Design Solutions for Decreasing Blade Tip Clearance Leakage Flow Using Thermomechanical Approach

Abstract Reduction of labyrinth seal clearances over shrouded low pressure turbine blades is essential to achieve high module efficiencies, thereby lowering specific fuel consumption of aero gas turbine engines. Optimization of tip seal clearance must be conducted over a flight mission so that maximum efficiency benefit is attained at critical design points. In the current study, the change in rotor tip seal leakage in different designs was examined with thermomechanical analysis transiently. Various design solutions were tried based on changing part joint type, stator part geometry, rotating part geometry and Secondary Air System (SAS) purge flow. These design solutions were summarized as SAS purge flow from different locations to gain blockage effect, discourager from rotor and stator surfaces, shrouded NGV design and shroud assembly on casing and the effect of part mass change of both stator and rotor. The effect of various designs on rotor tip seal clearance was evaluated. The results, in terms of metal temperatures, SAS air use, clearance levels, module performance, manufacturing and assembly considerations were examined to reach the optimum design from a system level. Finite Element Analysis (FEA), Computational Fluid Dynamics (CFD) and 1D flow network analyses were used to obtain metal temperatures, understand pertinent flow physics and assess clearance levels. A brief summary was presented tabulating the findings. Promising design solutions have shown that, it is possible to reduce rotor tip clearance up to 0.56% of blade height compared to reference geometry. It was observed that design options can improve turbine efficiency up to 0.76% points.