The Effect of Axial Flow Velocity on Annular Gap Windage Power Loss

As surface speeds of electrical machinery increase to meet ever more demanding application requirements, windage power losses due to shearing of air (or other process fluid) between the rotor and stator take on an increasingly significant role. Historically, these losses have not received a huge amount of research attention from the high speed motor community. Common approaches include making the rotor and stator surfaces as smooth as possible, keeping the rotor-stator gap as large as practical without compromising electrical efficiency, and simply accepting whatever losses are present. This paper presents a combined Computational Fluid Dynamics and experimental evaluation of the effect of axial flow on windage power loss in a rotor-stator gap. The results support other results in the literature suggesting that careful tuning of axial flow velocity in the gap can suppress the formation of turbulent Taylor vortices, and thereby reduce windage power loss. In specific cases, reductions in windage power loss of up to 30 percent have been predicted. The presence of an optimal axial flow velocity is confirmed experimentally.