Unsteady influences of blade loading distribution on secondary flow of ultra-high-lift LPT

Abstract

Experimental measurements were performed to study the influence of blade loading distribution on the aerodynamic performance of an ultra-high-lift low-pressure turbine cascade (Zw = 1.58) in the presence and absence of incoming wakes. The flow structures in front-loaded and aft-loaded blade passages were comprehensively compared at various Reynolds numbers. Furthermore, the flow mechanisms responsible for the effect of the blade loading distribution on the secondary flow were discussed in detail through numerical calculations. At the low Reynolds number of 25,000, weaker secondary flow was observed for the aft-loaded blade under steady conditions owing to the lower cross-passage pressure gradient compared to the front-loaded blade. Unsteady wakes clearly improved the throughflow characteristics of the cascade passage, increased the blade loading, and strengthened the secondary flow in the aft-loaded blade passage. At the high Reynolds number of 100,000, unsteady wakes delayed generation of the passage vortex in both the front-loaded and aft-loaded blade passages and clearly weakened the secondary flow. The experimental results revealed that the upstream wakes reduced the strength of the passage vortex core in the aft-loaded and front-loaded blade profiles by 21.6% and 17.5%, respectively.