Simulating flow over a cylinder using SolidWorks
AIM
To simulate the flow over a cylinder.
THEORY
Reynolds number, Re = `(rho*V*l)/mu` = `(V*l)/nu` , where
`rho` = density of the fluid (kg/`m^3`)
V = velocity of the fluid (m/s)
l = characteristic length of the fluid (m)
`mu` = dynamic viscosity (`Pa*s`)
`nu` = kinematic viscosity (`m^2`/s)
THEORY
Reynolds number is a dimensionless quantity. It is the ratio of the inertial forces to the viscous forces within a fluid. Reynolds number quantifies the relative importance of these forces over each other and helps in determining the type of flow under given conditions.
Flow simulation
It allows prediction and analysis of how a fluid (liquid or gases) might be impacted by complex geometries or varying conditions in an operational environment. It is helpful in determining the behaviour of system under various and extreme circumstances.
OBJECTIVE
The objective here is to simulate the flow of any fluid (in this case, air) over a cylinder and then generate the cut plots for velocity and pressure. Then, an animation is made to describe the variation of velocity and pressure profile with time. We would be considering several cases, starting with a baseline condition and calculating the Reynolds number for the inputs provided. for subsequent cases, the Reynolds number would be increased by a factor of 20%, 40% and 100% and the analysis would be done.
The initial conditions are set to 293.2K temperature and 101325 Pa pressure. The velocity is provided in the X-direction for the flow to take place. The end time for the flow is also provided.
For these simulations, we create a cylinder having diameter of 40mm and length 60mm.
(mesh and computational domain)
End time for the simulation
In order to perform the simulation, its end time needs to be determined. We know that `speed = (dis ta nce)/(time)`
In this case, distance is the length of domain in the X-direction. Length of domain for a cylinder of diameter 40mm is equal to 0.22 + 0.14 = 0.36m = distance between YZ planes of the computational domain.
Speed = velocity of flow provided and
time is the flow through time.
Now, end time is taken as twice of the flow through time, that is, end time = 2*flow through time.
Baseline simulation parameters
| Initial velocity | 1 m/s |
| Reynolds number | 2657.8 |
End time = 2*`0.36/1` = 0.72 sec
VELOCITY SIMULATION
https://drive.google.com/file/d/1xm56ukkAOwnyecOPJHOrYpjr3yj4BVWt/view?usp=sharing
PRESSURE SIMULATION
https://drive.google.com/file/d/1Oa0xwpMiY5ixfDngm55z8dXJqpKXIuAp/view?usp=sharing
Reynolds number increased by 20%
| Initial velocity | 1.2 m/s |
| Reynolds number | 3189.37 |
End time = 2*`0.36/1.2` = 0.6 sec
VELOCITY SIMULATION
https://drive.google.com/file/d/1B8NIJrqLPNehKxMsgRq2_v0BtqhGRvQd/view?usp=sharing
PRESSURE SIMULATION
https://drive.google.com/file/d/1Nlz652Nt5ilH4MqjARBoHhnfMsdKYois/view?usp=sharing
Reynolds number increased by 40%
| Initial velocity | 1.4 m/s |
| Reynolds number | 3780.93 |
End time = 2*`0.36/1.4` = 0.52 sec (approx)
VELOCITY SIMULATION
https://drive.google.com/file/d/136b71T0drOETcNtJovdWBZE0jKMYAtPW/view?usp=sharing
PRESSURE SIMULATION
https://drive.google.com/file/d/1JlvU6PXNXdpEv7wpB2J4SNIpauC8Pm2s/view?usp=sharing
Reynolds number increased by 100%
| Initial velocity | 2 m/s |
| Reynolds number | 5315.62 |
End time = 2*`0.36/2` = 0.36 sec
VELOCITY SIMULATION
https://drive.google.com/file/d/11eUxLZisq1vE53If1HcXm2vqzgUaA0O1/view?usp=sharing
PRESSURE SIMULATION
https://drive.google.com/file/d/1vK2yWjQ0LMlhpWvewAEO3jg3fQBQScu3/view?usp=sharing
OBSERVATION AND CONSCLUSION
The velocity increases with same proportion as the Reynolds number as the other parameters are constant.
There is no significant variation in the pressure plot because pressure is dependent on area which remains the same. Also, pressure is maximum at the rear face of the cylinder, which is the point of impact of the flow with the cylinder.
The velocity is approximately zero near the surface, at the side not in contact with the inlet flow. For larger values of Reynolds number (larger inlet velocity), velocity profile is longer behind the cylinder, i.e, on the side facing the flow.