Interaction Between the TVF-LPT Hub Cavity With the Mainflow

Abstract This paper aims to provide insight into the complex interaction between a low-pressure turbine (LPT) hub forward cavity and the mainflow downstream of an intermediate turbine duct with turning struts, also known as a turbine vane frame (TVF). This serves as a structural link connecting the last high-pressure turbine stage to the first low-pressure turbine stage, functioning as a vane row for the latter. In addition to the struts, the examined TVF geometry features one splitter per strut passage. The investigations were carried out experimentally and numerically. The experiments took place at the transonic turbine test facility (TTTF) of the Institute of Turbomachinery and Machine Dynamics at Graz University of Technology. The two-spool test rig consists of a fully purged, unshrouded high-pressure turbine followed by the TVF and the hub forward purged LPT. Further, the TTTF secondary air system (SAS) can inject tracer gas (CO2 or N2O), which enables the seed-gas measurement technique. These well-established measurements are presented for two different rim seal configurations downstream of the LPT. Additional insights were drawn from the URANS simulation of the TVF-LPT component. This simulation was modified in order to perform a numerical tracer gas study, which was validated with the measurements. The experimental results show a good agreement with the numerical investigations, therefore the CFD enables further insight into the flow cavity – mainflow interactions. It was found that both rim seal designs lead to a distinct purge streak at the LPT outlet at the same circumferential position. Furthermore, the rim seal with the larger axial clearance showed a pronounced mainflow ingress, leading to condition without sealing.