Why do golf balls with dimples fly further than balls without? In case you don’t know, here are the two main reasons:
- Dimpled surface reduces drag
- Dimpled surface improves lift
First, a quick lesson in Hydrodynamics (Aerodynamics).
There are two types of flow around an object: laminar and turbulent
Laminar flow has less drag and moves in smooth paths or layers around the object, but it is also prone to a phenomenon called "separation." Once separation of a laminar boundary layer occurs, drag dramatically increases because eddies form in the gap.
Turbulent flow has more drag initially but better adhesion, therefore is less prone to separation. If the shape of an object is such that separation occurs easily, it is better to have a turbulent boundary layer in order to increase adhesion to reduce eddies (which means a significant reduction in drag). Dimples on golf balls have the turbulent boundary layer.
3DFINS was a pioneer and tested these principles on surfboard fins.
With advanced Computer Flow Dynamic testing, 3DFINS compared two of the same size fins, one fin with dimples and the second without dimples. The test was conducted by flow dynamics expert Darrin Stephens (formally of CSIRO) and the results were surprising.
A surfboard fin with a smooth surface performs much like a golf ball with a smooth surface, it has a Lamina flow over the surface. This works well on surf fins at lower speeds and traveling straight, but when you reach higher speeds and start to turn, the fluid will start to separate from the foil or fins surface. This creates a separation bubble on the surface of the fin, which occurs when the fluid detaches from the surface of the fin, resulting in increased drag, reducing the lift and ultimately slowing of the fin.
The smooth surface fin also has known phenomena called “wingtip vortices”. This is a pressure imbalance that produces lift and creates a problem at the fins tips. The higher-pressure below a fin spills up over the fin tip, into the area of lower-pressure above. The fin’s forward motion spins this upward spill of air into a long spiral, like a small tornado, that trails off the wing tip. These wingtip vortices create a form of pressure drag called vortex drag.
Surfboard fins with dimples creates a turbulent flow. Turbulent flow has more adhesion, so when you start to turn the dimpled foil, the surface delays the flow separation, reducing cavitation (separation bubble) allowing the foil to maintain performance. When the surfer turns at high speeds, the turbulent boundary layer helps the flow overcome an adverse pressure gradient and allows the flow to remain attached to the surface longer than it would otherwise. This reduces drag, increases lift and improves overall performance of the fin design.
3DFINS Patented Dimple Surf Fin design utilizes the turbulent flow created by the dimples on the fins, this turbulent flow draws the fluid back over the fin’s surface, reducing cavitation and drag during extreme changes of direction (high angles of attack) and at high speeds. The improved performance of a fin with dimples allows the surfer to increase the lift, which in turn creates more drive, allows the surfer to maintain their speed and drive through turns, overall increasing performance of the surfboard.
Dimples also reduce and almost eliminate the wingtip vortices, by reducing the separation of flow at the fin’s tip, this also helps to increases the lift and overall performance of the fin.
CFD test have shown the dimpled fin designs improve lift and drag by up to 15%, which translates to More Drive, More Speed, More Hold, More Fun.