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

预测和控制两种流体混合的能力在许多工程应用中是重要的，例如在燃烧中的燃料和氧化剂之间。混合两种流体也会产生不希望的噪音，例如喷气发动机的排气与周围空气结合产生的噪音。一个特别值得关注的领域是在两种不同速度的气流之间形成的剪切层中发生的湍流混合。混合控制了流体性质在该层上的传输，并导致了剪切层内产生的噪声。混合特性和声音产生随着两流之间速度差的增大而变化。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。对某个量（如温度）的瞬时测量可以深入了解发生在剪切层中的湍流混合，因为混合控制着该量的波动。激光感应光栅（LIG）是一种获取流场特定位置瞬时温度的非侵入式方法。本项目旨在提高LIG的信号强度，将其应用于更广泛的流动，并将这种新的LIG技术应用于亚音速和超音速射流，以便在两种流动之间的可变速度差的剪切层中获得温度。该项目的具体目标是1)确定速度差对剪切层温度波动的影响，2)强调平均温度和波动温度对流动结构的依赖，以及3)深入了解有助于声音产生和混合的热力学。该研究项目的智力价值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。可压缩性是衡量两种流动之间速度差的一种指标，它的影响是一个具有实际重要性的问题，人们已经研究了几十年；然而，对理解这个问题至关重要的涨落特性的测量仍然难以捉摸。随着LIG技术的应用范围将扩大到其他高速流动，未来还可以在其他重要流动中获取温度，如平面剪切层、基流、喷射流等。这项研究的更广泛的影响包括更好地理解控制混音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被记录在案，但其潜在的物理原因尚未完全确定。提高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噪音产生控制等应用的理解将是至关重要的。此外，作为RUI项目，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夏季被雇用来执行实验并展示结果，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，为工科本科学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.