TO TRANSIENT FLOW SIMULATION OVER A CYLINDER BY USING SOLIDWORKS
AIM :
To run the transient external flow simulation over a cylinder by using an solidworks flow simulation.
FLOW OF CONTENT/METHODOLOGY :
OBJECTIVE :
1) Calculate the baseline reynolds number by use this value to integrate factor of 1.20 , 1.40 & 2.00.
2) Find out the flow simulation end time by using velocity formula and increase it two times.
3) Create a plot and flow animation of pressure & velocity.
INTRODUCTION :
Computational fluid dynamics is a science that, with the help of digital computers, produces quantitative predictions of a flow phenomena based on Navier stroke equation is consists of conservation laws such as time dependent continuity equation for conservation of mass, three time dependent conservation of momentum equation and a time dependent conservation of energy equation.
External flow over a surface :
In fluid mechanics, external flow is such a flow that boundary layer develops freely, without constraints imposed by adjacent surfaces. Accordindly, there will always exist a region of the flow outside the boundary layer in which velocity, temperature and concentration gradients are negligible. It can be defined as the flow of a fluid around a body that is completely submerged in it.
Vortex shedding for external flow over body :
The vortex shedding forms behind a circular cylinder. In fluid dynamics, vortex shedding ia an oscillating flow that takes place when a fluid such as air flows past or bluff body at certain velocities, depending on size and shape of the body. The fluid flow past the object creates alternating low pressure vortices on the downstream side of the object. The object will try tend to move toward the low pressure zone.
Reynold's Number
It is defined as the ratio of inertia force of a flowing fluid and the viscous force of the fluid. The expression for reynold's number is obtained as
Reynold's Number,`Re = (rhotimesvtimesD)/mu`
= `(v*D)/nu` `because mu/rho = nu`
Where,
`rho =`density (kg/m^3)
v = Velocity (m/sec)
D = Diameter of pipe (m)
`nu =` Kinematic viscosity (m^2/sec)
`mu =`Dynamic viscosity (Ns/m^2)
ANALYTICAL CALCULATION :
Assumed values
Temperature = 298 K
Density = 1.1649 kg/m^3
Dynamic viscosity = 1.8680*10^-5 kg/m.s
Kinematic viscosity = 1.6036*10^-5 m^2/s
Case details with tabulation
Inlet velocity = 10
Baseline reynolds Number = 124712.16
| Case | Increasing factor of baseline reynolds number | Reynolds number | Velocity, m/sec | Domain length, m | Fluid flow end time, Seconds | Time taken for per one result, Seconds |
| 1 | 1.00 | 124712.16 | 10 | 0.200 | 0.040 | 0.0040 |
| 2 | 1.20 | 14966.59 | 12 | 0.200 | 0.0332 | 0.00332 |
| 3 | 1.40 | 17461.024 | 14 | 0.200 | 0.028 | 0.0028 |
| 4 | 2.00 | 24944.32 | 20 | 0.200 | 0.022 | 0.002 |
CREATE A MODEL AND FLUID FLOW DOMAIN :
Create a cylinder
Create a circle and extrude it with appropriate dimensions. After that, we get the cylinder for which fluid flow analysis. See fig (i)
Diameter of the cylinder = 0.02 m
Length of the cylinder = 0.05 m
Fig (i)
Wizard initial and ambient condition
Unit system : SI
Flow type : External flow
Working fluid : Air
Pressure : 101325 Pascals
Temperature : 293 K
Velocity in X direction : 10 m/s (for case 1)
Air passing over the selected surface of the cylinder on X direction, Zero velocity in Y & Z direction. See fig(ii)
Fig (ii)
DISCRITIZATION OF DOMAIN :
The process of discritize the mathematical domain is dividing into finite element is called meshing. In computational fluid dynamics discritize method is finite volume method and type of element is hexahedral.
Refining the mesh in 3 times around the selected surface at fig (ii)
Near the selected surface element is 3 times refined from previous element, the element type is hexahedral.
INITIAL AND BOUNDARY CONDITION :
Initially, we assume the velocity of air flows in X direction calculate from the baseline reynolds number, Similarly remaining cases as well. The fluid flows direction is positive direction on x coordinate.
The analysis type is external flow and end time flow is 0.04 seconds with 10 steps.The displacement from inlet to outlet is 0.200 meter. These are only case 1, similarly we did for remaining three cases.
POST PROCESSING :
CASE 1
Velocity contour plot for case 1
The inlet velocity of air flow is 10 m/s in this case. The air is striked on the cylinder, velocity is reduced drastically at the center of the cylinder due to obstacle and pressure is increased drastically at that particular point. The fluid flows over the cylinder, velocity is increased and vortex shedding is created on object downstream region. Behind the body or object velocity is close to zero and very low pressure is alive. Over the fluid flow in the domain, the velocity is less than the inlet velocity on the downstream region of the body. The legend shows the maximum and minimum velocity in our domain.
The velocity is high when the air flows over the cylinder.
You tube link for Velocity contour animation for case 1 : https://www.youtube.com/watch?v=m-U6wR3n9c4
Pressure contour plot for case 1
Air is striked on the cylinder, the velocity is reduced drastically and pressure increased. The pressure and velocity is inversely proportional on the particular striking region. Because, behind the cylinder the pressure and velocity is low from legend observation.
Atmospheric pressure is a reference pressure for finding the absolute pressure. When the pressure is higher than the atmospheric pressure, it is a high pressure is created. When the pressure is lower than the atmospheric pressure, it's called Vacuum pressure.
You tube link for pressure contour animation for case 1 : https://www.youtube.com/watch?v=5HmLYStHCM0
CASE 2
Velocity contour plot for case 2
You tube link for velocity contour animation for case 2 : https://www.youtube.com/watch?v=EZPfmlOZY9c
Pressure contour plot for case 2
You tube link for pressure contour animation for case 2 : https://www.youtube.com/watch?v=5HmLYStHCM0
CASE 3
Velocity contour plot for case 3
You tube link for velocity contour animation for case 3 : https://www.youtube.com/watch?v=wSHmRRD-4aI
Pressure contour plot for case 3
You tube link for pressure contour animation for case 3 : https://www.youtube.com/watch?v=EWKQ_IQ2nQI
CASE 4
Velocity contour plot for case 4
You tube link for velocity contour animation for case 4 : https://www.youtube.com/watch?v=QC9Xxtg8Nmo
Pressure contour plot for case 4
You tube link for pressure contour animation for case 4 : https://www.youtube.com/watch?v=qGVx7DRgKI8
OBSERVATIONS :
1) The reynolds number is directly proportional to velocity, it satisfied from all cases. All the cases are converged from 59 to 62 iterations.
2) All pressure contour are looks like same. But we closely observe the legend pressure had been increased for each cases from one to fourth.
3) Similarly, all velocity contour are looks like same. But we closely observe the legend pressure had been increased for each cases from one to fourth.
4) Vortex shedding was happens for all the conditions from velocity contour.
5) Fluid flow end time from inlet to outlet is reduced, when the reynolds number is increased.
6) Density is increased at the time air gets striked in front of the cylinder in fluid flow direction.
CONCLUSION :
Finally, to run the flow over the cylinder for which different reynolds number. Moreover, to post processing or extracted useful data for numerical model of a flow animations for pressure and velocity contours.
REFERANCE :
1) https://theengineeringmindset.com/properties-of-air-at-atmospheric-pressure/