Flow over a cylinder

AIM:-

To calculate the baseline case Reynold’s number and perform simulation with animation of transient flow condition over cylinder.

INTRODUCTION:-

In this project I am going to simulate the flow over a cylinder and then calculate the base line Reynold’s Number. Then increase the Reynold’s number by a factor of 20%, 40% and 100%, the run transient flow simulation.

THEORY:

Reynold’s number is an important dimensionless quantity in fluid mechanics used to help predict flow patterns in different fluid flow situations. It is the ratio of inertial forces to viscous forces. Reynold number can reveal whether the flow is laminar or turbulent.

Re_D = `rho``V``D`/`mu`

Where,

Re_D = Reynold’s number (Dimensionless number)

V = average velocity (m/s)

D = diameter (m)

µ = viscosity of fluid (dynamic) (Pa-s)

PROCEDURE:-

CALCULATION:

Input values:

D = 0.02*2 = 0.04 m

V = 10 m/s

ρ = 1.225 kg/m³

µ = 1.81*10^-5 Pa-s

upon substitution

Re = 27071

Similarly at 20 %

Re = 32485

Similarly at 40 %

Re = 37899

Similarly at 100 %

Re = 54142

Now performed baseline simulation with following conditions:

Analysis type :- External Flow

Fluid under consideration : Air

Time Dependent : Total analysis time = 0.1 s

Output time step = 0.01 s

Inlet velocity ( x-direction) = 10 m/s

Simulation End time calculations:

Time = Distance / velocity

Time = 0.6/10 = 0.06 sec (Domain length along x-axis is taken to be 0.6 m)

At baseline for v = 10 m/s, simulation end time = 2*0.06= 0.120 sec

At 20 % for v = 12 m/s, Re = 32485, Simulation end time = 0.100 sec

At 40 % for v = 14 m/s, Re = 32485, Simulation end time = 0.085 sec

At 100 % for v = 20 m/s, Re = 32485, Simulation end time = 0.060 sec

So velocity is increasing as the time is decreasing.

OBSERVATION:-

(1).figure showing cut plot with velocity contour at baseline velocity of 10 m/s

corresponding animation video

Cut plot for pressure

Corresponding Pressure animation video

(2).figure showing cut plot with velocity contour at baseline velocity of 12 m/s

corresponding animation video

Cut plot for pressure

Corresponding Pressure animation video

(3).figure showing cut plot with velocity contour at baseline velocity of 14 m/s

corresponding animation video

Cut plot for pressure

Corresponding Pressure animation video

(4).figure showing cut plot with velocity contour at baseline velocity of 20 m/s

corresponding animation video

Cut plot for pressure

Corresponding Pressure animation video

RESULT:-

Upon simulation and then analysing results it is found that as the velocity increases, Reynolds number increases and corresponding simulation time is decreased. And as the velocity was increased the flow over the cylinder became steady.