Flow over a cylinder

Aim: To perform a flow simulation over a pipe.

Introduction & Basic Theory: The flow simulation is basically the study of flow of liquid over or in a surface. In our case we are going to use a pipe and we are going to see the basic air flow over it. We will create a cylindrical pipe and using air as fluid we will run our simulation. These simulations allows us to study the fluid behaviour over the surface of the object and helps us understand the restrictions offered by the object to the fluid flow. By running this simulation we can see the velocity changes along the pipe surface.

Case Setup/Reprt:

1. Firstly we will generate a cad model of the cylindrical pipe as shown in the video; i.e. of dia 0.02 m and a length of 0.05 m
2. Then after saving the file we will go to flow simulation and click on the Wizaed option to set the flow simulation
3. We have to make sure that we select the external setup as we have to do a flow simulation over the surface of the pipe
4. Then after setting the units and the assigning the fluid (which is air in our case) we can go further to specify the velociity in the X direction as 10 m/s and then selecting the time limit for the simulations to work
5. Further after we can hit the run button and the calculations starts
6. Then to see the plot we can use the use the cut section option to generate a cut plane to analyse the results
7. We can run the calculations for finner meshes to get a more sophisticated plot
8. We can use the formula to calculate the renaults number for this case. The formula for the same is shown below in the calculation section
9. further after getting the Reynold's number we will increse it for a percentage of 20%, 40% and 100% and run the simulation again to study the flow behaviour
10. Also we will annimate the flow sequence so that we can see the flow of air over the pipe

Formula & Calculations:

`Reynold's Number=(Velocity*Desnsity*Diameter)/(Viscocity)`

Thus in our case the

Diameter is 0.02 m

Velocity is 10 m/s

Density is 1.225 kg/m^3

Viscocity is 1.81*10^-5 Pa-s

Thus using these values the Reynold's Number comes out to be 13535.9 which is approximately 13536

The output for this case can be seen below:

For a mesh of 3 in solidworks:

For the velocity plot:

The animation for this study can be seen as:

For a finer mesh the results are as:

The annimations can bbe seen as :

The Pressure Curve for the same is as:

For a mesh size of 3:

And the annimation of the same can be seen as:

For the same setup we will see the pressure flow for a mesh size of 7:

The aannimated video for the fressure flow is as:

Thus from the results we can see that the numerical value of the simulation is same, its just that because of the creation of the finer mesh we can see that the graphical representation is more clear and the flow behaviour can be read more easily.

The air when colides with the cylindrical surfaces the molecules colides with the surface and along each other thus increasing the velocity around the start of the collision point and the area in front of the cylinder acts as a low pressure area thus the velocity is low there. Also as the air particles find it tough to excase from the center part of the crlinder while flowing from left to right hence the pressure is more on the left side along the radial point from the center.

Also with the more finer mesh the result computation takes more time to be executed. Thus for the further cases we will run simulation for a mesh grid of 4.

Thus for Further calculations we are going to increase the Reynolds number by 20%, 40% and 100%

Case 1:

For a 20% increase in Reynolds number

Thus the new Renaulds number turns out to be 16243.2

Now for this setup the velocity turns out to be 12 m/s

Thus in this case we will add the input value as 12 m/s for the earlier 10 m/s and we will run the simulation again

The results for this setup can be seen below:

The Velocity plot can be seen as:

The annimated video of the same can be seen below:

The pressure plot for the same setup is as:

The animated behaviour for the same can be seen below:

Thus from the plot we can see that as the inlet velocity increases the velocity around the collission area also increases. Also the pressure at the center point around the cylinder on the flow side also increases.

Case 2:

For a 40% increase in Reynolds number

Thus the new Renaulds number turns out to be 18950.6

Now for this setup the velocity turns out to be 14 m/s

Thus in this case we will add the input value as 14 m/s for the earlier 12 m/s and we will run the simulation again

The results for this setup can be seen below:

The Velocity Plot:

The annimation of the same can be seen below:

The Pressure Plot:

The annimation of the same can be seen below:

Case 3:

For a 100% increase in Reynolds number

Thus the new Renaulds number turns out to be 27072. As the Reynold's number is greater than 25000 thus this is going to be a turbulant flow.

Now for this setup the velocity turns out to be 20 m/s

Thus in this case we will add the input value as 20 m/s for the earlier 14 m/s and we will run the simulation again

This being a turbulant flow we will run the simulation two times for a mesh size of 4 and 7 both to see the difference in the flow plot or pattern.

The results for the mesh size of 4 setup can be seen below:

The velocity plot can be seen below:

The animation for the same can be seen below:

The Pressure plot for the same can be seen as:

And the annimation for the same can be seen below:

Now, we will run the simulation for the mesh size of 7 and see the results.

The velocity plot can be seen as:

The annimated video of the same can be seen below:

Now the pressure plot for this can be seen as:

The annimated video for the same can be seen below:

Conclusion:

From the above plots and animations we can see that as the velocity increases there is an increse in push out force and the distribution along the curcumference of the pipe near the collision side increses. The case is also same for the pressure plot.

The nature of the plot and graph is same in all the cases its just that with the increse in the input valve the output valve also increases.