Design optimization method for variable geometry turbines considering multi-operating conditions

• Design optimization method for variable geometry turbines is proposed. • Method for precise estimation of stator throat and outflow angle is presented. • Kriging-based multi-objective aerodynamic optimization of rotor is conducted. • Efficiencies of a prototype turbine are notably improved under high- and low- mass conditions. The variable geometry turbine (VGT) is a key promising technology for variable cycle engines to flexibly switch operating modes to achieve high specific thrust and low fuel consumption. Despite being critical, preliminary design and blade optimization remain underexplored for the VGT. In this work, an aerodynamic design, analysis and optimization method for VGTs that effectively accounts for multi-operating conditions was proposed, which integrates inverse design at ‘Open’ condition and performance estimation at ‘Closed’ condition. Additionally, a systematic approach for choke determination and throat calculation was developed, ensuring precise flow regulation across a broad range of stator rotation angles. Based on this framework, a parametric analysis of several key decision variables was conducted and Pareto fronts describing the trade-off between overall efficiency and regulation capability were derived. Results indicate that low reaction degrees improve regulation capability, while moderately high reaction degrees improve efficiency. Furthermore, a Kriging-based multi-objective genetic optimization algorithm was employed to optimize the rotor blade, showing that the stagger angle plays a crucial role in rotor performance, with higher values favoring positive incidence angles. The proposed method was applied to a prototype turbine, improving the efficiency by 0.75% at 100% flow condition and by 2.49% at 66.6% flow condition.