Effect of Loading Level and Distribution on LPT Losses

Abstract

This paper reports the results of an experimental and analytical study dealing with the effect of loading level and distribution on low-pressure turbine (LPT) blade performance. Only a single blade row is considered here, and the study is conducted in a stationary linear cascade that simulates the aero characteristics of a modern LPT design. The loading level and distribution are systematically varied by changing the number of blades (solidity), the stagger angle, and the unguided turning angle. The exit Mach number for this high-speed test is set at 0.64. The Zweifel number ranges from ∼ 1 (nominal lift) to ∼ 1.27 (high lift). The Reynolds number (based on chord and exit velocity) is varied from ∼70,000 to ∼350,000, a range that is broad enough to cover typical cruise and take-off conditions. While some data is taken near the end-walls, the primary focus of this study is on measurements at the mid-span. In addition to the profile loss, measurements include static pressure distribution on the blade surface (loading) and flow visualization. Data demonstrates increased suction side separation and consequent high losses as the loading level increases, the loading is moved aft, or the Reynolds number decreases. Three-dimensional CFD simulations, in conjunction with a turbulence transition model, corroborate these findings.