Flow over a cylinder
Aim: To perform flow simulation over cylinder
Objective:
To perform flow analysis for certain flow velocity and then Reynold number is to be increased by 20%, 40% and 100% to study its effect.
Theory:
Reynold number is given by the equation,
`Re = (rho v D)/mu`
where,
`rho` = Density of working fluid (`(kg)/m^3`)
`v` = Velocity of flow (`m/s`)
`D` = Diameter of cylinder (`m`)
`mu` = Dynamic viscosity of working fluid (`Pa*s`)
For this study,
Diameter of cylinder = 25mm
Length of cylinder = 100mm
Working Fluid = Air
Initial inlet velocity = 1 `m/s`
For Air,
`rho` = 1.2 `(kg)/m^3`
`mu` = 0.0000181 `Pa*s`
Reynolds number for `v` = 1m/s,
Re = 1657.46
Velocities for change in Reynold number are given below,
| Sr. No. | % Increase in Reynolds Number | Velocity(m/s) |
| 1 | 20 | 1.2 |
| 2 | 40 | 1.4 |
| 3 | 100 | 2 |
Analysis Setup:
Create an time depenedent external flow simulation using wizard. Setup air as working fluid and enter 1m/s for initial velocity in x-direction. Setup flow for a duration twice the flow through time. Flow through time is the time required for fluild to flow from inlet to outlet. The length of the computational domain is choosen as 300mm with appropriate width and height.
Flow through time for different conditions is given below,
| Sr. No. | Velocity(m/s) | Flow through time(sec) |
| 1 | 1 | 0.3 |
| 2 | 1.2 | 0.25 |
| 3 | 1.4 | 0.215 |
| 4 | 2 | 0.15 |
The model for simulation is as shown below,
Results:
Case 1: v = 1m/s
Velocity:
Pressure:
Case 2: v = 1.2m/s
Velocity:
Pressure:
Case 3: v = 1.4m/s
Velocity:
Pressure:
Case 4: v = 2m/s
Velocity:
Pressure:
Conclusion:
It can be concluded form the results that as Reynold number is increased, velocity increases proportionally and flow changes from laminar to turbulent. In this study the reynold number was not such high that turbulent flow can be observed but laminar and transition flow was observed.