Excellence in Research: Co-axial Flow Mixing and Control using Ultra-High Frequency Actuators

创新的燃料-空气混合技术对于国防和航空运输更快、更可靠的飞机的持续发展至关重要。该项目将专注于一种新的燃油喷射方案，以增强和控制流体(燃料)与快速流动的空气的混合。该方案由两个同轴喷嘴组成：一个中心喷嘴，周围环绕一个环形喷嘴，通过它可以同时喷射空气和流体。当流体通过环形喷嘴以稳定的气流提供时，中央喷嘴以脉冲方式注入空气以增强混合。拟议的喷射系统的创新概念在于它能够以非常高的频率(每秒20,000-30,000个脉冲)为中央空气射流提供脉冲。预计流体(燃料)和高频脉冲空气将以这种方式更有效地混合。为了研究这一点，实验流体力学研究实验室将配备新的能力，利用这项研究所需的最先进的、先进的基于激光的流动诊断技术。该项目还将使用基于已建立的学习理论制定的教育计划，为工程学中代表性不足的学生提供更有效的研究经验。该项目的主要目标包括设计、开发和表征通过基础研究的主动同流喷射系统，以增强高速燃料-空气混合。该系统由位于内核的超音速驱动空气射流组成，它在稳定注入的环空流体的剪切层中提供了较大的平均和脉动速度分布，其中脉动以指定和可控的超高频发生。预计空气与同向流动流体的混合可以通过使用以这种方式为平均流量量身定做的所产生的流向涡流来改善和控制。具体任务包括通过使用平面激光诱导荧光(PLIF)测量种子颗粒密度分布和使用粒子图像测速仪(PIV)测量速度场和涡量场来定量表征混合。利用这些数据，将研究系统的扩散混合特性(例如，演化的时间尺度、界面区域的产生和混合效率)，并将其与相关的无量纲参数相关联。具体的教育活动包括有针对性地将对研究有用的高级主题注入本科水平的流体力学课程，该课程提供额外的支持，以及接触那些大学之前的情况可能会阻碍工程研究成功的学生。该奖项反映了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。

Innovative fuel-air mixing technologies are essential to the continual advancement of faster and more reliable aircrafts for both national defense and air transportation. This project will focus on a novel fuel injection scheme to enhance and control mixing of a fluid (fuel) with a fast moving air. The proposed scheme consists of two co-axial nozzles: a central nozzle surrounded by an annular one, through which air and fluid are injected simultaneously. While the fluid is supplied through the annular nozzle in a steady stream, the central nozzle injects air in a pulsed manner to enhance mixing. The innovative concept for the proposed injection system is in its ability to pulse the central air jet at very high frequencies (20,000-30,000 pulses per second). It is anticipated that the fluid (fuel) and the high frequency pulsed air will be mixed more effectively in this manner. To investigate this, an experimental fluid mechanics research lab will be equipped with new capabilities utilizing the state-of-the-art, advanced laser-based flow diagnostics that are required for this study. The project will also use educational plans that have been developed based upon established learning theories to provide more effective research experience to underrepresented students in engineering.Major goals of this project include design, development, and characterization through fundamental studies of an active co-flow injection system for enhanced fuel-air mixing at high speeds. The proposed system consists of a supersonic actuation air jet at the inner core that provides large mean and fluctuating velocity profiles in the shear layer of a steadily-injected annular fluid, where the fluctuations occur at a designated and controllable ultra-high frequency. It is expected that the mixing of air with the co-flowing fluid can be improved and controlled using resulting stream-wise vortices that are tailored to the mean flow in this manner. The specific tasks include quantitative characterization of mixing through measurement of seed particle density distribution using planar laser-induced florescence (PLIF) and velocity and vorticity field measurement using particle image velocimetry (PIV). Using these data, the diffusive mixing characteristics of the system (e.g., the timescales of evolution, interfacial area generation and mixing efficiency) will be studied and correlated to the relevant non-dimensional parameters involved. Specific educational activities include targeted infusion of advanced topics useful in research to an undergraduate level fluid mechanics course which provides additional support, and access to students whose pre-college situations may otherwise preclude success in engineering research.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.