Discovering the Transition Mechanisms in Fundamental Canonical Flows and in Idealized Propulsion Component Systems

流动从确定性层流状态到随机湍流状态的转变过程在理论上具有挑战性，在技术上也具有重要意义，指出在转变之前、过程中和转变后，表面摩擦、表面换热和声发射的水平都有明显的不同。我们的研究计划集中在一个统一的主题上，即在基本正则流和应用航空工程系统中发现层流到湍流的转变机制。典型的过渡流包括Blasius边界层的自然和旁路过渡(大部分已被了解)，以及百年未解决的Osborne Reynolds管过渡，而航空应用过渡流可以在叶轮机械的定子-转子级中找到，这构成了喷气发动机推进系统的基石。我们致力于建立一个高度创新和有影响力的研究计划，专注于两个方面：确定国际流体研究界普遍和深刻感兴趣的重大前沿、悬而未决的问题；开发和使用高精度、充分验证的最先进的研究方法，即超大规模、物理逼真、空间发展的直接数值模拟(DNS)。 我们的最新成果已发表在《流体力学年度评论》、《美国国家科学院院刊》和《流体力学杂志》上。我们的域名系统数据已被全球范围内的管流和边界层研究人员用作基准。 在这里，我们建议提升我们的研究计划，通过对Osborne Reynolds管流转变、von Karman转盘边界层转变以及理想涡轮叶片-转子级跨中段多模式转变流的精确动力学进行基本机理研究，来解决对流体力学领域重要的新挑战。 我们的愿景是解决尚未解决的重大基础和工程过渡流动问题，以便我们的发现可以纳入未来的本科生和研究生教科书。奥斯本-雷诺管过渡、von Karman转盘过渡和理想定子-转子阶段多模式过渡的目标问题构成了一个连贯的研究主题，重点关注对过渡建模具有潜在工程意义的机理。我们的方法是创新的，因为我们从层流开始，经过过渡，一直到完全发展的湍流，进行空间发展的超大规模数值模拟。拟议的发现计划推动了最先进的边界，推动了过渡研究领域的发展，并使我们能够与世界上一些最好的团队进行国际竞争。

The processes of flow transitioning from a deterministic laminar state to a stochastic turbulent one are both intellectually challenging and technologically important, noting that the levels of skin-friction, surface heat transfer and sound emission are all markedly different before, during and after the transition. Our research program centers on the unifying theme of discovering laminar-to-turbulent transition mechanisms in fundamental canonical flows as well as in applied aeronautical engineering systems. Canonical transitional flows include the Blasius boundary layer's natural and bypass transition (mostly understood), and the century-old unresolved Osborne Reynolds pipe transition, whereas applied aeronautical transitional flows can be found in a turbomachinery stator-rotor stage, which forms the building block of jet engine propulsion system. We aspire to building a highly innovative and impactful research program by focusing on two aspects: identify major cutting-edge, unresolved problems that are of general and profound interest to the international fluids research community; develop and use highly accurate, thoroughly validated, state-of-the-art investigative approach, namely, very-large-scale, physically-realistic, spatially-developing direct numerical simulation (DNS). Our recent results have been published at the Annual Review of Fluid Mechanics, Proceedings of the National Academy of Science of the United States of America, and the Journal of Fluid Mechanics. Our DNS data have been used worldwide as benchmarks by pipe flow and boundary layer researchers. Here, we propose to elevate our research program to address new challenges that are important to the field of fluid mechanics by performing fundamental mechanism investigations on the precise dynamics of transition in the Osborne Reynolds pipe flow transition, the von Karman rotating disk boundary layer transition, and the multi-mode transitional flow in the mid-span section of one idealized turbine vane-rotor stage. Our vision is to tackle major unresolved fundamental and engineering transitional flow problems so that our discoveries could be incorporated into future undergraduate and graduate textbooks. The identified target problems of Osborne Reynolds pipe transition, von Karman rotating disk transition, and multi-mode transition in idealized stator-rotor stage constitute a coherent research theme focusing on the mechanisms with potential engineering relevance for transition modeling. Our approach is innovative in that we perform spatially-developing, very-large-scale DNS start from laminar, through transition, all the way to fully-developed turbulence. The proposed discovery program pushes the boundary of the state-of-the-art, moves the transition research field forward, and enables us to compete internationally with some of the best groups in the world.