RUI: Nonintrusive Temperature Measurements in Compressible, Axisymmetric Shear Layers Using Two-Photon Stimulated Raman Excitation of Laser-Induced Gratings

1232624Kuehner预测和控制两种流体之间混合的能力在许多工程应用中都很重要，例如燃烧中燃料和氧化剂之间的混合。混合两种流体也会产生不需要的噪音，例如，与喷气发动机排气和周围空气相结合的噪音。一个特别值得关注的领域是在两种不同速度的流动之间形成的剪切层中发生的湍流混合。混合控制着流体性质在该层中的传输，并导致剪切层内产生的噪声。混合特性和声音产生随着两流之间的速度差的增加而改变。通过了解剪切层的动力学，可以更好地预测湍流混合和声音产生，并在实际应用中进行潜在的修正。对温度等量的瞬时测量可以洞察剪切层中发生的湍流混合，因为混合控制着这样一个量的波动。激光诱导光栅(LIG)是一种非侵入性的方法，用于获取流场中特定位置的瞬时温度。该项目旨在提高LIG的信号强度，将其应用到更广泛的流动中，并将这一新的LIG技术应用于亚音速和超音速喷流，以便在两种流动之间的不同速度差的情况下，获得剪切层中的温度。这个项目的具体目标是1)确定速度差对剪切层温度波动的影响，2)突出平均和波动温度对流动结构的依赖，以及3)洞察有助于声音产生和混合的热力学。研究项目的智力优势包括对高速剪切层中发生的湍流混合的改进知识和LIG技术的扩展能力。可压缩性的影响是一个几十年来一直研究的具有实际意义的问题，它是衡量两种流动之间速度差异的指标；然而，对了解这一问题至关重要的波动性质的测量仍然难以捉摸。由于LIG技术的应用将扩展到其他高速流动，未来可以在其他重要流动中获得温度，如平面剪切层、基流和喷注流动。这项研究的更广泛影响包括更好地理解控制混合和声音产生的可压缩湍流动力学。可压缩性对湍流的影响已经被记录在案，但潜在的物理原因还没有完全确定。更好的理解将对超燃冲压发动机的超音速燃油喷射、火箭推进和商用飞机的噪音控制等应用至关重要。此外，作为RUI的一个项目，这项调查将在一所小型的文科本科大学进行。本科生研究助理将在学年和暑假期间受聘进行实验并展示结果，为不同背景的学生提供宝贵的经验。该实验装置将用于物理与工程系流体力学实验室，为工科本科生提供研究和学习经验。

1232624KuehnerThe ability to predict and control mixing between two fluids is important in many engineering applications, such as between the fuel and oxidizer in combustion. Mixing two fluids can also generate undesirable noise, for example the noise associated with the exhaust of a jet engine combining with the surrounding air. One area of particular concern is the turbulent mixing that occurs in the shear layer that forms between flows of two different speeds. The mixing governs the transport of fluid properties across that layer and contributes to the noise generated within the shear layer. The mixing characteristics and sound generation change as the difference in speeds between the two flows increases. By understanding the dynamics of the shear layer, the turbulent mixing and sound generation can be better predicted and potentially modified in practical applications. Instantaneous measurements of a quantity such as temperature can provide insight into the turbulent mixing that occurs in the shear layer, as mixing governs the fluctuations in such a quantity. Laser-induced gratings (LIG) is a nonintrusive method for acquiring instantaneous temperature at specific locations within the flow field. This project aims to improve the signal strength of LIG to expand its application to a wider range of flows and to apply this new LIG technique to subsonic and supersonic jet flows so that temperature can be acquired in shear layers for variable difference in speed between the two flows. The specific objectives for this project are to 1) determine the effects of the speed difference on temperature fluctuations in the shear layers, 2) highlight the dependence of mean and fluctuating temperature on flow structure, and 3) provide insight into the thermodynamics that contribute to sound generation and mixing.The intellectual merit of the research project encompasses an improved knowledge of the turbulent mixing that occurs in high-speed shear layers and an expanded capability of the LIG technique. The effect of compressibility, a measure of the speed difference between the flows, is a problem of practical importance that has been studied for several decades; however, measurements of the fluctuation properties crucial to understanding the problem have remained elusive. As the application of the LIG technique will be broadened to other high-speed flows, temperature can be acquired in other important flows in the future, such as planar shear layers, base flows, and jet injection flows.The broader impacts of this study include a better understanding of the compressible, turbulent dynamics that govern mixing and sound production. The effects of compressibility on turbulence have been documented, but the underlying physical causes have yet to be fully defined. Improved understanding will be critical to applications such as supersonic fuel injection in scramjet engines, rocket propulsion, and control of noise production in commercial aircraft. Moreover, as an RUI project, the investigation will occur at a small, liberal-arts, undergraduate university. Undergraduate research assistants will be employed during the academic year and over the summers to perform the experiments and present the results, providing invaluable experience for students of many backgrounds. The experimental apparatus will be used in the fluid-mechanics laboratory in the Physics and Engineering Department, providing research and learning experience for the undergraduate engineering majors.