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This paper describes an experimental investigation on a state-ofthe-art compressor airfoil with three different leading edges at high subsonic flow conditions. In addition to a conventional circular and elliptical geometry which possess curvature discontinuities at the blend points, a continuous curvature leading edge is studied. The investigation considers the performance at design incidence, as well as the impact of off-design incidences. Pressure spikes near the leading edge can lead to early transition associated with higher profile losses. Goodhand and Miller [1] showed that in low subsonic conditions the avoidance of curvature discontinuities can diminish pressure spikes and therefore reduce the profile losses and enlarge the working range. In this paper, measurements are conducted to assess the potential of this concept for a high-pressure jet engine compressor airfoil operated at high subsonic conditions (M1 = 0.7, Red/2 = 20,000). The results show that, at design incidence, the total pressure loss coefficient of the continuous curvature leading edge reduces by up to 15.4 % compared to the circular leading edge and by up to 3.1 % for the elliptical geometry. At off-design incidence, the reduction can be up to 40.2 % at maximum positive incidence under consideration. NOMENCLATURE AV DR Axial velocity density ratio [-] b Chord length [m] c Absolute velocity [m/s] d Leading edge thickness [m] Dspike Spike diffusion factor [-] i Incidence angle [deg] h Blade height [m] H12 Shape factor [-] l Leading edge length [m] ṁ Mass flow rate [kg/s] M Mach number [-] MP Measuring plane n Direction normal to surface [m] t Pitch [m] p Pressure [Pa] Re Reynolds number [-] s Profile contour coordinate [-] T Temperature [◦C] t Pitch [m] Tu Turbulence intensity [%] u Velocity in flow direction [m/s] v Velocity perpendicular to flow direction [m/s] w Velocity in spanwise direction [m/s] x Axial direction [m] x′ Coordinate in chord direction [m] y Pitchwise direction [m] z Spanwise direction [m] α Flow angle (pitchwise) [deg] γ Heat capacity ratio [-] γ Flow angle (spanwise) [deg] ∆ Difference δ1 Displacement thickness [m] δ2 Momentum thickness [m] δ3 Energy thickness [m] κ Curvature [1/m] ν Kinematic viscosity [m2/s] ω Total pressure loss coefficient [-] ρ Density [kg/m3] Subscripts 1 Inlet 2 Outlet cont.curv. Continuous curvature leading edge ax Axial circular Circular leading edge corr Corrected elliptical Elliptical leading edge is Isentropic max Maximum min Minimum norm Normalized PS Pressure side s Static SS Suction side t Total INTRODUCTION Efficiency improvement has been the main driver in compressor development for decades. Even though the further potential for improvement has decreased over the years due to a better understanding of the compressor flow, increasing fuel costs justify further research on advancements. Nowadays, multiple disciplines and aspects are considered, especially the product life cycle, and maintenance, repair and operations (MRO) aspects are assessed. For years, the development of new airfoils neglected the potential of optimized leading edges. Instead, circular leading edges were used since they are easy to manufacture and resistant to erosion or other damages. It was International Journal of Gas Turbine, Propulsion and Power Systems October 2020, Volume 11, Number 4 Presented at International Gas Turbine Congress 2019 Tokyo, November 17-22, Tokyo, Japan Review Completed on , September 17, 2020 Copyright © 2020 Gas Turbine Society of Japan

Performance Analysis of a Compressor Leading Edge without Pressure Spike at High Subsonic Speed