Effect of Free-Stream Turbulence on Endwall Flow of Highly Loaded Turbine Cascades in a Wide Range of Incidence

Abstract

Comprehensive understanding of the loss mechanism is crucial for maintaining high turbine efficiency over a wide operation range. This paper explores the coupling effect of the inlet free-stream turbulence intensity (FSTI) and incidence on endwall flow of highly loaded turbine cascades. Numerical study is conducted on PackB cascade with different FSTI (0.4% to 10%) over a wide range of incidence (-40° to +20°). Design condition (i = 0°, FSTI = 2.2%) is chosen as the reference for thorough comprehension. The transformation of secondary vortex structure is analyzed in detail. FSTI and incidence have a more significant impact on endwall flow than on midspan flow; these results have not been previously reported. An interesting phenomenon is observed and analyzed that the number of horseshoe vortexes (HV) increases with a decrease in FSTI. Then endwall loss generation in turbine passage is extracted considering the location of secondary flow separation lines. This research provides a theoretical basis for the design of high-efficiency turbines in a wide operating conditions.