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

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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.