Filtered Rayleigh scattering for multi-parameter fluid flow analysis

在航空航天试验设施中，例如风洞、燃气涡轮压气机和燃烧实验，有必要获得这些实验中流体流动的数据，以提高性能，从而减少有害排放和噪音，并更好地了解基本的流体过程。所需的数据包括密度、压力、温度和流速。目前可用的技术允许测量这些流动特性，但有局限性：可能需要使用多种技术来测量不同的特性。这些技术可能仅限于进行单点测量，需要昂贵且耗时的扫描机制来“绘制”流动。此外，一些测量流速的技术需要在流动中加入小的“种子”颗粒，如果这些种子颗粒不能准确地跟随流动，可能会导致不准确的速度测量。此外，在某些应用中，向流动中添加“种子”颗粒也会受到限制，导致光学窗口被污染，限制了测量时间并增加了技术费用。滤波瑞利散射（FRS）是一种很有前途的光学技术，可以同时测量流体的多种特性（温度、压力、密度和速度）。测量是非侵入性的，因此流不会因测量而改变。测量可以在单个点上进行，或者更重要的是在流中的激光光片所定义的平面上的多个点上进行。在FRS中，流动特性是通过测量瑞利散射光来确定的。这是由气体分子本身散射出来的光，因此不需要“种子”粒子。当光从气体分子中散射出来时，它的光谱会因气体的性质而改变。气体的密度可由散射强度求得。温度可以通过散射光谱的宽度来确定，速度可以通过频率相对于激光光频的偏移来确定。这两种效应都是由于多普勒频移，流速引起光照频率的偏移，而温度由于分子热运动的多普勒频移而使光谱变宽。最后，压强可以通过观察光谱的形状来确定。本课题的研究方向是发展FRS仪器作为一种多参数测量技术，应用于风洞、燃气轮机压气机和燃烧设施。将对所建造的仪器进行试验，但不是进行持续的测量运动，而是向最终用户和工业界传播该技术的能力和局限性，以供以后的合作方案使用。

In aerospace test facilities, for example wind tunnels, gas turbine compressors and combustion experiments, it is necessary to obtain data about the fluid flows in these experiments to improve performance thus reducing harmful emissions and noise and to gain a better understanding of the fundamental fluid processes. The data required includes the density, pressure, temperature and velocity of the flow. Presently available techniques allow the measurement of these flow properties but have limitations: multiple techniques may need to be used to measure the different properties. The techniques may be limited to making single point measurements, requiring an expensive and time-consuming scanning mechanism to 'map' the flow. Additionally some of the techniques for measuring flow velocity require small 'seed' particles to be added to the flow which may result in inaccurate velocity measurements if these seed particles do not follow the flow accurately. Also, the addition of 'seed' particles to the flow is limiting in some applications, causing optical windows to become fouled limiting the measurement time and increasing the expense of the technique.Filtered Rayleigh scattering (FRS) is a promising optical technique that can potentially measure multiple properties (temperature, pressure, density and velocity) of the flow simultaneously. The measurements are made non-intrusively, so the flow is not changed by the measurement. Measurements can be made at a single point, or more significantly at multiple points over a plane defined by the laser light sheet in the flow. In FRS the properties of the flow are determined by measuring the Rayleigh scattered light. This is light scattered from the molecules of the gas itself, and as such no 'seed' particles are required. When the light is scattered from the gas molecules it will have its spectrum altered by the properties of the gas. The density of the gas can be found from the scattered intensity. The temperature can be found from the width of the scattered spectrum and the velocity from the shift in frequency compared to the optical frequency of the laser. Both of these effects are due to the Doppler shift, with the flow velocity causing a shift from the illumination frequency and the temperature provide a widening of the spectrum due to the Doppler shifts from the thermal motion of the molecules. Finally the pressure can be found by looking at the shape of the spectrum.The research proposed is the development of FRS instrumentation as a multi-parameter measurement technique for application in wind tunnels, gas turbine compressor and combustion facilities. Trials of the instruments constructed will be made, but not sustained measurement campaigns, rather the capabilities and limitations of the technique will be disseminated to end-users and industry for subsequent collaborative programmes.