低雷诺数涡轮气热耦合仿真及被动优化技术研究

Research on low Reynolds number turbine gas-thermal coupling simulation and passive optimization technology

针对低雷诺数下涡轮发动机气动效率低、热负荷高的问题,以带有径向冷却通道的NASA-MarkⅡ型高压涡轮导叶为研究对象,开展基于凹槽和球窝的被动优化技术研究。利用计算流体力学(CFD)数值模拟技术,对NASA-MarkⅡ进行全三维气热耦合仿真计算,结合已有NASA实验数据进行验证。结果表明:在换热特性方面,低雷诺数条件下凹槽叶形可以有效改善叶片叶根附近流体的换热特性,降低叶根处的热负荷,凹槽深度越大,换热特性的优化效果越明显;在气动性能方面,球窝结构的叶形优化效果更好,其中深径比小、深度大的球窝叶形减小总压损失的效果显著。

The rapid development of aviation gas turbine engine technology has been accompanied by a range of associated challenges.Firstly,as the thrust-to-weight ratio and thermal efficiency of gas turbines increase,the inlet temperature of the turbines also continues to rise.This results in turbine blades being subjected to prolonged exposure to high temperatures and significant thermal loads,making them prone to deformation and ablation.Secondly,when an aircraft is in high-altitude cruise mode,the gas turbines operate at low Reynolds number levels for extended periods.Under these conditions,the laminar boundary layer on the suction side of the turbine guide vanes has weak separation resistance,leading to flow separation under adverse pressure gradients.This can result in the formation of separation bubbles or even open separation,reducing the aerodynamic performance of the blades and subsequently impacting the efficiency of the engine.Therefore,it is essential to improve the efficiency of gas turbines under low Reynolds number conditions and to mitigate the thermal loads experienced by the blades during operation.Research into the aerodynamic performance and heat transfer characteristics of gas turbine guide vanes under low Reynolds number conditions is of great importance.Current mainstream research focuses on enhancing the aerodynamic efficiency of aircraft engine turbines under normal Reynolds number conditions.However,domestic research on the aerodynamic efficiency of gas turbines under extremely low Reynolds number conditions is limited.This is a scenario that cannot be overlooked,especially for engines that frequently operate in high-altitude cruise states.Most existing research has optimized the aerodynamic performance or heat transfer characteristics under low Reynolds number conditions through single-direction design analysis.However,the study of turbine guide vanes cannot solely focus on improving the aerodynamic performance of the blades without considering the impact on blade temperature.Therefore,it is crucial to analyze and optimize the aerodynamic performance and heat transfer characteristics of the blades through a thermo-fluid coupling approach.To achieve this goal,we have chosen the NASA-MarkⅡhigh-pressure turbine guide vanes with radial cooling channels as the research subject.We have conducted passive optimization technology research based on dimples and spherical cavities.Utilizing computational fluid dynamics(CFD)numerical simulation technology,we performed full three-dimensional thermo-fluid coupling simulations for the NASA-MarkⅡunder various Reynolds number conditions(Re=1.2×10^(4),1.9×10^(4),5.6×10^(4),1.9×10^(5),1.9×10^(6))and validated the results with existing NASA experimental data.The results indicate that,in terms of heat transfer characteristics,dimpled blade shapes can effectively improve the heat transfer characteristics of the fluid near the blade root at low Reynolds numbers.This reduces the thermal load at the root,with the optimization effect becoming more pronounced as the dimple depth increases.In terms of aerodynamic performance,the blade shape optimized with spherical cavities shows better results.Specifically,a smaller depth-to-diameter ratio and larger depth cavities exhibit a significant reduction in total pressure loss.In conclusion,the research conducted on the NASA-MarkⅡhigh-pressure turbine guide vanes demonstrates the critical importance of considering both aerodynamic performance and heat transfer characteristics in the design of turbine blades for aviation gas turbine engines.The findings contribute to the body of knowledge in the field and provide practical insights for engineers and designers seeking to optimize engine performance under a wide range of operating conditions.As the aviation industry continues to advance engine technology,our research plays an increasingly vital role in ensuring the efficiency,reliability,and safety of future generations of aircraft.