Control of Instability Transition in Transverse Jets

射流垂直注入横流，或横向射流，存在于自然界和广泛的工程应用。例如，横向射流用于控制燃料-空气混合以及飞行器的燃气涡轮机发动机以及固定发电厂中的涡轮机叶片的冷却。这种喷射器也用于液体火箭发动机预燃室和环境控制系统中的流体喷射。火山羽流在多风的环境中也可能表现得像横向喷流。控制和优化横向射流行为可以提高燃油效率，控制车辆性能，并潜在地减少对环境的影响，所有这些都是重要的经济，能源和国家安全目标。最近的实验研究已经证明了主动控制横向射流或控制紧邻射流外部的流动的价值，以便改善一系列流动状态和应用的性能。在这个项目中，拟议的实验研究旨在更详细地关注横向射流不稳定性的基本物理学。这包括研究它们的动态特性，它们是如何产生的，以及如何以稳健的方式主动控制它们。拟议研究的更广泛影响将超越实际应用和研究生水平的研究。它将包括本科生研究培训，社区推广，并为当地高中和社区大学的学生和其他大学的潜在本科生提供暑期实验室体验。 拟议的实验研究活动将检查剪切层的不稳定性和不对称性，自然形成的横向射流流场，以及如何不同的激励方法可以控制射流行为适合不同类别的应用。 除了基本探索的单一，湍流产生的横向射流，它建议检查一个替代配置，同轴射流横流。 这将确定一种新的模式的效果，通过创建逆流剪切使用吸入或吹在同轴射流的外环形部分的剪切层不稳定性的控制。 这些研究还将建立在最近发现的动态锁定，准周期性，并与适当的正交分解从激光为基础的成像的单横向射流模式的规律。 预计将通过与巴西联邦弗鲁米嫩塞大学（UFF）的研究人员进行国际合作，进行涉及横向射流剪切层动力学的线性稳定性理论的相应研究。 拟议的研究有可能产生前所未有的理解和识别的控制方法，为未来的创新，在推进和能源发电systems.This奖项反映了NSF的法定使命，并已被认为是值得的支持，通过评估使用基金会的智力价值和更广泛的影响审查标准。

Jets injected perpendicularly into a cross-stream, or transverse jets, exist both in nature and in a wide range of engineering applications. For example, transverse jets are used to control fuel-air mixing and cooling of turbine blades in gas turbine engines for aircraft as well as in stationary power plants. Such jets are also used for fluid injection in liquid rocket engine pre-burners and in environmental control systems. A volcanic plume may also behave like a transverse jet in a windy environment. Controlling and optimizing transverse jet behavior can improve fuel efficiency, control vehicle performance, and potentially reduce environmental impact, all of which are important economic, energy and national security goals. Recent experimental studies have demonstrated the value of actively controlling transverse jets, or controlling the flow immediately exterior to the jets, in order to improve performance for a range of flow regimes and applications. The proposed experimental studies in this project are designed to focus, in greater detail, on the fundamental physics of transverse jet instabilities. This include studying their dynamical character, how they arise, and hence how they may be actively controlled in a robust manner. The broader impacts of the proposed studies will expand beyond practical applications and graduate level research. It will include undergraduate research training, community outreach, and summer laboratory experiences for local high school and community college students and potentially undergraduates at other universities. The proposed experimental research activities will examine shear layer instabilities and asymmetries that naturally form in the transverse jet flow field, and how different approaches for excitation can control jet behavior tailored to different classes of applications. In addition to fundamental exploration for the single, nozzle-generated transverse jet, it is proposed to examine an alternative configuration, a coaxial jet in crossflow. This will determine the effects of a new modality for control of shear layer instabilities via creation of counter-current shear using suction or blowing in the outer annular section of the coaxial jet. The studies will also build on recent discoveries of dynamical lock-in, quasi-periodicity, and regular patterns in modes associated with proper orthogonal decomposition from laser-based imaging of the single transverse jet. Corresponding studies involving linear stability theory applied to transverse jet shear layer dynamics are expected to be pursued via an international collaboration with researchers at the Universidade Federal Fluminense (UFF) in Brazil. The proposed studies have the potential to yield unprecedented understanding and identification of control methodologies for future innovations in propulsion and energy generation systems.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.