Flow over a cylinder
Aim: CFD analysis of a cylinder in which external flow takes place and running a baseline simulation and then calculating the Reynolds number and also the simulation end time. Then increase the Reynolds number by a factor of 20%, 40%, and 100% then run the transient flow simulation. Animations for velocity for all the three Reynolds number calculated.
Theory:
Reynold's Number
Reynolds number can reveal whether the flow is laminar or turbulent. The transition from laminar to turbulent flow depends on the surface roughness, flow velocity, geometry, surface temperature, and type of fluid, among others.
`R=(rho*V*D)/v = (rho*V*D)/mu`
R= Reynolds Number
V= Velocity of Fluid
D= Diameter
`mu =` Dynamic Viscocity
v = kinematic Viscosity
The present study aims to analyze the fluid flow over a cylinder and calculate Reynold's number for baseline simulation and increase the calculated Reynolds number to a factor of 20%, 40%, & 100% and perform the simulation for all the three values of Reynold's number and create an animation file for velocity-pressure.
GEOMETRY OF THE MODEL
A cylinder is created in SOLIDWORKS. The design parameters are:
The diameter of the cylinder = 40 mm
Length of the cylinder = 50mm
Baseline Simulation Parameters:
Initial Velocity = 10 m/s
R = 40518.19
Similarly, Reynold's number at 20, 40 and 100 % is calculated,
At 20% R = 48621.83
At 40% R = 56725.46
At 100% R = 81036.38
Calculations:
Velocity = Distance / time
Time = Distance / velocity i.e. Time = 0.75/10 = 0.075 sec
The length of the domain along the X axis is 0.750 m
When the Velocity is 10 m/s for Re = 40518.19 then Simulation end time = 0.15 sec
Given that the end time should be 2 times the flow through time
At Baseline For V = 10 m/s , Re = 40518.19 , Simulation end time = 0.150 sec
At 20% For V = 12 m/s , Re = 48621.83 , Simulation end time = 0.125 sec
At 40% For V = 14 m/s , Re = 56725.46 , Simulation end time = 0.107 sec
At 100% For V = 20 m/s , Re = 81036.38 , Simulation end time = 0.075 sec
Results:
Flow over a cylinder at Baseline Velocity = 10m/s
Animation videos for velocity at 10 m/s and R = 40518.19
Flow over a cylinder at 20% of Reynolds Number i.e. at 12m/s:
- Cut Plot of Velocity contour
Animation videos for velocity at 12 m/s and R = 48621.83
Flow over a cylinder at 40% of Reynolds Number i.e. at 14m/s:
- Cut Plot of Velocity contour
Animation videos for velocity at 14 m/s and R = 56725.46
Flow over a cylinder at 100% of Reynolds Number i.e. at 20m/s
- Cut Plot of Velocity contour
Animation videos for velocity at 20 m/s and Re = 81036.38
Conclusion:
- As Reynold's number increases the Velocity increases and the flow-through time decreases.
- As the velocity or Renold's number increase, the flow over the cylinder becomes steady and the velocity plot at 20% and 40% exhibit slight unsteady plot whereas at 100%
- The flows are steady and we can draw a clear understanding of the flow when velocity is increased.