A Novel Design towards Reducing Leakage Loss for Variable Geometry Turbines

Abstract

To accommodate the next generation of adaptive/variable cycle engines and gas turbine power, the variable geometry turbine (VTG) is widely acknowledged as a most essential component. VGT consists of an adjustable vane to address the combined goals of high dry thrust and low specific fuel consumption (SFC) at subsonic cruises for aero-engines. This concept allows an engine to operate at a constant bypass ratio over a wide range of pressure ratios. To avoid scraping during rotation for guide vanes, a typical gap is deliberately left, which leads to significant leakage loss. In this research work, a novel spherical convex plat with a pivot shaft is proposed, which can be obtained by additive manufacturing. The plat is sophisticatedly designed according to the aggressive tip/hub pressure gradient. This design naturally generates a blockage for the gas from the pressure side towards the suction side. As a result, the most aggressive pressure gradient is removed, and maximum leakage flow is eliminated. The overall leakage loss is reduced. This simple rotating structure design can improve the efficiency by 0.4–3.0% within the wide range considered. Based on the understanding of the loss mechanism, a radially restacked vane is designed and another extra 0.2% improvement is achieved. This universal design philosophy is also verified on different loading blade profiles, i.e., front-, middle- and aft-loaded turbine vane. The improved aerodynamic performance is achieved with this novel idea.