Flow over a cylinder
Aim:
To simulate flow over a cylinder at different Reynolds numbers. 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.
Input parameters:
The Cylinder Dimension are as follows:-
Dia=0.02 m & Length=0.05 m ,Dynamic Viscosity of air @ 27 degree C=18.46*10^-6 Pas
Density of air=1.225 kg/m^3
Automatic Mesh with 4 levels of initial mesh & advance channel refinement is used.
Description:
Computational Fluid Dynamics:
Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows.
Reynolds number :
Reynolds number can reveal whether the flow is laminar or turbulent. The transition from laminar to turbulent flow depends on the surface roughness, flow velocity, geometry, surface temperature, and type of fluid, among others.
Where,
R = Reynolds Number
ρ = Fluid(Air) Density
v = Velocity of Fluid(Air)
D = Diameter of Cylinder
μ = Dynamic Viscosity of Fluid(Air)
Mesh generated cylinder:
calculation:
a) Baseline is 100%
Re = rho*U-inlet*D/mu= 2166.
D = cylinder dia= 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)When Reynolds number increased by 120%
Re= 120%*2166= 2600.
Re = rho*U-inlet*D/mu.
U-inlet = (2600*1.81x10^(-5)/1.225*0.04) = 0.96m/s.
Flow-through time= Length of domain/Velocity= 0.6/0.96= 0.625sec.
End time= FTT*2= 1.25sec.
c)When Reynolds number increased by 140%
Re= 140%*2166= 3032.
Re = rho*U-inlet*D/mu.
U-inlet = (3032*1.81x10^(-5)/1.225*0.04) = 1.12m/s.
Flow-through time= Length of domain/Velocity= 0.6/1.12= 0.536sec.
End time= FTT*2= 1.071sec.
d)When Reynolds number increased by 200%
Re= 200%*2166= 4332.
Re = rho*U-inlet*D/mu.
U-inlet = (4332*1.81x10^(-5)/1.225*0.04)= 1.6m/s.
Flow-through time= Length of domain/Velocity= 0.6/1.6= 0.375sec
End time= FTT*2= 0.75seccase 1:
It is the baseline where the Reynolds number is at 100%
Velocity:
Video:
https://drive.google.com/file/d/1wT6lZicko0Pdotee_xF3Kjah4nYfUAkH/view?usp=sharing
pressure:
video:
https://drive.google.com/file/d/1y0epzBrh8H43FMpnPb_KQuKJo47kADzH/view?usp=sharing
case 2:
when the Reynolds number is at 120%
Velocity:
Video:
https://drive.google.com/file/d/1sanE-ij-v40dGKj5NM9aVP9g1HhbgqaE/view?usp=sharing
pressure:
video:
https://drive.google.com/file/d/1_92nEPmsgH1G6KLLpEjAGN1SVhzLPpTf/view?usp=sharing
case 3:
when the Reynolds number is at 140%
Velocity:
Video:
https://drive.google.com/file/d/1k5cMKG8o5_IKTt7tOsseQjjlt-fLBZAT/view?usp=sharing
pressure:
video:
https://drive.google.com/file/d/16N2N5sxsu_HRuXG1gek4EJnSaDZ7ZbQv/view?usp=sharing
case 4:
when the Reynolds number is at 200%
Velocity:
Video:
https://drive.google.com/file/d/1jdBLnuk_i2wo9hYsm1pBpOYVaJrRASuO/view?usp=sharing
pressure:
video:
https://drive.google.com/file/d/1CQlxLwKR3qijeCj7Mp7ViAQyWKXSNSuD/view?usp=sharing
Result:
As we increase the Reynold's Number, the velocity of the external flow of air increases. And, time required to obtain a steady velocity & pressure profile decreases. As we increase the Reynold's Number, steadiness of velocity lines decreases & steadiness of pressure lines increases.