Effect of Non-Uniform Nozzle Vane Tip Clearance on the Aerodynamic Performance of a Supersonic Variable Nozzle Turbine

The clearance of the nozzle vane significantly influences the aerodynamic performance of variable nozzle turbines (VNTs), often leading to increased flow losses and performance degradation. Although nozzle vane clearance often exhibits a non-uniform distribution due to corrosion, wear, machining tolerances, or assembly errors, the aerodynamic effects of such non-uniform clearance have rarely been investigated. This study aims to fill the research gap regarding the influence of non-uniform nozzle guide vane clearance on tip leakage flow and aerodynamic performance in a supersonic VNT. By systematically examining the flow field features under different clearance profiles via three-dimensional numerical simulations, this work seeks to identify a potential clearance configuration that can reduce flow loss and improve turbine efficiency. The flow losses, tip leakage vortex patterns, and the interaction between the leakage vortex and shock waves are analyzed in detail for different clearance profiles. The results indicate that for a rear-loaded vane profile, the shrinking clearance (SC) configuration yields a lower mass flow rate and higher aerodynamic efficiency compared to the expanding clearance (EC) and uniform clearance (UC) configurations. Specifically, the SC configuration effectively reduces leakage mass flow and vortex intensity. Consequently, the interaction between the leakage vortex and the shock wave is suppressed. This suppression significantly mitigates flow losses, which are primarily driven by the shock–vortex interaction rather than the interaction between the leakage flow and the main flow, thereby enhancing aerodynamic performance. These findings suggest that a rational design of non-uniform clearance profiles can substantially improve the aerodynamic performance of supersonic turbines.