ABSTRACT
A cricket ball is said to swing when it moves in a plane that is perpendicular to the vertical plane of projection. Cricketers have observed this phenomenon for at least 100 years yet even today, the conditions and techniques required to exploit swing effectively are still hotly debated by cricket practitioners. Studies have been performed in wind tunnels 1,2,4 , where force imbalances leading to swing have been demonstrated. Such experiments, however, are expensive, have large numbers of different variable parameters, and reveal little about the actual mechanisms of swing.
In this study the air flow patterns around a cricket ball were analysed by using Computational Fluid Dynamics (CFD) software (FLOTRAN). An isothermal, incompressible, Newtonian fluid model was used throughout. Techniques based on aerofoil analysis were used to investigate the effect of Reynolds number and the angle of incidence of the seam at delivery. Initially an idealised 2D model (infinite cylinder representation) was used. Both steady-state (turbulent) and transient (laminar) flow solutions were obtained. Then using this experience, 3D spherical models were developed.
Visualisation of the flow patterns was achieved by colour coded contour maps. Pressure differences between the two sides of the ball were identified and were accompanied by asymmetric boundary layer separation. Transient solutions of velocity vectors and speed contours were animated to show asymmetric flow development and vortex shedding. The calculated lift and drag coefficients compared favourably with experimental data 2,4,2 . The topical phenomenon of ‘reverse swing’ was also observed.
CFD provides a detailed view of the airflow and turbulence around a cricket ball in flight. Despite the fact that these models need to be validated externally, they do shed light on the mechanisms of swing. Indeed this approach has the potential for analysing ‘form drag’ in other sports where speed and drag are intimately connected.
