Investigating endwall flow mechanisms and improving the loss model under diverse operating conditions

Abstract

Accurate prediction and comprehension of off-design turbine performance hold paramount importance in the development of highly efficient turbines capable of operating across a diverse range of conditions. This research concentrates on a highly loaded turbine cascade endwall flow and endeavors to scrutinize the impact of both incidence angle and inlet free stream turbulence intensity (FSTI). The investigation involves a meticulous analysis leading to substantial improvements in the existing endwall loss model (the Benner model correlated with the Moustapha incidence loss correction model), tailored for off-design scenarios. The findings underscore the pronounced influence of both incidence angle and FSTI on the dynamics of the endwall flow. Notably, alterations in the incidence angle have been identified as exerting a discernible impact on the flow structure, particularly when encountering large positive incidence angles. At an incidence angle of +20°, a distinctive vortex known as the Concentrated Shedding Vortex emerges as a pivotal factor in shaping the endwall flow structure, resulting in a substantial escalation in endwall losses. Furthermore, variations in FSTI predominantly affect the intensity of secondary vortices, thereby influencing endwall loss. Leveraging these discernments, an expressive formulation for endwall loss is derived by refining the higher-order terms of the incidence loss correction model and introducing a corrective term associated with FSTI. It has been validated that the proposed model controls the prediction error of endwall loss within a margin of ±0.02.