PHYSICS 142/242

Spring 2009


Lecture 15:

Fluid Mechanics and Baseball Physics (PDF Document)


Flow around balls, circles, cylinders, etc.

The following examples show flows through channels, around a set of obstacles, as for instance circles and balls.



Right after the obstacle(s), the flow separates and produces complex flow patterns, oscillating in space and time. In many applications, the corresponding drag and lift forces acting on the obstacle(s) are of major interest, and a difficult numerical job to do! The complexity of the problem depends on the:

Short description


Flow around a (volley)ball in a channel at medium Reynolds number. The aim of this study by students is to demonstrate the influence of the rotation of a volleyball. The values to be controlled were the drag and lift forces which mainly determine the length and speed of a service, and the difficulty of return.

The following diagrams show the resulting drag and lift coefficients in time. While the speed of the (volley)ball was assumed to be 1.5, the rotational speeds were 0 (no rotation!), 0.1, 1 and 5. While the first three configurations (rotation speed less or almost equal the speed of the ball) are very similar, the fourth leads to non-comparable results.






As can be seen, the additional rotation leads to more negative lift coefficients (that means the ball will "break sooner"), and the drag forces increase!For a comparison, see the corresponding results for the higher Reynolds number configuration. It might be interesting to make the same tests for a even more realistic Reynolds number, without a channel configuration, and to examine the effect of additional 3D effets.




Description of the flow problem






Description of the spatial discretization






Description of the temporal discretization








Visualization