Flow over a cylinder
AIM: To Simulate the flow over a cylinder for different conditions.
OBJECTIVE:
- 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.
- Calculate stimulation end time.
- Create animations for pressure-velocity for all the three Reynolds number.
THEORY:
The Reynolds number (Re) is an important dimensionless quantity in fluid mechanics used to help predict flow patterns in different fluid flow situations. At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers turbulence results from differences in the fluid's speed and direction, which may sometimes intersect or even move counter to the overall direction of the flow (eddy currents). The Reynolds number has wide applications, ranging from liquid flow in a pipe to the passage of air over an aircraft wing.
The Reynolds number is defined as,
`R_e=(ρ*V*D )/μ`
Where,
- ρ is the density of the fluid (SI units: kg/m3)
- V is the velocity (m/s)
- D is the diameter of the tube (m)
- μ is the dynamic viscosity of the fluid (Pa·s or N·s/m2 or kg/(m·s))
INPUTS AND CALCUATIONS:
Diameter of pipe (D): 0.02m
Length of pipe: 0.05m
For AIR,
Dynamic viscosity (μ) = 1.802*10^ (-5) kg/(m·s)
Density (ρ) = 1.225 kg/m3
Putting all the values in Reynolds number formula we get,
Re = 1359.6*V
- Baseline condition
Initial velocity =10m/s
Length of domain =0.75 m
Time in sec = 0.075 sec
End time =2*0.075
= 0.15sec
Re= 1359.6*V
= 1359.6*10
= 13596
- For 20% increase
Re=16315.2
V=12 m/s
- For 40% increase
Re=19034.4
V=14 m/s
- For 100% increase
Re=27192
V=20 m/s
END TIME CALCULATION:
|
V |
L |
T= (L/V) |
End time = 2*T |
|
10 |
0.75 |
0.075 |
0.15 |
|
12 |
0.75 |
0.0625 |
0.125 |
|
14 |
0.75 |
0.0535 |
0.10714 |
|
20 |
0.75 |
0.0375 |
0.075 |
3D MODEL:
PROCEDURE:
- The first step was to prepare the cylinder of diameter 0.02m and length 0.05m.
- Then we open the flow stimulation wizard and select the required inputs, here in the wizard we select a time dependent stimulation where we input the calculated end time.
- Then we adjust the computational domain and give the input and output conditions.
- Then we run the stimulation and after the stimulation gets over we create cut plots for velocity and pressure.
- Then using the animation wizard we create the animation for the flow of velocity and pressure.
OUTPUTS:
CASE 1: For velocity = 10 m/s
Velocity Cut-plot:
Animation link:
https://drive.google.com/drive/u/2/folders/1iArLk1KXC6Ik3X8qYgJ6fduTkCzPcrsq
Pressure cut-plot:
Animation link:
https://drive.google.com/drive/u/2/folders/1iArLk1KXC6Ik3X8qYgJ6fduTkCzPcrsq
CASE 2: For velocity = 12 m/s
Velocity Cut-plot:
Animation link:
https://drive.google.com/drive/u/2/folders/1vBld2AcUTF56U2xttv1K75NmuDOTtC7O
Pressure cut-plot:
Animation link:
https://drive.google.com/drive/u/2/folders/1vBld2AcUTF56U2xttv1K75NmuDOTtC7O
CASE 3: For velocity = 14m/s
Velocity Cut-plot:
Animation link:
https://drive.google.com/drive/u/2/folders/1sFJALUc6yKzGDK5PsYnW65YFE4yzQBoJ
Pressure cut-plot:
Animation link:
https://drive.google.com/drive/u/2/folders/1sFJALUc6yKzGDK5PsYnW65YFE4yzQBoJ
CASE 4: For velocity = 20m/s
Velocity Cut-plot:
Animation link:
https://drive.google.com/drive/u/2/folders/1Km_ENkts371czXkGjE5jtHZvVusHXyRU
Pressure cut-plot:
Animation link:
https://drive.google.com/drive/u/2/folders/1Km_ENkts371czXkGjE5jtHZvVusHXyRU
CONCLUSION:
Since Reynolds number is directly proportional to velocity, with increase in Reynolds number the velocity of fluid also increases. As velocity increases the pressure also increases.
Drive link:
https://drive.google.com/drive/u/2/folders/1trWV2zqvybYnbiHHNInzG3CLFNr7I7G_