Effect of axial skewed slot casing treatment in a transonic fan

Abstract

This paper reports on a time-accurate numerical investigation of axial-skewed slot casing treatment in a high-speed axial fan. Twenty-two axial and radial skewed slots are placed over the casing of the rotor and choke to stall unsteady computations are conducted. Results show that endwall fluid is absorbed by the slots from the downstream part of the blade passage and is injected to the upstream part with a swirl contrary to the blade rotation. This gives the injected fluid a great circumferential velocity component in the relative frame of reference. The shock is, hence, pushed toward the trailing-edge plane and the pressure difference between the pressure and suction surfaces is reduced. Consequently, the occurrence of the leading-edge vortex spillage, which is believed to be the key to stall initiation for the current rotor, is postponed to lower mass flow rates.