The University of Oxford has been working for a number of years on a conceptually new philosophy for HP vane design .
The desired function of the HP vane is to accept flow from a — generally — annular intake, and turn and accelerate it with minimum loss and heat transfer, and with due consideration to mechanical, manufacturing and integration issues. The conventional design process is well-defined: annulus line definition; through-flow analysis; 2D airfoil section definition; vane stack definition; lean/sweep treatments; secondary flow contouring and fillet design; vane and platform cooling system design; integrated aero/thermal/capacity optimization. The process is based on optimizing 2D airfoil stacks to control secondary flows. More recent research (last 20 years) has led to better understanding of airfoil lean, airfoil sweep, leading edge treatments and end-wall profiling. There may be some iterative optimization in which the airfoil sections themselves are modified, but these treatments (as implied by the terminology) are essentially modifications to a 2D airfoil stack which interrupts the upstream annular (most aero-engines) or can-partitioned (most land-based gas turbines) duct.
It is proposed that a more natural design starting point for admitting and accelerating flow with minimum loss (etc.) is a trumpet-shaped flow-path which gradually turns to the desired angle. This approach rejects many traditional concepts in aerodynamics (the sacrosanct nature of the airfoil, concepts of good and bad lift distributions, concepts of vane and platform, etc.), and focuses our attention on the design of a highly-lofted flow-path.
The purpose of this paper is to show that there may be merit in reappraising the starting point for HP vane design, and in investigating Fully Lofted Oval vane (FLOvane) forms of the type described. The corresponding author has not yet heard a good argument against the proposed design philosophy. Despite significantly diverging from conventional wisdom in terms of both process and final geometric form, the following advantages are claimed: improved aerodynamic loss characteristics, reduced heat load, improved cooling performance, improved thermal-mechanical life, improved stage/engine efficiency.
The claimed advantages are justified with detailed numerical analyses of two current industrial gas turbines, compared back-to-back with modified turbines incorporating unoptimised FLOvane designs. Significant performance improvements were observed when FLOvane designs were used.