Aerodynamic Performance of Turbine Center Frames With Purge Flows—Part I: The Influence of Turbine Purge Flow Rates

Abstract

This two-part paper deals with the influence of high-pressure turbine (HPT) purge flows on the aerodynamic performance of turbine center frames (TCF). Measurements were carried out in a product-representative one and a half-stage turbine test setup. Four individual purge mass flows differing in flow rate, pressure, and temperature were injected through the hub and tip, forward and aft cavities of the unshrouded HPT rotor. Two TCF designs, equipped with nonturning struts, were tested and compared. In this first part of the paper, the influence of different purge flow rates (PFR) is discussed, while in the second part of the paper, the impact of the individual hub and tip purge flows on the TCF aerodynamics is investigated. The acquired measurement data illustrate that the interaction of the ejected purge flow with the main flow enhances the secondary flow structures through the TCF duct. Depending on the PFR, the radial migration of purge air onto the strut surfaces directly impacts the loss behavior of the duct. The losses associated with the flow close to the struts and in the strut wakes are highly dependent on the relative position between the HPT vane and the strut leading edge (LE), as well as the interaction between vane wake and ejected purge flow. This first-time experimental assessment demonstrates that a reduction in the purge air requirement benefits the engine system performance by lowering the TCF total pressure loss.

Impact of Turbine-Strut Clocking on the Performance of a Turbine Center Frame

“…The LPV N and the counter-rotating peak value of LPV R are forming a vortex pair convected through the duct as a characteristic streak. The previous studies (Zerobin et al [2] or Sterzinger et al [28]) mentioned these streaks as purge flow streaks because they are the relevant structures entraining the HPT purge air and transporting it downstream.…”

“…The circumferentially mass-averaged radial profiles of the presented flow quantities are calculated using Eqs. (1) and (2). The mass flowrate is obtained using the static values received from the 5HP polynomial calibration.…”

“…More recently, Zerobin et al [2] published a study investigating an engine-relevant combined HPT-TCF-LPT vane test configuration, including HPT purge flows. Besides revealing the contributions of the HPT purge interaction mechanisms with the main air to the TCF pressure loss and confirming the findings from Jenny et al [3] and Regina et al [4], Zerobin et al postulated a dependence of the TCF pressure loss on the HPT vane to TCF strut clocking position.…”

“…The flow field downstream of the TCF was acquired over more than one TCF pitch, including two TCF strut wake regions. Figure 1 published in the study by Zerobin et al [2] presents the acquired flow field downstream of the TCF. A comparison of the total pressure loss obtained by evaluating the different flow regions (strut I, core flow, strut II in Fig.…”

“…As the number of HPT vanes was not a multiple of Fig. 1 Relative total pressure loss downstream of a TCF (Zerobin et al [2])…”