Laser optical measurements of the acoustic particle velocity at bias flow liners with grazing flow

激光光学测量偏流衬管处掠流声粒子速度

• 批准号: 196686122
• 负责人: Professor Dr.-Ing. Jürgen W. Czarske
• 金额: --
• 依托单位: Bremer Institut für Messtechnik, Automatisierung und Qualitätswissenschaft (BIMAQ)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2011
• 资助国家: 德国
• 起止时间: 2010-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/196686122?language=en
• 关键词: Laser; optical; measurements; acoustic; particle

For a stable and low-noise operation of a modern jet engine, especially in case of lean combustion, highly efficient sound attenuators with bias flow (bias flow liners) are needed, since on the one hand, the combustion chamber of such an engine tends to suffer from combustion oscillations, on the other hand less air mass flow is available for the damping. However, the optimization of the damping efficiency of these bias flow liners requires a deeper understanding of the physical damping mechanisms. The damping performance of such a liner is determined by complex phenomena of interaction between the incident sound field and the flow field. Therefore, the goal of the research project is to reach a better understanding of these phenomena. For this end, an energy balance of the transfer from the sound field to the flow field is aspired. On the one hand, this necessitates three-dimensional measurements of the acoustic particle velocity and the flow velocity field. To achieve this, the Doppler global velocimetry with sinusoidal laser frequency modulation (FM-DGV) will be applied, which has been proven suitable already during the first funding period. However, the current FM-DGV system has to be extended for volumetric measurements at first. In doing so, it is planned to integrate a high speed camera to increase the efficiency, which represents an alternative to the detector array used so far. Moreover, it is intended to accelerate the signal processing by parallelization. On the other hand, the challenge concerning the evaluation of the velocity fields measured above the bias flow liner is to separate the acoustically induced hydrodynamic oscillations from the primary sound and flow field. For this purpose, different analysis and separation methods (e.g. Helmholtz Hodge decomposition, spectral analysis and wavenumber filtering) have to be tested and to be applied. Here, the aim is to develop the energy transfer from the acoustic to the flow field based on the amount of energy of the separated fields. This transfer will be proven by a comparison with the sound energy dissipation of the liner obtained by microphone measurements. As a last step of this second funding period, the qualified measurement techniques and analysis methodology are applied at a simplified bias flow liner at the specifically built DUCT-R (duct acoustic test rig - rectangular cross section). Using the measured velocity field data, the energy transfer from the sound field to the flow field can be balanced which enables gaining new insights concerning the physical damping mechanisms at bias flow liners.

为了现代喷气发动机的稳定和低噪音运行，特别是在稀薄燃烧的情况下，需要具有偏流的高效消音器（偏流衬套），因为一方面，这种发动机的燃烧室往往会产生噪音。另一方面，为了遭受燃烧振荡，可用于阻尼的空气质量流量较少。然而，这些偏流衬套的阻尼效率的优化需要对物理阻尼机制有更深入的了解。这种衬垫的阻尼性能是由入射声场和流场之间相互作用的复杂现象决定的。因此，该研究项目的目标是更好地理解这些现象。为此，需要从声场到流场的传递达到能量平衡。一方面，这需要对声粒子速度和流速场进行三维测量。为了实现这一目标，将应用采用正弦激光频率调制的多普勒全球测速仪（FM-DGV），该技术在第一个资助期间已被证明是合适的。然而，当前的 FM-DGV 系统必须首先扩展到体积测量。为此，计划集成高速摄像机以提高效率，这是迄今为止使用的探测器阵列的替代方案。此外，它旨在通过并行化来加速信号处理。另一方面，评估在偏流衬管上方测量的速度场的挑战是将声引起的流体动力振荡与主要声音和流场分开。为此，必须测试并应用不同的分析和分离方法（例如亥姆霍兹霍奇分解、光谱分析和波数滤波）。这里的目标是根据分离场的能量大小开发从声场到流场的能量转移。这种传递将通过与麦克风测量获得的内衬的声能耗散进行比较来证明。作为第二个资助期的最后一步，合格的测量技术和分析方法应用于专门建造的 DUCT-R（管道声学测试台 - 矩形横截面）的简化偏流衬里。使用测量的速度场数据，可以平衡从声场到流场的能量传递，这使得能够获得关于偏流衬里的物理阻尼机制的新见解。