Investigation of endwall flow mechanisms and loss sensitivity analysis in high-load variable geometry turbines under different key geometric parameters of local clearance

As a core component of variable cycle engines, the variable geometry turbine (VGT) modulates turbine operation by adjusting guide vane installation angles, ensuring efficiency and fuel economy under off-design conditions. However, unlike fixed-geometry turbines, VGT inevitably introduces clearances and rotation shafts, significantly altering internal flow fields. While existing research predominantly examines the presence/absence of local clearances in conventional-load turbine guide vanes on overall performance, systematic quantification of key geometric parameters (position, length, height) influencing end wall loss characteristics and flow mechanisms in highly loaded VGT blades remains scarce. This study employs numerical methods validated experimentally to investigate end wall flow dynamics and loss mechanisms under varying local clearance parameters. Three loss indicators were used to establish multivariate regression models at different vane installation angles. Sensitivity analysis following model validation quantified geometric parameter weights affecting distinct losses across operating conditions. Results demonstrate that increased clearance streamwise length elevates leakage flow ratio: energy injection from the pressure side weakens passage vortex intensity while strengthening leakage and wall vortex, causing secondary flow losses to initially decrease before rising. Greater clearance height expands leakage flow area, markedly enhancing vortex intensity and circumferential influence (particularly sensitive at negative installation angles), radially lifting the wall vortex with decelerating leakage growth but accelerating secondary losses. Symmetrical clearances about the rotation shaft minimize leakage and secondary losses; longer upstream clearances maximize wall vortex intensity and losses; longer downstream clearances maximize leakage yet suppress suction-side boundary layer separation. This work provides advanced theoretical foundations for VGT loss control and design optimization.