ERI: Experimental Investigation of Compressibility Effects on Turbulent Kinetic Energy Production in Supersonic Flows

高超音速飞行提供了彻底改变全球旅行和太空探索的潜力。实现这一目标的关键技术是为吸气式高超声速发动机开发高效的超声速燃烧室。这些燃烧室与传统燃烧室的不同之处在于其极短的停留时间，通常约为1毫秒。在如此短的时间内，燃料必须被喷射、蒸发（对于液体燃料）、分散并在燃烧发生之前与进入的空气混合到分子水平。湍流有助于分散和混合，在这一过程中至关重要。然而，对可压缩性如何影响湍流产生的理解仍然是不完整的，这减缓了高超音速飞行的发展。本计画旨在于密苏里州科技大学的马赫数3风洞中，借由直接量测紊流来研究压缩性对紊流的影响。由于湍流在混合过程中起着关键作用，了解湍流的产生以及压缩性对湍流的影响将有助于更好地理解超音速流中的混合过程和超音速燃烧室的设计。可压缩性效应--特别是对密度波动的影响--在诸如射流和剪切的非壁边界流中已经被很大程度上忽略，其与混合应用相关。最近的研究表明，即使对于超音速燃烧冲压喷气发动机燃烧室的相对较低的超音速马赫数（飞行马赫数的30-40%），可压缩性对紊流产生的影响也可以与不可压缩紊流产生的影响相比较。根据现有文献中的理论论证和有限的实验/数值数据，这种分析表明，最初为边界层开发的强雷诺类比（速度和密度波动之间的相关性）对无界超音速混合流也是有效的。本计画提出利用两点聚焦雷射差动干涉法（2-FLDI）直接量测密度与速度脉动，以实验验证强雷诺类比在超音速混合无界流中的有效性。2-FLDI是一种经过验证的低成本技术，可以对密度和速度波动进行高频、同步、非侵入式测量。流动将由一个简单的平面射流从一个挂架喷射器在马赫数3的自由流。这项工作还将通过夏令营的发展支持STEM推广，并通过支持研究生和本科生来支持高超音速技术的劳动力发展。这项工作的结果也将被纳入湍流研究生班。该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

Hypersonic flight offers the potential to revolutionize global travel and space exploration. A crucial technology for making this a reality is the development of efficient supersonic combustors for air-breathing hypersonic engines. These combustors differ from traditional ones in their extremely short residence times, typically around 1 millisecond. In such a short time, the fuel must be injected, vaporized (for liquid fuels), dispersed, and mixed to the molecular level with the incoming air before combustion can occur. Turbulence, which aids dispersion and mixing, is vital in this process. However, understanding how compressibility affects turbulence production is still incomplete, slowing down hypersonic flight development. This project aims to investigate compressibility effects on turbulence by directly measuring turbulence in the Mach 3 wind tunnel at Missouri University of Science and Technology. As turbulence plays a key role in the mixing process, understanding its production and how it is affected by compressibility would facilitate a better understanding of the mixing process in supersonic flows and the design of supersonic combustors.While turbulence production in supersonic flows has been recently investigated, compressibility effects – particularly on density fluctuations – have been largely neglected in non-wall-bounded flows such as jets and shear, which are relevant for mixing applications. Recent research indicates that even for the relatively low supersonic Mach number of a scramjet combustor (30-40% of the flight Mach), compressibility effects on turbulence production can be comparable to incompressible turbulence production. This analysis, based on theoretical arguments and limited experimental/numerical data from the available literature, indicates that the Strong Reynolds Analogy (a correlation between velocity and density fluctuations), initially developed for boundary layers, is also valid for unbounded supersonic mixing flows. This project proposes to experimentally verify the validity of the Strong Reynolds Analogy in a supersonic mixing unbounded flow by directly measuring density and velocity fluctuations utilizing two-point Focused Laser Differential Interferometry (2-FLDI). 2-FLDI is a proven low-cost technique that allows high-frequency, simultaneous, non-intrusive measurements of density and velocity fluctuations. The flow will consist of a simple planar jet from a pylon injector in a Mach 3 free stream. This work will also support STEM outreach through the development of a summer camp, and workforce development in hypersonics by supporting both graduate and undergraduate students. Findings from this work will also be incorporated into a graduate class on turbulent flows.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.