CFD - Flow over a cylinder

FLOW OVER A CYLINDER

Objective:

Simulate the flow of air over a cylinder of the given dimensions and to calculate the baseline case Reynolds number and then increase the Reynolds number by a factor of 20%, 40%, and 100% then run the transient flow simulation.

Formulae used :

• `Re = rho*u*D/mu`
• D = cylinder diameter
• mu = dynamic viscosity
• rho = density
• u = velocity of fluid

Procedure:

• The Cylinder is modelled in approximated dimensions on solidworks.
• Flow simultation is setup with External flow.
• Input velocity is varied according to the various reynolds number.
• The Mesh are defined to a suitable value to get a very accurate description
• The flow simulation is run after setting up necessary boundary conditions.
• The post processing data is obtained and the cut plots for velocity and pressure are derived.

Medium used is air, Hence the characteristics of air to find the baseline Reynolds number is as follows

• Diameter of cylinder : 1m
• Density of air : 2254 Kg/m^3
• Dynamic Viscosity of air : 81*10^-5 Kg/ms
• Baseline Velocity : 10 m/s
• Baseline Reynolds number :67701.65746

New Reynolds number and velocities

Case 1: Baseline Reynolds number

Velocity plot

Pressure Plot

Case 2: 20% Baseline Reynolds number

Velocity plot

Pressure Plot

Case 3: 40% Baseline Reynolds number

Velocity plot

Pressure Plot

Case 4: 100% Baseline Reynolds number

Velocity plot

Pressure Plot

Calculation of End Time simulation

Length of computational domain along X direction: 0.9m

Velocity	Flow through time	End time
10	0.09s	0.18s
11.99	0.075s	0.15s
13.99	0.064s	0.128s
19.99	0.045s	0.09s

Conclusion

Since in all 4 cases, the reynolds number is significantly much greater than 2300, it can be said that our study involves only turbulent flow.It can be noted that reynolds number is directly proportional to the velocity and the resulting cut plots and velocity parameters are evidence.