Computational Design and Experimental Evaluation of Using a Leading Edge Fillet on a Gas Turbine Vane

Abstract

With the desire for increased power output for a gas turbine engine comes the continual push to achieve higher turbine inlet temperatures. Higher temperatures result in large thermal and mechanical stresses particularly along the nozzle guide vane. One critical region along a vane is the leading edge-endwall juncture. Based on the assumption that the approaching flow to this juncture is similar to a two-dimensional boundary layer, previous studies have shown that a horseshoe vortex forms. This vortex forms because of a radial total pressure gradient from the approaching boundary layer. This paper documents the computational design and experimental validation of a fillet placed at the leading edge-endwall juncture of a guide vane to eliminate the horseshoe vortex. The fillet design effectively accelerated the incoming boundary layer thereby mitigating the effect of the total pressure gradient. To verify the CFD studies used to design the leading edge fillet, flow field measurements were performed in a large-scale, linear, vane cascade. The flow field measurements were performed with a laser Doppler velocimeter in four planes orientated orthogonal to the vane. Good agreement between the CFD predictions and the experimental measurements verified the effectiveness of the leading edge fillet at eliminating the horseshoe vortex. The flowfield results showed that the turbulent kinetic energy levels were significantly reduced in the endwall region because of the absence of the unsteady horseshoe vortex.

Numerical analyses and optimizations on the flow in the nacelle region of a wind turbine

“…The span-wise and chord-wise extent of the corner separation is reduced, but no fundamental change in the topology is visible. As suggested by measurements such as those of Zamir (1981), transition in the corner region is typically earlier than for an equivalent flat plate boundary layer. Hence in reality, where pollution and surface roughness also play a role, the extent of separation might lie between that predicted by the fully turbulent and the transitional simulation.…”

“…Accounting for cross-flow-induced transition shall be referred to the criteriabased model of Arnal and Juillen (1987) or the recent extensions of the γ -Re θ model by Grabe and Krumbein (2014) and Langtry (2015). Measurements such as those of Zamir (1981) further suggest an earlier transition to turbulence within corner boundary layers compared to corresponding flat-plate conditions. Nevertheless, in order to assess the firstorder effects of transition on the results, transitional simulations are conducted for the baseline rotor-nacelle configuration by employing the γ -Re θ model and the envelope method of Drela and Giles (1987).…”

“…It was decided to reduce the fillet nose radius to 0.2 m in order to increase the strength of the HSV again, which is believed to be helpful for the reduction of corner separation (Devenport et al, 1992). This is certainly the conservative approach, since the separation should optimally be suppressed in combination with a reduced or even elimi- nated HSV, as the latter increases the interference drag and is a source of noise (Zess and Thole, 2001;Simpson, 2001;Devenport et al, 1992). Towards the trailing edge, the local radius was increased on the suction side to eliminate the unfavorable pressure rise induced by the shape in the transition to the blade previously seen in CaseT1.0-rounded.…”

Controlling secondary flows in very highly-loaded low-pressure turbine cascades

“…In a similar fashion, Zess and Thole (2002) applied a leading edge fillet to a turbine vane. The authors ran simulations on multiple fillet geometries and found a fillet 1 6 high and 2 J long was effective at eliminating the horseshoe vortex.…”

Optimizing the Vane-Endwall Junction to Reduce Adiabatic Wall Temperatures in a Turbine Vane Passage

“…While these previous studies have made detailed total pressure traverses and the work of Rose, et al [5] included hotwire traverses, Zess and Thole [7] fully-resolved mean and turbulent flow measurements for a juncture fillet they applied to a large-scale model of a nozzle guide vane. They designed their fillet using the same CFD package as that reported in this paper with the goal of mitigating the formation of the horseshoe vortex.…”