Transient flow over a cylinder based upon the change in Reynolds number

Aim: -

Simulating the transient flow over a cylinder.

Objectives: -

• Run a baseline simulation and then calculate the Reynolds number.
• Increase the Reynolds number by a factor of 20%, 40%, and 100% then run the transient flow simulation.
• Make sure that end time is set to 2 times flow through time.
• Create animations for pressure-velocity for all the three Reynolds number.

Assumptions: -

D = 0.02 m.

Fluid = air.

rho = 1.225 kg/m³

mu = 1.81 × 10^-5kg/(m. s)

Calculations:-

For the base line simulation the velocity is 10 m/s.

Formula to calculate Reynolds number is

Re = rho*U_inlet*D/mu

D = cylinder diameter

mu = dynamic viscosity

rho = density

Therfore the reynolds number is 13536.

By increasing the reynolds number by 20%, Re = 162432.2

V1 = 12 m/s.

By increasing the reynolds number by 40%, Re = 18950.4

V1 = 14 m/s.

By increasing the reynolds number by 100%, Re = 27072

V1 = 20 m/s.

Steps taken to solve the Problem.

• Initially I created the geometry with a diameter of 0.02 m and extruded to 1 m.
• After that I used the solidworks flow simulation tool to setup the simulation.
• In the wizard i defined the flow as external and time dependent with total analysis time as 1s and Output time step as 0.02s.
• Finally I defined the velocity as 10 m/s.
• After that I ran the analysis.
• Then created cut plots to represent velocity and pressure.
• After that by using parametric study I defined the values of various velocities.
• And finally ran the analysis to get the plots.

Results: -

For 10 m/s velocity,

Velocity Plot

Pressure Plot

Velocity and Pressure plot formation on the cylinder with 10 m/s velocity.

For 12 m/s velocity,

Velocity Plot

Pressure Plot

Velocity and Pressure plot formation on the cylinder with 12 m/s velocity.

For 14 m/s velocity,

Velocity Plot

Pressure Plot

Velocity and Pressure plot formation on the cylinder with 14 m/s velocity.

For 20 m/s velocity,

Velocity Plot

Pressure Plot

Velocity and Pressure plot formation on the cylinder with 20 m/s velocity.

Conclusion: -

• By looking at the velocities we come to a conclusion that as the velocity increases the speed of the wind at the back of the cylinder decreases as the layers of wind above and below forces the wind to flow in a faster.
• In the same way as we look at the pressure plots we can conclude that the pressure force acting at the frontal area of the cylinder keeps on increasing, but at the sides and the rear of the cylinder the pressure force is pretty low.