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. Efficiency can be improved for directly driven jet engines through increased by-pass ratios for high propulsive efficiencies. This measure implies a change in the operating condition of the low-pressure turbine (LPT) towards lower rotational speeds at larger diameters. Turbine vane frames (TVFs) guide the airflow from the high-pressure turbine (HPT) to the LPT in the 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 benefits the engine weight and length, resulting in efficiency gains. Experimental measurements have been conducted at the two-spool test rig at the Graz University of Technology, consisting of a single-stage HPT, the TVF, and the first LPT rotor. Engine-relevant 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 interactions between the HPT and the TVF was recorded and discussed in terms of aerodynamic performance. To reveal the unsteady behavior of the fluid, the flow field has been recorded for 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.