Flow around a (volley)ball (II) at medium Reynolds number

Flow around a (volley)ball in a channel at medium Reynolds number (see the Computational details). The aim of this study by students was to demonstrate the influence of the rotation of a volleyball with respect to different techniques of service. The values to be controlled were the drag and lift forces which mainly determine the length and speed of a service, and the difficulty for the contrary player to control the service ("flatter service").

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 "come down sooner"), and the drag forces increase! For a comparison, see the corresponding results for the higher Reynolds number configuration. It might be interesting to perform the same tests for an even more realistic Reynolds number, without a channel configuration, and to examine the effect of additional 3D effets. So, this pre-study is only a first attempt in applying the FEATFLOW software in sports sciences, with qualitative results only, but more realistic simulations should and can be performed!

• Distribution of temperature/concentration via Boussinesq model
  
  

  Visualization via tracing of concentration, starting from the inlet. Each row contains the videos for a zoomed representation with two different color maps (all about 1.1 MB, resp., 1.5 MB), and the video for the complete domain (about 0.9 MB each). The first row is for rotational speed 0 (no rotation), then followed by 0.1 (second), 1 (third) and finally for rotational speed 5 (fourth row).
  

  
  

  
  

  
  

  
  
  

• Pressure
  
  

  Visualization via pressure plots, shaded (first column, about 1.1 MB each) and via isolines (second column, about 8 MB). The rows correspond again to the different rotational speeds.
  

  
  

  
  

  
  

  
  
  

• Streamfunction
  
  

  Visualization via streamline plots, shaded (first column, about 1.2 MB each) and via isolines (second column, about 10 MB). The rows correspond again to the different rotational speeds.
  

  
  

  
  

  
  

  
  
  

• Velocity
  
  

  Visualization via vector plots (vectors, each about 8 MB).