Spin doctors introduce vortex control

摘要

Traditionally, designers have looked at propeller loading levels, frictional resistance on blade surfaces, and the rotating flow of propeller races and by reducing the effects of one or all of these elements the propeller would become more efficient. In contra-rotating, propellers, the rotating flows of the propeller races of the two propellers, arranged one behind the other, cancel each other out by reversing the direction of rotation of the propellers with respect to each other. That is, the efficiency is increased by eliminating the energy loss from the rotational flow. Photo 1 shows the contra-rotating podded propeller propulsion system installed on an NK-classed ship in 2007, according to Class NK.