Numerical investigation of the flow over a golf ball in the subcritical and supercritical regimes

Numerical Investigation of the Flow Around a Golf Ball at Around the Critical Reynolds Number and its Comparison with a Smooth Sphere

“…The shear layers developed following the local separation on the leading edge of the dimples quickly become unstable and small-scale vortices are generated within the dimples. Similar local separation characteristics were also reported by Choi et al [2] and Smith et al [3]. The unstable flow behavior results in a momentum increase of the near-wall flow and the consequent local reattachment inside the golf ball dimples.…”

“…In particular, triangular elements are generated on the golf ball surface for properly reproducing the dimple details, and prism layers are allocated along the normal-wall direction starting from the surface mesh. To accurately capture the boundary layer separation and turbulence transition, the numerical grid around the golf ball must be of sufficient resolution [3,10]. In the present study, the surface mesh size on the dimple edges is set to be approximately 2.34× 10 −3 D. There are about 40 triangular elements across the dimples and about 28 prism layers being generated within the distance of dimple depth k. The total cell number amounts to around 145 million.…”

“…One can clearly observe that the drag coefficient of the golf ball at Re=1.7× 10 5 has already reduced by nearly 50 % when compared to the smooth sphere case conducted by Muto et al [10] at a similar Reynolds number (Re=1.6× 10 5 ). In particular, the dimensionless parameter k/D of the golf ball is considered as one of the essential factors affecting the supercritical drag coefficient and the critical Reynolds number range in which the drag crisis occurs [1][2][3]. Actually, the golf ball used in the present study has the relative dimple depth (k/D=0.5× 10 −2 ) very close to that of Choi's [2] golf ball model (k/D=0.4× 10 −2 ), but much smaller than that of Bearman's [1] golf ball model (k/D=0.9× 10 −2 ).…”

“…Previous studies [1][2][3] have revealed that the dimples on a golf ball could lead to the drag crisis at Reynolds numbers remarkably lower than the typical critical Reynolds number of smooth sphere cases [4]. Interestingly, such lower Reynolds numbers are in the range where most golf tournaments are played [5].…”

“…Due to the challenges of computing the flow past golf balls [12], the mechanism proposed by Choi et al has not been numerically demonstrated until very recently. Smith et al [3] conducted direct numerical simulations (DNS) for the flow over a stationary golf ball at the subcritical and supercritical Reynolds numbers. Their calculation results further solidified the process of the local separation and local reattachment.…”