Loss Reduction in an Ultra-High-Loaded Low Pressure Turbine Cascade by a Combined Flow Control Strategy

Modern low pressure turbines (LPT) always suffer from unexpected endwall flow losses due to the enhanced aerodynamic load. Thus, there is a demand for much more efficient methods to improve the endwall performance of modern LPT. In this paper, a novel flow control method (denoted by FILLET&NEC) which combines leading edge fillet configuration (denoted by FILLET) and non-axisymmetric endwall contouring (denoted by NEC) was applied to an ultra-high-loaded LPT cascade (denoted by REF, Zweifel = 1.59) to explore its flow control potential and underlying mechanisms for endwall secondary flow control. Numerical investigation verified by experiments was used to make comparisons of flow control effects in FILLET, NEC, and FILLET&NEC. Based on the coupled design of FILLET&NEC’s 5 design parameters, Latin hypercube sampling was used for parametric research to get the preferred model. The results show that the total pressure loss coefficient and non-dimensional secondary kinetic energy are reduced by 15.07% and 40.09%, respectively, with the application of FILLET&NEC. This coupled design significantly suppresses the development of passage vortex and wall vortex, while the overturning and underturning of outlet flow angle is reduced. The introduction of NEC effectively reduces the cross-passage pressure gradient near endwall, making up for FILLET’s shortcomings. Simultaneously, FILLET helps NEC decrease the size and strength of horseshoe vortex, improving the flow conditions in cascade passage. Coupled design FILLET&NEC fully highlights the advantages of FILLET and NEC, while avoids their own shortcomings when independently applied. This paper confirmed that the combined design of FILLET and NEC is effective in reducing the endwall secondary losses, providing a valuable reference for the coupled design applications and future advanced ultra-high-loaded LPT designs.