Flow over cylinder Steady and Unsteady flow

1] Steady Mode

Vertex Average of velocity Magnitude

Left Coefficient (Cl)

From the above graphs, Vertex average of velocity and lift coefficient fluctuate in non periodicaly upto 360 to 400 iteration, after that vertex avarage of velocity and lift coefficient fluctuate in periodicaly in a fix interval of time and rate of fluctuation is constant. Means we can say that the flow has converged after 400 iteration

2] Unsteady Mode

Vertex Average of velocity

Lift Coefficient

From the above graphs, Vertex Average of Velocity and lift coefficient fluctuate non periodicaly upto flow time(s) 125 , after that they fluctuate periodicaly in fix interval of time means rate of fluctuation is constant. so we can conclude that flow has converged after flow time (s) 120.

so we can say that if the fluctuation of velocity is periodic i e rate of fluctuation is constant, then the flow has converged.

Strouhal number calculation:

For Unsteady flow

St =(f *D)/U f: frequency(1/s) D: characteristic length (m)

U: Velocity air flow (m/s)=1

from the above graph,

when the flow has converged , 8 peak occure in 95 sec , so the frequency is 0.08425

i e f=0.08425 then St= (0.08425*2)/1

= 0.1685

Strouhal Number is 0.1685