Reduction of secondary flow losses in turbine cascades by leading edge modifications at the endwall

Experimental results are presented which show the influence on the secondar y flow and its losses by a profile modification of the lending edge very cl ose to the endwall. The investigation was carried out with a well-known tur bine profile that originally was developed for highly loaded low pressure t urbines. The tests were done in a low speed cascade wind tunnel. The geomet rical modification was achieved by a local thickness increase; a leading ed ge endwall bulb. It was expected that this would intensify the suction side branch of the horse-shoe (hs-l vortex with a desirable weakening effect on the passage vortex. The investigated configuration shows a reduction of se condary losses by 2.1 percent points that represents approximately 50 perce nt 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 modi fled hs-vorte x on the overall passage vortex can be clearly seen. The results of a numer ical analysis are compared with the experimental findings. A numerical anal ysis shows that the important details of the experimental findings can be r eproduced. Quantitive values are locally different. The theoretical approac h taken cannot yet be used for an exact prediction of the loss reduction. H owever, the analysis of the interaction and the resulting tendencies are co nsidered to be valid. Hence, theoretical investigations as a guideline for the design of a lending edge bulb at the endwall are a valuable tool.