ゴルフボールディンプルによる乱れの発達過程とエネルギー輸送について

抄録

We prepared the computational domain, which 9 dimples of golf ball are linearly distributed on a flat plane. The Reynolds number based on dimple diameter is 22000 and a time step is 1×10^-5s. We found out that the momentum thickness on a first dimple was also same value for different depth models and the momentum of the flow over 9 dimples didn’t change significantly after a fourth dimple. We think turbulence doesn’t develop after the fourth dimple. Observing the vortex structure visualized by lamda2-criterion (λ²=-6×10⁸ /s²), there was no vortex on first dimple. Span axis vortices was generated on second dimple and it transformed to hairpin and streamwise vortices. After third dimple, there are almost only streamwise vortices except around dimple edges. These vortices help to transport a momentum from main flow to a turbulent boundary layer. Then, we measured vorticities for each directions ω_x, ω_y, ω_z. The maximal value of ω_x didn’t change after the fourth dimple, so that the momentum hardly change. As these results, we revealed that the vortex structure is completed over there dimples.