脉冲来流致径流涡轮非定常流场畸变效应与流动损失机理

Engine downsizing of Internal Combustion Engine makes a turbocharger turbine to be fed by dramatically pulsating flow, which further enhances the unsteadiness as well as the flow interaction in the volute and the rotor. Therefore, the mechanism of the flow loss in the turbine under pulsating conditions are significantly different from the situation of steady conditions. So far there is very limited investigation focusing on the flow interaction and the consequent flow loss in the turbine under pulsating conditions. This project targets at unveiling the mechanism of turbine performance deterioration under pulsation via the investigation of the flow interaction between unsteady flow distortion in the volute and the vortices evolution in the rotor. Firstly, the mechanism of the unsteady flow distortion in circumferential and axial directions caused by the mass accumulation and the unsteady response of passage vortices is discussed, respectively; next the influence of the unsteady flow distortion on the vortices evolution in the rotor is studied, followed by the detailed investigation of correlation of vortices evolution and the flow loss in the rotor. The contribution to the flow loss by the vortices evolution thus the different flow distortions is quantified by the analysis of entropy generation in the rotor. The investigation is to unveil the mechanism of the performance deterioration of turbine under pulsating conditions, via which lights can be shed on the innovations of flow control methods for performance improvement of turbocharger turbine.

内燃机缩小排量技术使增压器涡轮面临强瞬变的排气脉冲来流，蜗壳与叶轮的非定常流动特征及流场耦合效应显著增强，造成涡轮流动损失机理明显异于稳定来流。现有针对脉冲来流的涡轮研究中鲜见考虑涡轮内部非定常耦合流动及其对流动损失影响的报道。本课题旨在通过蜗壳非定常流场畸变与叶轮旋涡演化耦合流动的研究揭示脉冲来流致涡轮性能异化的机理。结合实验与理论分析，探明脉冲来流的总压瞬时变化导致蜗壳气流累积与通道涡非定常响应，进而形成周向和轴向两个空间维度上的非定常流场畸变效应的机制，探讨蜗壳非定常流场畸变对叶轮旋涡流动生成条件和发展环境的影响规律，及其对旋涡演化过程的影响规律和机理，并通过叶轮旋涡演化和流场熵增分布的关联定量分析不同旋涡流动、畸变分布形式造成流动损失的所占比重，揭示脉冲来流导致涡轮性能异化的非定常流动机理，为发展针对脉冲来流的涡轮增效流动控制方法提供理论依据。

内燃机缩小排量技术使增压器涡轮面临强瞬变的排气脉冲来流，蜗壳与叶轮的非定常流动特征及流场耦合效应显著增强，造成涡轮流动损失机理明显异于稳定来流。现有针对脉冲来流的涡轮研究中鲜见考虑涡轮内部非定常耦合流动及其对流动损失影响的报道。本课题结合实验与理论分析，探明了脉冲来流条件下涡轮非定常性能的变化规律以及脉冲压力波在涡轮内的传导规律，发现脉冲频率和幅度与涡轮性能非定常度正相关；构建了可预测脉冲来流条件下的涡轮非定常性能模型以及蜗壳出口流场非定常畸变的理论分析模型；揭示了总压瞬时变化导致蜗壳气流累积与通道涡非定常响应形成周向和轴向两个空间维度上的非定常流场畸变效应的机制，以及该非定常畸变对涡轮性能的影响，提出了通过非线性A/R分布补偿因非定常效应引起流场畸变的蜗壳流动控制新思路。试验结果表明，采用该方法的涡轮在流通能力保持与原型基本一致的前提下在脉冲来流条件时最高可提高7.3%。该研究为发展针对脉冲来流的涡轮流动控制方法提供理论依据和方向。