The technique of swing bowling is used in the sport of cricket to gain an advantage over the batter, and improve a team’s chance of winning a match. The current best practice for swing bowling is based on anecdotal evidence, with little consensus on the optimal strategies. Bowling technique, the condition of the ball and atmospheric conditions are all considered important for swing, yet there is little quantification of these factors even in elite cricket. Previous experimental studies have not provided a description of swing that aligns with measurements of on-field swing made using ball-tracking technology.

This research looks to provide clarity on the physical mechanisms behind swing bowling for new and used cricket balls. Appropriate boundary conditions are measured in field tests, and applied to experiments so that results represent on-field swing. Wind tunnel tests are performed which measure the changes in the aerodynamic force coefficient, CF. The relevant findings are related back to cricket through tools for use in the professional game.

For new cricket balls, it is shown that conventional swing has a magnitude of 0.3 <C < 0.4, caused by the separation asymmetry between a laminar boundary layer and a reattached boundary layer. High Reynolds Number flow over 190,000, turbulence intensity above 0.6% and geometric features are all shown to inhibit conventional swing through non seam side boundary layer reattachment. This behaviour corresponds to low magnitude reverse swing, with a force coefficient of CF = −0.1. Rotational averaging is used to model rotating cricket balls, and produces a continuum of average force coefficients between these two values.

Surface roughness is shown to change the boundary layer state on used cricket balls, and is quantified using equivalent sand-grain roughness, ks, and roughness Reynolds Number, Rek. Conventional swing is maximised by creating a smooth surface on both sides of the ball, maintaining a force coefficient in the range 0.3 <CF < 0.4. Reverse swing is largest when the seam side has a fully turbulent boundary layer, with values of seam side roughness Reynolds Numbers over 65 producing reverse swing in the range −0.4 <CF < −0.3.

The output of a statistical model for new ball swing matches historic data to within 5% when predicting the number of deliveries with a certain force coefficient. The results indicate that the physics of new ball swing in this thesis are sufficient to describe professional cricket. This result allows the model to be used as a predictive tool for on-field swing.

Future work will look to implement the findings of this thesis to improve the performance of elite cricketers through continued work with coaches and analysts.