Week 2 - Flow over a Cylinder.

Aim:

To simulate the flow over a cylinder and explain the phenomenon of Karman vortex street.

Objective:

1. Calculate the coefficient of drag and lift over a cylinder by setting the Reynolds number to 10, 100, 1000, 10000, and 100000. (Run with a steady solver.)

2. Simulate the flow with the steady and unsteady cases and calculate the stochastic number for Re = 100.

Introduction:

Reynolds Number (Re):

The Reynolds number for a flow is a measure of the ratio of inertial to viscous forces in the flow of a fluid around a body.

Re = rho*V*d/Dynamic Viscosity

Vortex shadding:

Vortex shedding is an oscillating flow that takes place when a fluid such as air or water flows past a bluff (as opposed to streamlined) body at certain velocities, depending on the size and shape of the body. In this flow, vortices are created at the back of the body and detach periodically from either side of the body, forming a Von Karman vortex street. The fluid flow past the object creates alternating low-pressure vortices on the downstream side of the object. The object will tend to move towards the low-pressure zone.

Strouhal number (St):

A stochastic number is a dimensionless number describing oscillating flow mechanisms.

The Strouhal number is often given as

St = f*d/u

Where,

f is the frequency of vortex shading.

L is the characteristic length, and

U is the flow velocity.

Procedure

To get the desirable results we go through 3 major steps in the same sequel and based on the steps we followed during whole setup we got the results.

1. First of all, open the workbench
2. Drag the Fluid Flow (fluent) part in the Project schematic window
3. So, via going through Geometry option open the Space claim
4. Go to the open – new – go to geometry location – select open command
5. By following step 4 we will able to open the geometry in the space claim
6. Now choose the required volume from the whole geometry to do further process efficiently.
7. Check for any overlaps and the intersections that cause problem in the meshing.
8. After verifying the model and then close the window.
9. Now open Ansys Meshing and let the geometry upload.
10. Then firstly name all the parts of the model.
11. Then from the Tree right click on mesh and tap "Generate mesh"
12. Set the sizing of the meshing from its detail and then repeat the step 11.
13. After verifying the mesh, close the Ansys Meshing window.
14. Now open Ansys fluent window by clicking over ‘Setup’ and let the geometry upload.
15. For verifying the check click of ‘Checks’ option and see the results in console.
16. Go to the General and set the case accordingly as mentioned in the challenge
17. As we are dealing with temperature so mark the Energy option and chose the viscous flow option to define the fluid flow.
18. After this set the Boundary conditions.
19. Generated the graphs that we want to observe during the case run.
20. With this go to the results and create a plan in from the centre of the body and allow to show the velocity contour pattern over it during the case run time.
21. In addition to this, from ‘solving’ section also select animation for the same velocity contour.
22. The initialize the case
23. Set the total no. of iteration.
24. Click calculate to make simulation run
25. As the simulation completed close the tab and do the postprocessing as analyse the contours and plots.
26. For this select the plane slice that is situated in the centre of the geometry and over it we have to perform the contour analysis.
27. Close the tab after extracting useful results.
28. Save the case and cut the software.

Results:

Results are attached in the word file below.

Thanks

Anubhav