周向非均匀人流/出流条件下无叶扩压器敏感性分析

Sensitivity Analysis of the Vaneless Diffuser Flow under Circumferential Asymmetric Inflow/Outflow Condition

不稳定流动是高速离心压缩机内部流动的本质特征,其诱发机制往往受到关键结构参数与边界处流动条件的影响.本文以带有无叶扩压器的离心压缩机为研究对象,基于线性的全局稳定性理论,同时考虑涡黏性与分子黏性的作用,建立了基于无叶扩压器r-θ平面的二维稳定性分析方法,获得了流动失稳的直接全局模态;然后基于伴随方法获得了对应最不稳定特征值的伴随全局模态,结合直接与伴随模态构建了流场特征值的结构敏感性。最后考虑了射流-尾流流动结构,以及蜗壳非对称几何结构的影响,分别对周向非均匀入流/出流条件下的无叶扩压器流动进行了稳定性与敏感性分析。分析结果表明机匣侧出口回流对无叶扩压器全局稳定性具有关键作用;在无蜗壳时,射流-尾流结构对于全局稳定性的影响主要体现在失速团个数,而对失稳机理的影响较小;蜗壳的非对称结构导致流场重新分布,在距离蜗舌顺时针90°~135°位置出口壁面回流与入口回流相互作用,是诱发失稳扰动产生的主要因素。

Unsteady flow is often observed in high-speed centrifugal compressor.The physical mechanism for it is often the combining effect of critical geometric parameters and boundary conditions.The vaneless diffuser flow in a centrifugal compressor is studied in the present work.Based on the global linear stability theory,a 2 D stability analysis method is established at the r-θplane considering both the turbulent viscosity and molecular viscosity.The direct modes are obtained.Then,the adjoint modes are also obtained based on adjoint method.And the structural sensitivity is derived based on both the direct and adjoint modes.Finally,the influence of jet-wake flow and volute are studied.The results indicates that the reverse flow at the flow at the shroud side is crucial for the stability of vaneless diffuser.The influence of jet-wake flow mainly lies at the stall cell number rather than the physical explanation of stall.The asymmetric structure of volute results into redistribution of flow field.The interaction between the reverse flow and inflow wake flow at the circumferential position 90°~135°away from the volute tongue is the main cause for the occurrence of stall.