Stall analysis in a transonic compressor stage and rotor

Abstract

Gas turbine engine design is based on simplifying assumptions, including axi-symmetric flow. These assumptions break down in the real machines especially when operating near to stall. The reduction in operating surge margin associated with current trends to develop high performance military fighter aircraft further highlights the need to develop a thorough understanding of the flow in rotor blade passages and especially when operating close to stall. This research investigates the behavior of a Transonic Compressor Rig (TCR) as it approaches stall in the rotor-only and full-stage configuration using combinations of frequency and time domain analysis in the subsonic (70% rated speed), sonic (80% rated speed) and transonic operating ranges (90%, 95%, and 100% rated speed). A steady-state analysis of the pressure measurements across a rotor passage of the TCR was conducted to identify potential pre-stall indicators, the structure of the flow field within the blade passages, and to correlate changes in flow structure with changes in pressure measurements. Further investigation using flow visualization techniques within the blade passages demonstrated how the TCR rotor departed from an idealized rotor when the axi-symmetric assumption holds when operating at steady-state and near stall conditions. This identification of potential stall indicators and characterization of the time variant flow field within the passages will impact future compressor design to enable operation closer to stall and increased performance across an operating spectrum.