Time-resolved vane-rotor-vane interaction in a transonic one-and-a-half stage turbine

Abstract

This paper describes the effect of both an upstream and a downstream vane on the time-resolved surface pressure field around a high-pressure rotor blade. The geometry of the downstream vane considered is a large low aspect ratio vane located in a swan-necked diffuser duct, similar to those likely to be used in future engine designs. Two test geometries are considered: firstly, a high-pressure turbine stage coupled with a swan-necked diffuser exit duct; secondly, the same high-pressure stage but with a vane located in the downstream duct. Both tests were conducted at engine-representative Mach and Reynolds numbers, and experimental data were acquired using fast response pressure transducers mounted on the mid-height streamline of the high-pressure rotor blades. It is shown that the potential field of the downstream vane causes a relatively large static pressure fluctuation on the late rotor suction surface but that the early suction surface and pressure surface are unaffected by the presence of the vane. In addition to the two main interaction mechanisms (upstream vane-rotor and downstream vane-rotor interactions) a third interaction is identified. This is shown to be caused by the interaction, within the rotor passage, between the flowfield associated with the upstream vane and the potential field associated with the downstream vane. This new interaction mechanism is shown to cause static pressure fluctuations on the late rotor suction surface at a frequency corresponding to the difference in the numbers of upstream and downstream vanes.