离心叶轮失速涡结构演化与耦合特征研究

Evolution and coupling characteristics of stall vortex structures in a centrifugal impeller

关键词:  离心叶轮  旋转失速  龙卷风涡结构  叶顶泄漏涡  耦合演化

Key words:  Centrifugal impeller  Rotating stall  Tornado-vortex structure  Tip leakage vortex  Coupling evolution

摘要:

为深入解析离心压气机旋转失速的涡流耦合演化机理，基于Eckardt离心叶轮全通道非定常数值模拟数据，利用涡系识别法和傅里叶频谱分析等方法研究了失速工况下叶轮中关键涡流结构的空间分布特征及非定常演化规律，发现失速流场同时存在两类涡流结构：叶片前缘龙卷风涡和叶顶泄漏涡，两类流动结构交替演化、相互作用，形成了以63%叶轮转速周向传播的失速团，促使离心叶轮失速。具体体现为：叶顶泄漏涡形成并发展，裹挟、牵引叶片前缘分离涡从叶顶开始剥离，直至完全从叶片吸力面脱落。脱落后的分离涡沿周向运动，受到叶片阻挡产生溢流，该溢流流体在叶片压力面与吸力面横向压差的作用下演变为龙卷风涡，该龙卷风涡在周向运动过程中被叶片“截断”为两段而后向下游扩散并逐渐耗散消失。之后新的叶顶泄漏涡又逐渐兴起，形成下一个涡流演化周期。两种涡结构此消彼长、周而复始，共同构成了失速演化特征。

Abstract:

To deeply analyze the vortexes coupling evolution mechanisms of centrifugal compressor rotating stall， on the basis of the full-passage unsteady simulation data of the Eckardt centrifugal impeller， the spatial distribution characteristics and the unsteady evolution regularities of the key flow structures of the impeller in the stall condition were studied by the vortex identification method and the Fourier spectrum analysis. There were two types of the vortex structures in the stall flow field at the same time： the tornado-vortex on the leading edge of the blade and the tip leakage vortex. The two types of flow structures alternately evolve and interact， forming stall cells that propagate at about 63% of the impeller speed along circumference， prompting the centrifugal impeller to stall. Specifically， the tip leakage vortex is firstly formed and developed. The leading edge separation vortex is entrained and dragged by the tip leakage vortex to gradually shed from the blade tip region， resulting in a complete vortex shedding from the blade suction side. Then， the separation vortex after shedding moves in the circumferential direction， and is blocked by the blade， leading to the generation of leading edge spillage. The spilled fluid evolves into a tornado vortex under the action of the lateral pressure difference between the blade pressure side and the suction side. It is truncated into two segments by the blade during the circumferential motion， and then diffuses downstream and gradually dissipates. After that， the new tip leakage vortex gradually emerges， forming the next vortex evolution cycle. The two kinds of vortex structures change and go back and forth， which together constitute the characteristics of stall evolution.