External Flow Over a Cylinder Using SolidWorks

Aim:

To run an External flow simulation Over a Cylinder using Solidworks with increase in the Reynolds number by a factor of 20%, 40%, and 100% at each case from its initial Value.

Objective:

1. To create a pipe of suitable dimension.
2. To Run a baseline simulation and then to calculate the Reynolds number.
3. Then to increase the Reynolds number by a factor of 20%, 40%, and 100%
4. And then to run the transient flow simulation.
5. To Create animations for pressure-velocity for all the three Reynolds numbers.
6. Finally to explain the observations.

Theory:

External flows past objects have been studied extensively because of their many practical applications.For example, airfoils are made into streamline shapes in order to increase the lifts, and at the same time, reducing the aerodynamic drags exerted on the wings.On the other hand, flow past a blunt body, such as a circular cylinder, usually experiences boundary layer separation and very strong flow oscillations in the wake region behind the body.

In certain Reynolds number range, a periodic flow motion will develop in the wake as a result of boundary layer vortices being shed alternatively from either side of the cylinder.This regular pattern of vortices in the wake is called a Karman vortex street. It creates an oscillating flow at a discrete frequency that is correlated to the Reynolds number of the flow. The periodic nature of the vortex shedding phenomenon can sometimes lead to unwanted structural vibrations, especially when the shedding frequency matches one of the resonant frequencies of the

Software Used:

Solidworks

Formula:

In order to obtain the Reynolds numbers for each case, The following formula is used

Diameter of Cylinder, D = 0.04 m

Length of Cylinder L = 0.05 m

dynamic viscosity of air, μ = 1.8205 Ns/m2

Fluid density, ρ = 1.2250 Kg/m3

Initial inlet velocity of 1m/s is chosen for simulation,

Therefore, Re =(1.2250*1*0.04 )/1.8205

Re =0.02691

Similarly for other cases using the formula,

Simulation end time is a little over 2 times the flow thorugh time as stated in the challenge.

Procedure:

1. First select the Flow Simulation Add-in in SolidWorks.
2. A cylinder of diameter 0.04 m and length 0.05 m was created in solidworks and then saved.
3. A new study was created using Flow Simulation Wizard.
4. In the wizard, External Flow was selected as the flow type as we are dealing with external flow over a cylinder.
5. Transient Study(Time Dependent) was selected and the study time was set to 5 seconds(as given in the challenge).
6. Air was selected as the working fluid of choice for the study.
7. Velocity of 1 m/s was given in X direction based on the model.
8. Two cutplots each for inlet velocity and pressure are inserted.
9. The animation is set up for the cut plots.
10. The process is repeated by increasing the Reynolds number by 20%,40% and 100% of the initial Reynolds number at each of the Cases.

Outputs & Animation:

From the table that is shown under the formula section,The velocities are setup and the corresponding pressure and velocity animations for each of the cases are diaplayed below,

1.Case (1)- Initially Velocity 1 m/s:

1.1.Cutplot animation for Pressure

https://youtu.be/ZTyA-8EQH2k

1.2.Cutplot animation for Velocity

https://youtu.be/VjzLeS-A7eM

2.Case (2)- Velocity 1.2 m/s (20% increase in Reynolds number):

2.1.Cutplot animation for Pressure

https://youtu.be/WgadblCoYbc

2.2.Cutplot animation for Velocity

https://youtu.be/hV5peOElCpo

3.Case (3)- Velocity 1.4 m/s (40% increase in Reynolds number):

3.1.Cutplot animation for Pressure

https://youtu.be/wndmH0oFlPU

3.2.Cutplot animation for Velocity

https://youtu.be/haGoWjIn1Mk

4.Case (4)- Velocity 2 m/s (100% increase in Reynolds number):

4.1.Cutplot animation for Pressure

https://youtu.be/xHf1_eCyx1g

4.2.Cutplot animation for Velocity

https://youtu.be/j6tkirc5clo

References:

1. http://www.eng.fsu.edu/~shih/succeed/cylinder/cylinder.htm
2. https://nptel.ac.in/content/storage2/courses/112104159/module2/Lec12.pdf

Conclusion:

1. Turbulent flow occurs at high values of Reynolds number and at high velocities and is dominated by inertia forces, which tend to produce chaotic eddies, vortices, and other flow instabilities.
2. Laminar flow occurs at low values of Reynolds numbers and at low velocities, where viscous forces are dominant, and is characterized by smooth, constant fluid motion.The above factors are clearly visible from the velocity animations but when it comes to pressure, there is hardly any change in all of the four animations.
3. Thus it could be concluded that Reynold's number is not playing a major part in the pressure distribution while on the other hand Reynolds number hugely influences the velocity distribution of the flow.