Experemental And Numerical Study Of The Transonic Cooled Turbine Blades

Abstract

Modern gas turbines operate at high temperatures, which exceed the endurance limit of material, and therefore the turbines components are cooled by the air taken from the compressor. The cooling provides positive impact on lifetime of GT has negative impact on its performance. In convection-cooled turbine blade the coolant is usually discharged through the trailing edge and it leads to limitation on the minimal size of trailing edge and thereby negatively affects the losses. Moreover, the injection of cooling air in the turbine disturbs the main flow, and may lead to additional increase of losses, and the trailing edge loss is a significant part of the overall loss in modern gas turbines. This study comprises investigations of losses in cooled blades. Four cascades with different unguided part of aerofoil with and without coolant injection were studied both experimentally and numerically. This analysis provides split of losses caused by different factors, and offers the opportunities for efficiency and lifetime improvements of real engine designs/upgrades. In particular it is shown that an increase in the unguided turning angle results in a reduction of loss in case of relatively thick trailing edge. It is also shown that injection through the trailing edge slot parallel to the main flow leads to neutral loss impact and even loss reduction in subsonic range and loss increase in the supersonic range of exit Mach numbers. KEAWORDS: cooled transonic blade, profile losses, unguided flow angle impact, cooling air injection NOMENCLATURE a2-throat width Cx-axial chord length Cpb-base pressure coefficient c-velocity d2-trailing edge thickness d2/a2-ratio of trailing edge diameter to throat width L-true chord length Loss-profile energy loss M-Mach number P0-total pressure P-static pressure Pb-base pressure P2av-averaged exit static pressure R-gas constant Re-Reynolds number s-coordinate along wetted surface of profile T0-total temperature t-pitch Tu-turbulence intensity w2-trailing edge wedge angle z-distance between planes Subscripts 1-row inlet 2-row exit Abbreviations LE-leading edge PS-pressure surface SS-suction surface TE-trailing edge is-isentropic Greeks 1m-inlet metal angle 2e-outlet effective angle; 2e = arcsin(a2/t) γ-stagger angle δ-unguided turning angle or uncovered turning θ-perimeter of aerofoil k-specific heat ratio ν-kinematic viscosity