Flow over a cylinder
Objective: The following objectives are carried on a cylinder.
- Calculate the Reynolds number for the baseline simulation.
- Run a baseline simulation.
- Run a transient flow simulation for an increasing reynolds number by a factor of 20%, 40%, 100% of the baseline reynolds number.
- Create animations for pressure-velocity for all the three Reynolds number.
Assumptions:
- Surface of cylinder is smooth and roughness is considered zero.
- Effects of temperature are not considered in study.
- Cylinder diameter= 0.04 m.
- Cylinder length= 0.06 m.
- Computational domain in x-direction=0.6 m.
Calculations:
a) Baseline
- Re = rho*U-inlet*D/mu= 2166 (Laminar Region).
- D = cylinder diameter= 0.04 m.
- mu = dynamic viscosity= 1.81x10^(-5) Kg/ms.
- rho = density= 1.225 Kg/m^3.
- U-inlet=Inlet velocity= 0.8m/s.
b) For Re= 120%*2166= 2600.
Re = rho*U-inlet*D/mu.
U-inlet = (2600*1.81x10^(-5)/1.225*0.04)
U-inlet = 0.96m/s.
Flow through time= Length of domain/Velocity.
FTT= 0.6/0.96= 0.625sec.
End time= FTT*2= 1.25sec.
c) For Re= 140%*2166= 3032.
Re = rho*U-inlet*D/mu.
U-inlet = (3032*1.81x10^(-5)/1.225*0.04)
U-inlet = 1.12m/s.
Flow through time= Length of domain/Velocity.
FTT= 0.6/1.12= 0.536sec.
End time= FTT*2= 1.071sec.
d) For Re= 200%*2166= 4332.
Re = rho*U-inlet*D/mu.
U-inlet = (4332*1.81x10^(-5)/1.225*0.04)
U-inlet = 1.6m/s.
Flow through time= Length of domain/Velocity.
FTT= 0.6/1.6= 0.375sec.
End time= FTT*2= 0.75sec.
Procedure:
- Cylinder of above mentioned dimensions is created.
- Set the external flow analysis in the wizard.
- Calculated end time is taken as total analysis time.
- Fluid as air is taken into consideration.
- Velocity in the X-direction is taken as calculated U-inlet.
- Set the Computational domain in X-direction as 0.6m.
- Run the Project and Finally get the Cutplots of Relative pressure and Velocity.
Result:
For Baseline:
Velocity Distribution over Cylinder for baseline case
Pressure Distribution over Cylinder for baseline case
Animations:
Velocity: https://www.youtube.com/watch?v=KaAAoQWXtvY
Pressure: https://www.youtube.com/watch?v=Prcq3GrYJw0
For Re=20%:
Velocity Distribution over Cylinder for Re=20%
Pressure Distribution over Cylinder for Re=20%
Animations:
Velocity: https://www.youtube.com/watch?v=iL8ERCTq5x0
Pressure: https://www.youtube.com/watch?v=O9JrNb4riDw
For re=40%:
Velocity Distribution over Cylinder for Re=40%
Pressure Distribution over Cylinder for Re=40%
Animations:
Velocity: https://www.youtube.com/watch?v=81pALwLlQAI
Pressure: https://www.youtube.com/watch?v=XkGM_VKNZ6k
For Re=100%:
Velocity Distribution over Cylinder for Re=100%
Pressure Distribution over Cylinder for Re=100%
Animations:
Velocity: https://www.youtube.com/watch?v=XZRNtDZ8Ltk
Pressure: https://www.youtube.com/watch?v=jHCfvKE0PNc
Observations:
- Inlet velocity in x direction increases with the increase in reynolds number, thus increasing the flow of air over the cylinder.
- The Relative pressure variation does not varry to a large extent for the reynolds numbers taken.
- It is observed that the high pressure is created on the surface facing the inlet velocity.
- The velocity variation in the above animations has different velocity profiles, when the velocity is larger the velocity profile is longer behind the cylinder surface and it is approximately zero nearer to the cylinder surface (surface which is not in contact with inlet velocity).For higher values of the velocity waves are created behind the cylinder.