Experiments on Aft-Disk Cavity Ingestion in a Model 1.5-Stage Axial-Flow Turbine

Abstract

Experiments were carried out in a model 1.5-stage (vane-blade-vane) axial-flow air turbine to investigate the ingestion of main-stream air into the aft disk cavity. This cavity features rotor and stator rim seals with radial clearance and axial overlap, and an inner labyrinth seal. Results are reported for two main air flow rates, two rotor speeds, and three purge (secondary) air flow rates. The initial step at each experimental condition was the measurement of time-average static pressure distribution in the turbine stage to ensure that a nominally steady run condition had been achieved. Subsequently, tracer gas concentration and particle image velocimetry (PIV) techniques were employed to measure, respectively, the main gas ingestion into the disk cavity (rim and inner parts) and the fluid velocity field in the rim cavity. Finally, the egress trajectory of the purge air into the main-stream air was mapped in the axial-radial plane by PIV at multiple circumferential positions within one aft vane pitch. The purge air egress trajectory and velocity field are important because the interaction of this air with the main gas stream has aerodynamic, stage performance, and downstream vane/endwall heat transfer implications.