流动不稳定性对迷宫密封效率的影响

The Influence of Flow Instability on Labyrinth Seal Efficiency

采用TVD格式求解非定常可压缩Navier－Stokes方程，数值研究恒定压比作用下不同空腔深宽比H／W和倾向6的迷宫密封内部流动。计算了3种矩形空腔模型（H／W=0．1，0．3，0．5，θ=0°）和两种倾斜空腔模型（θ=45°，-45°，H／W=0．5）的流动，结果展示了后倾空腔模型（θ=-45°）的稳态流动结构和其余4种模型的流动振荡及出口泄漏量的波动。通过分析涡运动与涡合并、分离泡生成与迁移、射流弯曲和冲击空腔前壁及其相关效应等流动现象的内在联系，揭示了局部不稳定效应增加能耗减小泄漏的作用机制。计算表明，矩形空腔模型中H／W=0．3的不稳定效应最强，前倾空腔比矩形和后倾空腔具有更强的不稳定效应；密封效率的变化趋势与此相同，与实验结果相符。最后，提出总体流动结构基本稳定和局部流动结构不稳定的迷宫密封流体动力学机理，指出不稳定效应的强弱差异是造成不同结构参数密封效果优劣的重要原因。

The labyrinth channel flows driven by constant pressure ratio are numerically studied under various depth to width ratios,H/W, and cavity inclinations, θ. The time-dependent compressible Navier-stokes equations are solved by a high-order finite volume algorithm based on TVD scheme. Calculations for 3 models of rectangular cavity (H/W= 0. 1, 0. 3, 0. 5, respectively, and θ= 0°) and 2 models of inclined cavity (θ- 45°, - 45°,respectively, and H/W = 0. 5) are performed. The oscillation of flow structures and fluctuation of leakage rate at cavity exit, except for the steady flow for backward-inclined cavity (θ= - 45°), are observed. With the analysis of the unsteady flow physics including vortex formation, convection and merging, separation bubble formation and migration, and jet bending,impact and its related phenomena, the mechanism of the effect of unsteady local structures on increase of energy dissipation and decrease of leakage is revealed. It is indicated that the effect of unsteady local structures for model of H/W= 0. 3 has the highest intensity in all of the rectangular cavity models, and forward-inclined cavity(θ= 45°) has a higher intensity of unsteady effect than rectangular (θ- 0°) and backward-inclined (θ= - 45°) cavity models. The seal efficiency display the same trend as unsteady effect and agree fairly well with the experimental data. Finally, a new concept about fluid mechanics of labyrinth seal, which the labyrinth seal flow is a dynamic equilibrium between the essential steady general structures and unsteady local structures, and the differences in intensity of unsteady effect is mainly responsible for the differences in seal efficiency for various labyrinth geometries, is put forward.