Effect of Upstream Purge Slot on a Transonic Turbine Blade Passage: Part 1 — Aerodynamic Performance

Abstract

In this paper, detailed experimental results of total pressure loss and secondary flow field are presented for a high turning (127°) airfoil passage in presence of an upstream purge slot (with and without coolant injection). The experiments were performed at Virginia Tech’s quasi 2D linear turbine cascade operating at transonic conditions. Measurements were made at design exit Mach number 0.88 and design incidence angle. The selected coolant to mainstream mass flow ratio (MFR) was set at 1.0%. In order to match engine representative inlet/exit blade loading, a diverging endwall was utilized where the span increased from the inlet to the exit at a 13 degree angle. A 5-hole probe traverse was used to measure exit total pressure. Pressure loss coefficients were calculated both along pitchwise and spanwise directions at 0.1 axial chord downstream of the blade trailing edge. CFD studies were conducted to compliment the experimental results. The backward facing step present with the upstream slot affects the approaching boundary layer and influences the passage horse-shoe vortex strength. The addition of coolant from the purge slot further increased the aerodynamic losses. However, the backward facing step of the upstream slot seems to be the predominant factor in affecting pressure losses when compared to with or without blowing cases. These results provide further understanding of the passage secondary flow characteristics and aid towards improved design of endwall passages. The heat transfer experiments, designed to find the heat transfer coefficient and the film cooling effectiveness are described in detail in part II of this paper [1].

Aerodynamic Performance of a Transonic Turbine Blade Passage in Presence of Upstream Slot and Mateface Gap With Endwall Contouring

“…The present study is an extension of the work presented by Abraham et al [21] and Blot et al [22] to incorporate effects of an upstream purge slot and mateface gap on the same linear cascade set-up. The measurements were carried out for a diverging planar endwall (P) as well as two contoured endwalls which shall be henceforth referred to as Aero…”

“…Aero Contour has been tested previously by Abraham et al [21] and Blot et al [22]. A new contour design geometry was also tested this year, which is being referred to here as the OPT1 endwall.…”

“…They concluded that the secondary loses would increase as a result of increasing the pitch by 25% using the same blade profile. Blot et al [22] utilized a similar setup to investigate aerodynamic losses for the cascade in presence of an upstream purge slot. They found that the upstream slot significantly affects the secondary flow.…”

“…Since the study is a continuation from the works of Abraham et al [21]. and Blot et al [22], an identical test section cascade geometry is used. It is a linear cascade consisting of 5 airfoils (total 4 passages), where the passage of interest is between the 3rd and 4th airfoil from the top.…”

“…The upstream purge slot was first tested by Blot et al [22] and as reported, it is located 0.3-Cax upstream of the leading edge of airfoil. Straight parallel vanes were used in order to obtain uniform exit flow as the coolant exits the slot and interacts with the mainstream flow.…”