Visualization of flow behavior in rotating coaxial cylinders with axial slits

Abstract

Toward the improvement of performance of an electric vehicle (EV), the design of the motor shape appropriate to heat removal is important. A typical EV motor is composed of a pair of coaxial cylinders with a fixed outer cylinder (stator) and a rotating inner cylinder (rotor). Some EV motors have axial slits on the stator wall. The present study experimentally clarifies the influence of inner shape on flow behavior in the EV motor. We divided the measurement area into three regions: the gap region, the rotor end region, and the gap end region. The flow behavior was recorded by a high-speed video camera and was measured via PIV. The flow behavior in the gap and rotor end regions were observed by Kalliroscope flakes. Taylor-Couette flow was observed in the gap region for the both cases without and with slits. In the rotor end region, the vortex that spirally flows from outer cylinder to the inside cylinder was observed. The white dye, injected in the gap, remained at the injection point for the cases without slits. However, the dye moved from the gap region to the rotor end region for the cases with slits. The vortex structure directed to the rotating axis was observed in the slit on the stator wall; the vortex had the axial velocity from the gap region to the rotor end region.