Exploration and Control of Transverse Jet Shear Layer Instabilities

建议编号：CTS-0457413研究人员：A.Karagozianinn研究：加州大学洛杉矶分校横向喷流剪切层不稳定性的探索和控制这项研究的学术价值包括考察近场剪切层不稳定性的基本演变和发展横流或横向喷流中喷流的这种不稳定性控制方法。这种流动与许多实际应用有关，例如叶轮机械和喷气发动机燃烧室的冷却，在这些应用中，有效的控制可以显著提高效率和减少污染物排放。随着横流速度的增加和射流从“自由射流”向“横向射流”的转变，在先前的NSF资助下，不稳定性的频谱特征发生了显著的变化。稳定性特性的这种变化表明，在吹风比达到临界值时，横向射流存在从对流不稳定到绝对不稳定或自激的转变。这种稳定性特征可以解释横向射流与周围气体混合的能力，其混合方式优于自由射流。横流中射流稳定性特性的这些差异为未来优化横向射流穿透、混合和扩散的控制研究提供了一种战略方法。该程序将通过实验、理论和数值模拟，在大范围的射流和横流条件下，更全面地描述这些不稳定性的性质。在这种控制方法中，还将探索和利用螺旋模式在射流稳定性中的作用。反馈和前馈控制将在对喷气控制方法至关重要的时间波形整形中发挥重要作用，并将涉及广泛的测试和分析。拟议的项目产生了重大的更广泛的影响，包括本科生研究人员的参与。将继续为当地高中生和将来的中学生提供外展介绍和示范，特别侧重于女童子军和公立学校的学生。将为当地高中生提供在暑期获得实验室经验的机会。加利福尼亚州削减了对公立学校MESA(数学工程科学成就)项目的资助，这使得加州大学洛杉矶分校(UCLA)等大学将扩展项目扩展到公立中学和高中变得更加重要，以此作为鼓励未来工程师和科学家发展的一种手段。拟议的项目将为开展这一外联活动提供适当的机制。

PROPOSAL NO.: CTS-0457413PRINCIPAL INVESTIGATOR: A. KARAGOZIANINSTITUTION: UNIVERSITY OF CALIFORNIA-LOS ANGELES EXPLORATION AND CONTROL OF TRANSVERSE JET SHEAR LAYER INSTABILITIES The intellectual merits of this study involve an examination of the fundamental evolution of near field shear layer instabilities and the development of approaches in the control of such instabilities for the jet in crossflow, or transverse jet. This flow is related to many practical applications such as cooling in turbomachinery and jet engine combustors within which effective control could lead to significant improvements in efficiency and reductions in pollutant emissions. As the crossflow velocity increases and the jet transitions from the "free jet" to the "transverse jet", remarkable alterations in the spectral character of the instability have been observed under a prior NSF grant. The nature of this change in the stability characteristics suggests that at critical values of blowing ratio, there is a transition in the transverse jet from being convectively unstable to absolutely unstable or self-excited. Such stability characteristics may explain the transverse jet's ability to mix with surrounding gases in a superior manner to that of the free jet. These differences in the stability characteristics of the jet in crossflow suggest a strategic approach for future control studies in optimizing transverse jet penetration, mixing, and spread. This program will characterize the nature of these instabilities more completely, for a wide range of jet and crossflow conditions, through experiments, theory, and numerical simulations. The role of helical modes in the jet stability will also be explored and exploited in this control methodology. Feedback and feed-forward control will feature prominently in the temporal waveform shaping that is critical to this jet control approach, and will involve extensive testing and analysis. The proposed program has significant broader impacts, including involvement of undergraduate researchers. Outreach presentations and demonstrations will continue to be provided for local high school and, in the future, middle school students, with special focus on Girl Scout troops and students at public schools. Opportunities for local high school students to gain laboratory experiences in the summer will be provided. Cutbacks in funding by the state of California to the public schools' MESA (Mathematics Engineering Science Achievement) programs has made it even more important for universities such as UCLA to extend outreach programs to public middle schools and high schools as a means of encouraging the development of future engineers and scientists. The proposed project will afford an appropriate mechanism for this outreach to take place.