Speed suits and surface drag
Fluid dynamics incorporates the study of various sub-disciplines including aerodynamics and hydrodynamics. Though it is one of the less significant factors effecting swimmers’ velocity, surface drag still plays a role in competitive swimming and can be reduced using a few simple methods.
Surface drag (also sometimes referred to as ‘skin friction’) is the result of water flowing backwards along the surface of the body. Surface drag increases linearly with velocity and is influenced by several factors including:
- Relative velocity (speed of the swimmer through the water)
- Surface area parallel to flow (size of the swimmer)
- Surface roughness (hairs)
- Fluid viscosity
Though not nearly as influential as both profile and wave drag (topics for another day), the effects of surface drag in the sport of swimming were well demonstrated in the 2008 Olympics (Speedo’s LZR range).
Though the suits in question are now banned, they worked by reducing turbulent flow around a swimmer through the development of a boundary layer. A boundary layer (the layer of fluid that becomes stuck to the surface of an object) works by reducing the friction experienced by objects moving through a fluid. This occurs as a result of the fluid running against itself, rather than against the material or swimmer.
Though seemingly abstract, boundary layers are also used regularly in golf, with the ball’s dimples assisting in the creation of a boundary layer at higher velocities. This allows the ball to travel further. Speed suits work in a similar fashion.
There have been multiple attempts to increase speed through the reduction of surface drag, from the application of oil, to the shaving of skin. Though the latter can be done easily and has great effect, the best way to reduce surface drag is through the use of a speed suit which will also assist with the development of a boundary layer.