Control of Instability Transition in Transverse Jets

垂直喷射到横流中的射流，或称横向射流，在自然界和广泛的工程应用中都存在。例如，在飞机燃气轮机发动机和固定发电厂中，横向射流被用来控制涡轮叶片的燃料-空气混合和冷却。这种喷嘴还用于液体火箭发动机预燃器和环境控制系统中的流体喷射。在有风的环境中，火山羽流也可能表现得像横向急流。控制和优化横向喷射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。最近的实验研究表明，为了改善各种流型和应用的性能，主动控制横向射流或控制射流外部的流动是有价值的。该项目中拟议的实验研究旨在更详细地关注横向喷流不稳定性的基本物理。这包括研究它们的动力学特征，它们是如何产生的，从而研究它们如何以一种强有力的方式被积极控制。拟议研究的更广泛影响将超出实际应用和研究生水平的研究。它将包括为当地高中和社区学院的学生以及其他大学的潜在本科生提供的本科研究培训、社区推广和暑期实验室体验。拟议的实验研究活动将检查横向喷流场中自然形成的剪切层不稳定性和不对称性，以及不同的激励方法如何控制适合不同应用类别的喷流行为。除了对单一喷嘴产生的横向射流的基本探索外，还建议研究另一种可选构型，即横流中的同轴射流。这将决定一种控制剪切层不稳定性的新模式的效果，该模式通过在同轴射流的外环区段利用吸力或吹气产生逆流剪切。这些研究还将建立在最近发现的动态锁定、准周期和规则模式的基础上，这些模式与基于激光的单一横向喷流成像的适当正交分解相关。预计将通过与巴西联邦弗卢米嫩塞大学(UFF)的研究人员开展国际合作，开展将线性稳定性理论应用于横向喷流剪切层动力学的相应研究。拟议的研究有可能对未来推进和能源发电系统创新的控制方法产生前所未有的理解和识别。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.