2 = 1.225 kg/m3
A =008.2-1.225/008.2+1.235
A=0.917
case 3
mesh size= 0.2mm
primary phase -air
secondary phase =water
time step size - 0.0055
no of time steps = 1000
link of animation file
At wood number calculation
p1 = 998.2 kg/m2
p2 = 400kg/m3
A =008.2-400/008.2+400
conclusion
.A finer mesh capture the instability more properly than a coarse mesh.
A transient approach is preferred since the instability simulation occur in an unpredictable manner and changes as a function of time
higher at wood number refers toi a higher rate of mixing, and the instability begins with a bubble like formation.
lower at wood number refers to a lower rate mixing and instabilty begins with formation.