Unsteady Investigation of the Effect of Purge Air on the Flow Field Inside a Turbine Vane Frame Using Particle Image Velocimetry

Abstract

Reducing greenhouse gas emissions and high fuel expenses motivates manufacturers to design more efficient aircraft engines. For directly driven jet engines, this is possible through increased bypass ratios for high propulsive efficiencies. This implies a change in the operating condition of the lowpressure turbine (LPT) toward lower rotational speeds at larger diameters. Turbine vane frames (TVFs) guide the airflow from the highpressure turbine (HPT) to the LPT in radial and circumferential direction. The TVF setup integrates turning vanes and thus removes the need for a vane blade row in the first LPT stage. Consequently, the TVF yields a benefit for overall engine weight and length, resulting in overall efficiency gains. Experimental measurements have been conducted at the twospool test rig at the Graz University of Technology, consisting of a singlestage HPT, the TVF, and the first LPT rotor. Enginerelevant flow conditions are achieved at the TVF inlet, including HPT tip clearance and purge air effects. Particle image velocimetry (PIV) was used to capture the flow field in between two struts of the TVF upstream of the splitter vanes. Flow data in the area of strong transient interactions between the HPT and the TVF are recorded and discussed in terms of aerodynamic performance. To reveal the unsteady behavior of the fluid, the flow field has been recorded at six serial stator–rotor positions. Two data sets of varying HPT purge flows were obtained to characterize the effect of purge air inside the measurement domain.