RESEARCH INITIATION AWARD: TAILORING JET INSTABILITIES USING ULTRASONIC MICROACTUATORS

研究启动奖为历史悠久的黑人学院和大学的初级和职业生涯中期教师提供支持，这些教师正在建立新的研究计划或重新定向和重建现有的研究计划。预计该奖项有助于进一步提高教师的研究能力和有效性，改善其所在机构的研究和教学，并让本科生参与研究经验。授予塔斯基吉大学的奖项可能会在许多领域产生更广泛的影响。该项目的目标是利用一种名为共振增强型微射流(REM)的超高频微流控技术来研究射流不稳定性的基本特征及其潜在的变化。利用REM进行不稳定性修正，在增强超音速空燃混合和控制喷流噪声方面具有潜在的应用前景。本科生将获得实验流体力学的研究经验。将开设一门实验流体力学课程，包括数字数据采集、随机数据分析和气体动力学。该项目包括超高频(20 kHz以上)REM的设计和制造，以及它们对自由和横流结构空气射流剪切层动力学的相互作用和影响的研究。将使用非稳定侵入性探头以及非侵入性技术(如基于激光的微纹影和平面散射成像)来研究射流特性。所提出的微驱动方案有望改变射流的固有不稳定性，激励最不稳定的模式，并产生高频三维涡旋，以增强卷吸和扩散。本文提出的激励器可以产生高达50 kHz的高动量脉冲扰动，在横流射流中每隔20微秒产生一次不稳定。由于这样的时间尺度非常接近高速燃烧室的混合时间，这种方法有望潜在地增强超音速流动中的空气-燃料混合。这种特制射流流场的基础研究将有助于设计具有更好的空燃混合和火焰稳定性的高速燃烧室。

Research Initiation Awards provide support for junior and mid-career faculty at Historically Black Colleges and Universities who are building new research programs or redirecting and rebuilding existing research programs. It is expected that the award helps to further the faculty member's research capability and effectiveness, improves research and teaching at his home institution, and involves undergraduate students in research experiences. The award to Tuskegee University has potential broader impact in a number of areas. The goal of the project is to study fundamental characteristics of jet instability and its potential alteration using an ultra-frequency micro-fluidic actuation technique called resonance enhanced microjets (REM). Instability modification, using REM, has potential applications in augmentation of air-fuel mixing in supersonic flow and control of jet noise. Undergraduate students will gain research experience in experimental fluid mechanics. A course in experimental fluid mechanics that includes topics such as digital data acquisition, random data analysis and gas dynamics will be developed.This project includes the design and fabrication of REM in the ultra-frequency range (above 20 kHz) and the study of their interaction and impact on shear layer dynamics of an air jet in free and cross-flow configuration. The jet properties will be studied using unsteady intrusive probes as well as non-intrusive techniques such as laser based microschlieren and planar scattering imaging. The proposed micro-actuation scheme is expected to modify inherent instabilities of a jet, exciting the most unstable modes and generating high frequency three dimensional vorticities for enhanced entrainment and diffusion. The actuators proposed here can produce high momentum pulsed disturbances up to 50 kHz generating instabilities every 20 microseconds in the cross-flow jet. Since such a time scale is very close to the mixing time of a high-speed combustor, this approach is expected to potentially enhance air-fuel mixing in supersonic flows. Fundamental studies on such a tailored jet flowfield will be useful for designing high-speed combustors with improved air-fuel mixing and flame stability.