• Bodo Ungerechts
  • Ulrik Persyn
  • Veronique Colman
Keywords: self propulsion, flow visualisation, hydrodynamics, vortex, front/rear driven propulsion, ecconomy


Propulsion in water is based on the interaction of motion body and water, respectively (under the condition of limited energy reservoir). The swimming movements are transmitting momentum creating a flow in the aquatic surrounding. Self-propulsion is a mutual result of a transfer of momentum from the propelling parts of the body on the water as well as a transfer of impulse from the water on the body, producing a counter bearing (a term indicating the application of Newton’s 3rd Law) and leaving thereby some traces. In water the traces are useful for discussions about the efficiency of swimming techniques. Here the traces of vortex (a common term for mass of whirling fluid) are emphasised. Vortices occur in different organized patterns, as trailing vortex next to the hands (front driven body) or rolling vortex in the wake of the feet (rear driven body). Trailing vortex create a zone of underpressure: it is hypothised that the hand is resited by this suction from the intended pull through the water and thus the action of the trunk-arm muscles propels the body past the hand. Rolling vortex may transfer a power stroke to the body in case the sense of its rotation is altered.