超声速离心叶轮全流场涡动力模态分解研究

The temporal and spatial evolution of the multi-scale eddy structures in the supersonic impellers of such compressors and its link to the aerodynamic energy loss of the compressors is one theoretical bottleneck that needs to be solved for high performance compressor design and engineering application. This project intends to develop a multivariable Dynamical Mode Decomposition (DMD) method and apply it to the flow information analysis of supersonic centrifugal impellers. The temporal and spatial evolution of the frequency spectra of the eddy structures will be studied and interpolated in flow physics so that a clear relationship between the flow structure development and flow energy losses may be established. A further exploration focuses on the mechanism driving the evolution and associated the momentum and energy exchanges to gain a deeper understanding of the main aerodynamic factors involved, such as shock waves, expanding waves, boundary layer under adverse pressure gradient, secondary flows and tip clearance vortices; and of the links between these factors and compressor aerodynamic performance such as efficiency, stability and pressure ratio. The research work will be supported by laboratory experiment for verification purpose, by fine numerical simulations to provide detailed flow field information and numerical experiments, and by state-of-art information processing technology for analyzing the data. The aim of the project is to identify the unknown key dynamic factors driving the vortex development in supersonic impellers and to quantify the effects of these factors on energy loss, strengthening our understanding and exploring of the flow mechanism in supersonic impellers.

超声速工业离心叶轮流道中, 多尺度涡流结构时空演变机理及对气动能量损失的影响是高性能叶轮设计和工程应用必须解决的理论瓶颈之一。本申请拟通过推导超声速叶轮内部流场信息分析的多变量动力模态分解方法, 研究流场关键流动和气动参数各阶频率模态在时间和空间上的演变规律及与流动耦合的物理诠释; 探究激波、逆压力梯度边界层、顶隙涡流和二次流等气动因素对主流涡结构时空演化、动量和能量交换规律、流动稳定性的作用机制, 明确气动因素与能量耗散之间的关联性。整体工作以精细流场信息获取-动力模态分解方法确立-能量损失要素解析为主线条展开, 以实验验证为支撑点, 以数值模拟、信息提取和理论分析为研究手段。力求从动态上挖掘超声速叶轮内部涡流运动新的气动驱动因素，量化关键气动因素对能量损失的介入度,同时确立一种有效的以超声速离心叶轮复杂涡流为物理背景的动力模态分解分析方法,增强对高转速叶轮流动机理的深入探索。

本项目基于自主开发的高精度数值模拟平台和模态解析方法，以精细流场信息获取-动力模态分解方法确立-能量损失要素解析为主线条展开研究工作。主要内容包括：新的模态分解方法（F-POD）确立；离心压气机流场动力学模态提取与解析；离心压气机变工况流场模态演化分析；离心压气机全通道旋转失速判定与信号分析方法的研究。研究以实验验证为支撑点,以数值模拟、信息提取和理论分析为研究手段，从模态分析角度挖掘超声速叶轮内部涡流运动新的气动影响因素，量化其对能量损失的介入度,同时确立一种有效的以超声速离心叶轮复杂涡流为物理背景的动力模态解析方法,增强对高转速叶轮流动机理的深入探索。研究成果有：1）基于POD方法并结合离散的傅里叶变换及其逆运算提出F-POD方法，将离心压气机复杂内流场分解成具有单一频率和确定增长率的模态结构；2）分解最高效率工况下动静部件干涉、间隙泄漏流、流动分离、尾迹涡流、激波等流动结构对应的模态，明确了各工况条件下流场的动力学模态特征及各阶模态的物理含义，为探索压气机模态特征的发展演化规律奠定了基础；3）以各阶主要模态的能量转移为依据，探索了离心压气机流场模态特征随流量变化的演化规律，揭示了压气机流动稳定性降低的模态内在驱动机制。4）在叶轮失速机理研究基础上，发展了离心压气机全通道旋转失速判定与信号分析方法。本项目研究提出了单频模态分解F-POD方法；解析了超声速离心压气机各条件下流场的动力学模态特征及物理含义；发现了离心压气机流动稳定性相关的“不稳定”模态的演化机理，并发展了离心压气机全通道旋转失速判定与信号分析方法，为离心压气机失稳研究和预测提供了新思路，对拓宽其稳定工作范围具有重要指导意义。