航空发动机短舱声衬表面剪切流与声波相互作用研究

Effective and accurate liner impedance models and sound propagation calculations in lined ducts are crucial to aero-engine liner design. However, the complexity of flow-acoustic interaction occurring near the surface of a liner makes it difficult to develop these models. Recent theoretical and experimental studies have revealed that the widely-used uniform flow assumption leads to problems both in impedance prediction and in sound propagation calculation, due to its insufficiency in modeling flow-acoustic interaction. Therefore, the influence of shear flow inside the boundary layer on liner impedance and sound propagation in lined ducts will be carefully studied in this project. To this end, we will develop two types of models for the vortex-sound interaction occurring at the liners. The first is the discrete vortex model which describes the vortex by discrete particles. The second one is based on multimodal method, where the vortical part is modeled as hydrodynamic waves. Also, experiments will be carried out to verify these models. It is expected that this project leads to new knowledge of vortex-sound theory, provides more accurate tools for liner design, and points out the limits of the current models based on uniform flow assumption.

短舱声衬对航空发动机风扇噪声控制至关重要，其理论研究主要包括两方面：声阻抗预测与装有声衬管道内声传播计算。短舱内“有流动”环境极大地增加了这两方面研究难度，理论和实验研究均表明，现有基于声衬表面均匀流假设的模型存在诸多问题。究其原因，均匀流模型不能充分刻画声衬表面复杂流动-声波相互作用。因此，本项目拟在对流动的描述上更进一步，即在声衬表面流动边界层内考虑更接近真实情况的剪切流，来细致地研究边界层内剪切流对声衬处涡声相互作用、声衬阻抗、以及装有声衬管道内声传播的影响。为此，我们将发展两类理论模型，将流场中涡描述为涡粒子的离散涡模型与将流场中涡相关部分描述为流体动力学波的多模态模型，并配合验证实验。期望一方面在“涡声相互作用”基础科学问题范畴内有新的发现，另一方面提供一套包括边界层内剪切流影响的短舱声衬设计工具，并给出已有的基于均匀流假设模型的适用范围。

本项目发展了两个描述涡声相互作用物理过程的半解析/半数值模型：离散涡模型与多模态模型。然后，基于所发展模型，对穿孔板-空腔结构（非局域声衬）、空腔-流管结构的涡声相互作用机理进行了细致研究。不但研究声衬吸声与声衬阻抗，而且研究了声放大、自发声与流动自激振荡问题。为研究这里涡声相互作用与流动不稳定性关系，不同于当前研究流动全局模态的普遍做法，本项目发展了以行波模态构造全局模态的计算模型，统一分析：全局/行波模态、全局/局部对流不稳定性。首次揭示出“涡声共振”机制，并得到全局不稳定性的一种判据：实频反馈循环增益是否大于1决定流动是否全局不稳定。本项目揭示并细致研究了涡声相互作用、共振、流动不稳定性的内在关联，厘清如何关联，为理解非定常流动与声波复杂耦合的内在机理提供了一个新视角；全面阐释涡声相互作用物理驱动机制，有助于形成航空等领域流动振荡抑制、流动噪声控制的新思路。项目资助下,发表SCI论文3篇（其中2篇发表于流体力学著名期刊Journal of Fluid Mechanics）。