Flow over a cylinder
FLOW OVER A CYLINDER
AIM:
- Calculate the baseline case Reynolds number.
- Run a baseline simulation and then calculate the Reynolds number. Then increase the Reynolds number by a factor of 20%, 40%, and 100% then run the transient flow simulation.
- Simulation end time should be calculated properly
- Make sure that end time is set to 2 times flow through time.
- Create animations for pressure-velocity for all the three Reynolds numbers.
- Explain your observations
SPECIFICATION:
- Diameter of the cylinder - 40mm
- length of the cylinder - 50mm
- Surface roughness is taken as zero
- Gravity is not considered
Formula to calculate the baseline case Reynolds number:
- Re = rho*U_inlet*D/mu
- D = cylinder diameter
- mu = dynamic viscosity
- rho = density
PROPERTIES OF FLUID:
- Fluid - Air
- Density of air - 1.225 kg/m^3
- Dynamic viscosity of air - 1.81*10^-3 Kg/ms at temp 300K.
The velocity of air is calculated by the formula of Reynold's number.
CALCULATION:
- The computational domain has a length of 300mm.
- Thus the flow-through time is given as the time taken for the velocity to reach the end of the computational domain.
- The end time is taken as twice that of flow through time.
| Re | 20 | 40 | 40 |
| Velocity | 0.0074 | 0.0148 | 0.0369 |
| Flow-through time | 40.54 | 20.27 | 8.13 |
| End time | 81 | 40.54 | 16.26 |
While conducting the simulation wizard the total analysis time is equal to the end time obtained.
PRESSURE AND VELOCITY CUT PLOTS FOR RESPECTIVE REYNOLDS NUMBER:
For Re=20
Velocity plot
Variable pressure plot
For Re=40
Velocity plot
Variable pressure plot
For Re=100
Velocity plot
Variable pressure plot
Animation for different Re at 20, 40, 100.
At Re = 20
Velocity flow
Pressure flow
At Re = 40
Velocity flow
Pressure flow
At Re = 100
Velocity flow
Pressure flow