The surface of the golf ball is deliberately dented. The shape of a golf ball is one of the results of aerodynamic research. This is related to the turbulent transition and separation flow phenomenon of the flow around the sphere (that is, the flow around the sphere).
Smooth sphere around the flow, turbulence transition occurs late, and turbulence corresponding to the regular flow called laminar flow. The laminar boundary layer is more prone to flow separation phenomenon (that is, the streamline leaves the surface of the ball), the head of the sphere to form a high pressure area, the back to form a large low pressure area, resulting in great resistance (pressure difference resistance). Make the golf ball fly very little distance.
When the surface of the sphere has a dent, the dent promotes turbulent transition, turbulent boundary layer is not easy to occur flow separation phenomenon, so that the low pressure area behind the sphere is small, reduce the resistance. Make the golf ball fly the distance increased.
The friction of turbulent flow is larger than that of laminar flow, but it plays a small role compared with the shape resistance, so the total drag is smaller.
The small protrusion of the surface of the golf ball can also play a role in promoting the separation, but the interference of the protrusion on the flow is some difficult to control, causing some lateral force (also called lift).
There is no lift around a sphere. The rotation creates lift. A proper lift-drag ratio will increase the flight range. Different directions of rotation can create a "banana ball" effect.
In addition, the rules of golf state that a golf ball shall not be designed, manufactured, or intentionally altered to have characteristics other than the symmetry of a ball.
