Numerical study on the internal flow mechanisms of variable geometry high-load low-pressure turbine cascade under wide operating conditions

Variable geometry turbines (VGTs) serve as critical components in adjustable aeroengines. In this work, validated numerical simulations are employed to systematically study the internal flow mechanisms of an adjustable high-load low-pressure turbine vane across varying installation angles, and the local clearance effects are analysed under practical operating conditions. The results reveal that high-load blades demonstrate enhanced flow adaptability compared with conventional designs, achieving a flow modulation range of 55.5 %-135.5 %. This improved adjustability stems from the amplified transverse pressure gradients within the blade passages, and these gradients intensify the endwall secondary flow losses (proportionally higher in total losses) and generate complex vortical structures, including passage vortices (PVs), trailing-edge vortices (TVs), and corner vortices (CVs). Extreme positive angles induce pressure‒surface separation vortices (SVs) with spanwise propagation; this increases the aerodynamic losses through channel blockage. Conversely, reduced angles primarily cause suction–surface separation near the leading edges, where the separation losses surpass the mid-chord flow detachment effects. Local clearance exhibits dual functionality: moderately expanding the inter-blade passage area to enhance the flow capacity while generating leakage vortices (LV) that interact with the endwall vortices. At reduced angles, the LV intensity inversely correlates with the flow rate, and the loss mechanisms are dominant in the low-flow regimes. The clearance-induced loss regions exhibit radial downwards migration across all angles, and the LV‒PV interactions intensify the secondary losses between 0.02<z/h < 0.04. These findings highlight the inherent compromise between the flow adaptability and loss accumulation in VGTs, particularly under off-design operating conditions.