External Flow simulation over cylinder

Objective :

To simulate the flow over the cylinder for the baseline condition of speed to 10 m/s Diameter of 0.04m and length of 0.05m then calculating the Reynolds number for baseline condition and then increase the Reynolds number by a factor of 20%, 40%, and 100% then run the transient flow simulation and Simulation end time should be calculated properly.

Calculation :

Calculating the Reynolds number for the baseline condition

We know,

here rho = 1.225 kg/m^3

velocity = 10 m/s

Diameter = 0.04 m

Therefore Re = 26849.31 Here we got the Re number for the baseline condition

Therefore now Reynolds number for the

• case 1 (With the increase of Re by 20 %) : 32219.172
• case 2 (With the increase of Re by 40 %) : 37589.034
• case 3 (With the increase of Re by 100 %) : 53698.62

Now using the same formula we calculate the input velocity for

• case 1 = 12m/s
• case 2 = 14m/s
• case 3 = 20m/s

After running the baseline simulation we take the total length of computational domain in the x-direction is 1.5m taking 1.25 and -0.25

For calculating the end time we know,

time (t) = Lenght (l) / Velocity

End time = 2 * t

for the time step we are taking the overall 10 time steps, therefore

time step = end time / 10

Therefore end time and time step at

• baseline = 0.3s , 0.03
• case 1 = 0.25 , 0.025
• case 2 = 0.21 , 0.021
• case 3 = 0.15 , 0.015

Modelling and setting up the flow simulation :

• With the dimension of the circle we sketch and extrude to form the 3D component
• now we create the wizard and select the external flow and give time dependence and give end time and time step input
• we are selecting the time dependence because we want to have the transient flow simulation
• After that, we input the value of velocity perpendicular to the cylinder
• After setting up the wizard we change the computational domain
• now we refine the mesh and create the local mesh to have better results

Results :

• At baseline

Pressure: https://youtu.be/drs3iOzEVWc

Velocity : https://youtu.be/ZWdOO6UUGkw

• at case 1

Pressure: https://youtu.be/NeVx5kERqnc

velocity:https://youtu.be/6FRedB6c1I0

• case 2

Pressure: https://youtu.be/EzkCnJzn5Ig

Velocity: https://youtu.be/1iHqdFPJEF0

• case 3

Pressure: https://youtu.be/BW3RanBzZGI

Velocity: https://youtu.be/Epc78XcUpv0

Conclusion:

As the Reynolds number increases the flow tends to become more transient wherever the change in pressure is not big as compared to the change in the velocity which shows the effect of Reynolds number on velocity and pressure.