Influence of Scallops on Windage Loss and Flow Characteristics in Disk-Type Gap

Windage loss and flow characteristics in a disk-type gap featuring scalloped structures are investigated in this paper. Special attention is paid to the size of the scallops and the associated loss models. The respective losses and scallop effects in the gap are explored with various combinations of depths, quantities, and rotating speeds. The results indicate that scallop structures positively contribute to increased windage losses, accounting for more than 60% of the overall losses. An internal spiral vortex band is formed along the scallop wall, with the scallop depth ratio exerting influences on loss, reaching a maximum of 8.1%. The current scallop loss model overlooks the consideration of the total arc length ratio of scallops to the circumference, presenting a limitation, and the maximum relative deviation from numerical simulation results is observed to be 111.4%. An increase in arc length ratio results in a higher total loss, although the loss per individual scallop is diminished, manifesting in reduced vortices and pressure differences. Furthermore, a modified model is proposed to increase the precision of the current loss model. The maximal relative deviations of 13.8% confirm that the modified model is accepted to predict the windage loss in disk-type gaps with scallops. The conclusions offer valuable insights into the structural design of impellers and high-speed electrical machines with superior efficiency.