Abstract
Large-eddy simulations are conducted for a rotating golf ball and a rotating smooth sphere at a constant rotational speed at the subcritical, critical and supercritical Reynolds numbers. A negative lift force is generated in the critical regime for both models, whereas positive lift forces are generated in the subcritical and supercritical regimes. Detailed analysis on the flow separations on different sides of the models reveals the mechanism of the negative Magnus effect. Further investigation of the unsteady aerodynamics reveals the effect of rotating motion on the development of lateral forces and wake flow structures. It is found that the rotating motion helps to stabilize the resultant lateral forces for both models especially in the supercritical regime.
Highlights
Golf ball dimples have been discovered to be generally efficient in promoting the drag crisis phenomenon [1,2,3], i.e. the drag drops at a lower critical Reynolds number for a golf ball when compared to a smooth sphere
The aerodynamic forces exerted on the golf balls were measured over a wide range of Reynolds number and spin parameter using the wind tunnel technique developed in their study, and the results reveal three important phenomena: (1) the golf ball dimples causes the drag force reduction at a lower Reynolds number when compared to a smooth sphere
It is remarkable that a negative lift force was obtained for both rotating models at the critical Reynolds numbers with current spin parameter ( = 0.1) while positive lift forces were generated for both models at the subcritical and supercritical Reynolds numbers
Summary
Golf ball dimples have been discovered to be generally efficient in promoting the drag crisis phenomenon [1,2,3], i.e. the drag drops at a lower critical Reynolds number for a golf ball when compared to a smooth sphere. Beratlis et al [7] extended the work of Smith et al [3] to the investigation of flow past rotating golf balls They conducted the direct numerical simulations of the rotating golf ball with the same spin parameter at four different Reynolds numbers spanning from the subcritical regime to the supercritical regime. Based on the measurements of the time-averaged tangential velocities on both sides of the golf ball, Beratlis et al suggested that the flow separation on the side spinning against the main flow was delayed due to its local instability, which directly contributed to the generation of the negative lift force This conclusion is analogous to the assumption by Bearman and Harvey [1]. The ordinary and negative Magnus effect on the spinning golf ball are investigated, and the unsteady aerodynamics of the spinning golf ball is discussed in detail
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