Examination of Pressure and Velocity Fields and Their Relationships to Radiated Noise in a Jet

湍流产生的噪声是一种基本的流动现象，具有广泛的实际应用，包括交通工具。一个具体的例子是飞机喷流产生的湍流所产生的噪声。喷气式飞机的噪音可能是飞机起飞时的主要噪音，也可能是航班数量、一天中的时间和飞机离开机场的飞行路径的限制因素，因为法规关注的是机场附近居民的生活质量（可接受的噪音污染）。在过去的许多年里，喷气噪声的显著降低主要是通过增加涡轮风扇发动机的风扇流量来实现的。通过引入波纹喷嘴来改变射流剪切层中的混合，在射流降噪方面取得了其他进展。然而，总的来说，仍然缺乏对湍流中导致噪声产生的潜在物理的基本理解，因此如何以有效的方式减少它。所提出的实验努力旨在利用新颖的实验仪器和分析技术识别轴对称射流自由剪切流湍流中产生噪声的事件。虽然射流是本研究的重点，但对压力场和速度场之间关系的基本理解，以及它们与噪声产生的关系，将直接影响许多其他存在自由剪切流产生噪声的应用。该项目将为高中生提供在实验室工作的机会，并为暑期项目开发噪音和传感模块。湍流中自由剪切层产生的噪声在工程应用中是普遍存在的。在这项工作中，一种新型的MEMS传感器将被开发出来，可以测量静压波动，而流量干扰最小。该传感器的测量将与粒子图像测速法的平面速度测量相结合，以深入了解射流剪切层中湍流运动产生的噪声。数据分析将包括流入压力的单点和多点测量，以检查流中波包事件的时空性质。此外，同步速度和波动静压测量将通过直接分析以及压力-应变率相关性的检查来检查与压力场相关的流动事件。对静压力波动条件下随时间变化的速度事件的随机估计技术将用于阐明与流动压力事件相关的大尺度湍流特征。进一步的分析将涉及流中压力事件与远场噪声之间的因果关系研究。

Noise production from turbulent flow represents a fundamental flow phenomena that has wide reaching practical applications including transportation vehicles. One specific example is the noise produced by the turbulent flow exiting from the jet of an aircraft. Jet noise can be the dominant aircraft noise during takeoff and can be a limiting factor for the number of flights, the time of day, and the flight path for aircraft leaving the airport because of regulations focused on quality of life (acceptable noise pollution) for residence adjacent to an airport. Significant reductions in jet noise over the past many years has primarily been achieved by increasing the fan flow in turbo-fan engines. Other advances in jet noise reduction have been achieved by the introduction of corrugated nozzles to alter the mixing in the jet shear layer. In general, however, there is still a lack of a fundamental understanding of the underlying physics in the turbulent flow that leads to noise production and hence how to reduce it in an efficient fashion. The proposed experimental effort is designed to identify noise producing events within the turbulence of the free shear flow of an axisymmetric jet using novel experimental instrumentation and analysis techniques. Although jet flows are the focus of this investigation, the fundamental understanding of relationships between the pressure and velocity fields and how they relate to noise generation should directly impact many other applications where there is free shear flow generated noise. The project will provide high school students an opportunity to work in the laboratory and to develop noise and sensing modules for a summer program.The presence of noise generated by free shear layers in turbulent flows is ubiquitous throughout engineering applications. In this effort a new and novel MEMS sensor will be developed that can measure static pressure fluctuations, with minimal flow disturbances. Measurements from this sensor will be coupled with planar velocity measurements from particle image velocimetry to shed insight into the noise produced by turbulent motions in a jet shear layer. The analysis of the data will involve single and multi-point measurements of the inflow pressures to examine the spatio-temporal nature of wave-packet events in the flow. Additionally, synchronous velocity and fluctuating static pressure measurements will be examined to correlate flow events associated with pressure field through direct analysis along with an examination of the pressure-strain rate correlations. Stochastic estimation techniques of the time-dependent velocity events conditioned to the static pressure fluctuations will be used to elucidate the large scale turbulent flow features associated with the flow pressure events. Further analysis will involve causality studies relating the pressure events in the flow to the far field noise.