Experimental and Numerical Evaluation of a Highly-Loaded Multistage Low-Speed Axial Compressor Featuring Tandem Stator Vanes: Part 2 — Rotor Flow Field and Unsteady Flow Phenomena

Abstract Tandem blade configurations allow to achieve higher aerodynamic loading than conventional compressor configurations and therefore enable further reduction in compressor size. However, their use is associated with a more complex flow field and the unsteady behavior, especially in a multistage environment, is yet unknown. Within this paper series, a bladeing concept using conventional rotors and tandem stator vanes is investigated numerically and experimentally on a 3.5-stage low-speed compressor. The first part of the series examines the operational behavior and the steady-state flow field, whereas part 3 concludes with a robustness analysis in terms of degraded total pressure inlet profile conditions. The present part 2 investigates unsteady phenomena in the flow field. The focus is on the experimental investigation of rotor-stator interactions in a multistage compressor using tandem vanes, as well as the characterization of the rotor and the double leakage associated with its tip vortex. The tandem stator flow field is very robust against unsteady inflow conditions downstream of a rotor. However, the tandem gap region, is periodically disturbed by the rotor wake. The rotor flow field itself shows a thin wake and little variations in circumferential direction. The sensitivity of the rotor exposed to the large secondary flow structures of a tandem stator is very small, proving the robustness of the present highly-loaded compressor design in multistage configurations.