Unsteady Flow Measurement in a Shrouded Stator Cavity of Multistage Axial Compressor

Abstract

3D unsteady velocity measurement has been conducted inside the shrouded stator cavity of multistage axial compressor to investigate unsteady velocity distribution inside the cavity by experiment data. Measurement has been conducted using 45-degree slanted hot wire to obtain 3D velocity inside the cavity. By studying ingress and egress of the leakage flow from the cavity, losses which occur near the stator hub can be understood more specifically. According to previous researches, radial velocity distributions are dissimilar for different axial position because of the centrifugal force from rotating part. To investigate precise 3D flow structure, therefore, measurements have been conducted on 3 different axial positions for upstream and downstream of stator. It is revealed that flow inside the downstream cavity is distributed non-uniformly in circumferential direction. According to the data at main passage, tangential velocity in stator hub-corner separation region is smaller than that of other region. Thus, centrifugal force to positive radial direction inside the stator separation region is decreased and it induce more ingress to the cavity. This non-uniform flow distribution is captured by radial velocity distribution in meridional view of downstream cavity. Also, rotor blades affect to the flow which result in unsteady flow features. To comprehend this unsteady characteristics, blade passing period is divided by 20 segments and effect of the rotor blades has been studied. Since pressure around rotor leading edge is high, the egress region is shrunk as rotor leading edge approaches. Flow inside the upstream cavity is affected by upper rotor wake, which is moving in rotating direction. Two strong local vortices are made inside the rotor wake region, and local ingress and egress are induced by these local vortices. To figure out the effects of mass flow rate, experiments on 3 different flow coefficients are conducted at mid-section for both cavity. As flow coefficient is changed, the strength of stator separation region varies, and this affect to the position where egress happen inside the downstream cavity.