Flow over a cylinder

Aim: To
• Run a Baseline simulation and calculate Reynolds number.
•Run transient flow simulations for each case of increase in Reynolds number by factore of 20%, 40% and 100% .
•Create Animations for Pressure Velocity for all the cases.

Theory:
Boundary Layer Separation:
For a external flow over a body, the detachment of a boundary layer from the surface of body is known as Boundary layer separation. Boundary layer may be laminar, transition or turbulent and its thickness goes on increasing in direction of flow.
Separation Point: The point on the profile at which the boundary layer seperates is Seperation Point.
Vortex Shedding:The boundary layer seperates from the surface and forms a shear layer which is highly unstable. This layer rolls into a discrete vortex and detaches from surface and this phenomenon called as Vortex Shedding.
Discrete Frequency given by
Strouhal Number: St=fD/v
St=0.21 for Reynolds number greater than 1000.

Procedure:
For a Baseline case,
diameter of cylinder,d=0.04m
Length of cylinder, L=0.04m
Velocity, v=1 m/s
For Air as fluid,
Density, =1.225 kg/m³
Dynamic Viscosity, =18.6×10^-6 uPa.s

Re=ρ v d/μ

where ρ= density of fluid

v= velocity of fluid

d=diameter of body

μ=dynamic viscosity of fluid

Re= (1.225 x 1 x 0.04)/18.6×10^-6

Re =2634.4086

Now lets calculate Reynolds number and Velocities for increase in baseline Re by 20%,40%and 100% respectively.
1) 20 % rise
Re=Re+20%Re

=2634.40+0.2(2634.40)
=3,161.29

Now, v=Re.μ/ρ.d

v=(3161.29 × 18.6 ×10^-6) /(1.225×0.04)
v= 1.19 m/s

2)40% rise
Re=3688.16
v=1.39 m/s

3) 100% rise
Re=5268.8
v=1.99m/s

Now we will model a cylinder and save it.Then we will setup a Flow Simulation using the wizard to choose a suitable computational domain. Then we will setup flow simulation for baseline.

Conclusion: With the increase in Reynolds number it can be seen that the Seperation point shifts forward along the cylinder which leads to lesser wake region.Hence more turbulent flow is preferable to reduce drag effect.

below i shall attach the necessary pictures and links.