Reduction of Secondary Flow Losses in Turbine Cascades by Leading Edge Modifications at the Endwall

Abstract

Experimental results are presented which show the influence on the secondary flow and its losses by a profile modification of the leading edge very close to the endwall. The investigation was carried out with a well-known turbine profile that originally was developed for highly loaded low pressure turbines. The tests were done in a low speed cascade wind tunnel. The geometrical modification was achieved by a local thickness increase; a leading edge endwall bulb. It was expected that this would intensify the suction side branch of the horse-shoe (hs-) vortex with a desirable weakening effect on the passage vortex. The investigated configuration shows a reduction of secondary losses by 2.1 percent points that represents approximately 50 percent of these losses compared to the reference profile. Detailed measurements of the total pressure field behind the cascade are presented for both the reference and the modified profile. The influence of the modified hs-vortex on the overall passage vortex can be clearly seen. The results of a numerical analysis are compared with the experimental findings. A numerical analysis shows that the important details of the experimental findings can be reproduced. Quantitative values are locally different. The theoretical approach taken cannot yet be used for an exact prediction of the loss reduction. However, the analysis of the interaction and the resulting tendencies are considered to be valid. Hence, theoretical investigations as a guideline for the design of a leading edge bulb at the endwall are a valuable tool.

Endwall Flows in Transonic Turbine Cascades

“…SL2F produces larger losses than SL2P from about 12% to 35% span, and the midspan losses increase by about 10% for both cases. The pitch-averaged loss trends in the current data sets are similar to the results of Sauer et al (2001), who investigated the effects of endwall leading edge bulbs on secondary flows; in their study, the secondary loss reduction was mainly attributed to the intensification of the suction-side leg of the horseshoe vortex, resulting in a weaker passage vortex.…”

“…The application of leading edge bulbs to the T106 airfoil ( Figure 2.4) was examined by Sauer et al (2001). The resulting configurations are labelled T106/1 and T106/2 in As mentioned, the modification of the airfoil pressure-surface profile in the present study is mainly aimed at reducing the secondary losses.…”

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

“…Some authors have modified the leading edge region of the endwall to influence the formation of the horseshoe vortex. Sauer et al (2001) tested four leading edge bulb designs applied to the T106 airfoil in a linear cascade. They found that the bulb increased the strength of the suction-side leg of the horseshoe vortex (V s h), which counter-rotates relative to the passage vortex.…”

Improving Purge Air Cooling Effectiveness by Engineered End-Wall Surface Structures—Part II: Turbine Cascade

“…Han and Goldstein [24] used fillet geometry around the blade leading edge, which removes the horseshoe vortex and reduces the heat transfer near the leading edge. Sauer and Wolf [25] employed a bulb geometry onto an inlet guide vane. The bulb design strengthens counter vortex, which counter-acts the passage vortex.…”