CBET-EPSRC: Transition and Turbulence in Compressible Boundary Layers Subjected to Concave Surface Curvature

这项研究是由NSF工程和物理科学研究理事会机会NSF 1-067资助的。任何在流体中运动的固体，例如空气或水，都会受到阻力，从而减缓其运动。汽车、卡车、摩托车、飞机、轮船和潜艇都需要大量的燃料才能克服这种阻力，在空中或水中移动。这种阻力很大程度上是由表面和流体之间的摩擦效应引起的。这些效应被限制在靠近表面的一个非常薄的区域内，称为边界层。当边界层的运动非常规则和有序(层流运动)时，由于阻力很小，因此不会造成真正的伤害。然而，在飞机和卡车等大型物体上，边界层往往是混乱的，因为有很多漩涡和漩涡(湍流运动)，这会产生巨大的阻力。边界层从层流到湍流的转变称为层流-湍流转变。对这种变化的了解对于运输车辆的设计是必不可少的信息，因为预测产生多少阻力是至关重要的。该项目致力于研究高速飞机上方空气流动中的层流-湍流转变。重点是飞机凹面部分(如机翼底部)上的高速边界层，因为这些曲面比平面要常见得多。这些非常快速的流动也发生在发动机内部，特别是涡轮叶片上，压缩气体使飞机飞行。将与谢菲尔德大学的研究人员合作进行系统的理论和数值研究，以全面了解在凹形固体表面上高速流动的边界层何时、何地以及如何转变为湍流。与研究工作相结合，将开展各种教育活动，向各级学生展示和灌输对网络物理发现的兴奋，并在高速流动和先进的网络基础设施方面培养一支训练有素的劳动力队伍。这项CBET-EPSRC建议的总体目标是通过向完全湍流的转变，促进对可压缩固体表面上流动的可压缩边界层中层流-湍流转变的所有阶段的基本理解，从自由流扰动进入层流边界层(即接受阶段)。感受性阶段的加入是转折预测的一个基本要素，以前从未对具有流向凹曲率的亚音速和超音速边界层流动进行过探索。该方法包括基于先进的非线性渐近理论的感受性分析、边界层不稳定性计算和直接数值模拟。将进行系统的理论和数值研究，以阐明戈特勒旋涡的作用，戈特勒旋涡是由凹曲率引起的流向拉长的反向旋转结构，其动力学极难预测和控制。边界层物理的详细研究还将与大涡模拟(LES)和雷诺平均纳维-斯托克斯(RANS)相结合，以评估戈特勒涡旋主导的过渡流的亚网格尺度(SGS)和RANS模式的性能。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。

This research was funded under the NSF Engineering - UKRI Engineering and Physical Sciences Research Council opportunity NSF 1-067.Any solid body that moves through a fluid, for example air or water, experiences a resistive drag force that slows its motion down. Cars, trucks, motorcycles, airplanes, ships, and submarines all require a lot of fuel to overcome this drag force and move through air or water. A large part of this resistance is caused by friction effects between the surface and the fluid. These effects are confined in a very thin region near the surface, called the boundary layer. The boundary layer causes no real harm when its motion is very regular and ordered (laminar motion) because the resistive force is very small. However, on large bodies, like airplanes and trucks, the boundary layer is often chaotic because there are a lot of vortices and whirls (turbulent motion), which give a huge resistive force. The change of a boundary layer from laminar to turbulent is called laminar-turbulent transition. The knowledge of this change is essential information for the design of transport vehicles because it is critical to predict how much drag force is generated. This project seeks to study laminar-turbulent transition in air flowing over very fast airplanes. The focus is on the high-speed boundary layers over concave parts of the airplanes, like the bottom of the wing, because these curved surfaces are much more common than flat surfaces. These very fast flows also occur inside the engines, over turbine blades in particular, that compress gases to make the airplanes fly. A systematic theoretical and numerical study will be conducted in collaboration with researchers at the University of Sheffield to provide a complete understanding of when, where, and how a high-speed boundary layer flowing over concave solid surfaces transitions to turbulence. Integrated with the research effort, a variety of educational activities will be undertaken to showcase and instill the excitement of cyberphysics discovery in students at all levels, as well as to prepare a highly-trained workforce in high-speed flows and advanced cyberinfrastructure.The overall objectives of this CBET-EPSRC proposal are to advance the fundamental understanding of all the stages of laminar-turbulent transition in compressible boundary layers flowing over concave solid surfaces, starting from the entrainment of the free-stream disturbances into a laminar boundary layer (i.e., the receptivity stage) through transition up to a fully turbulent flow. The inclusion of the receptivity stage is a fundamental ingredient for transition prediction that has not been previously explored for subsonic and supersonic boundary-layer flows subject to streamwise concave curvature. The proposed approach includes receptivity analysis based on advanced nonlinear asymptotic theory, boundary-layer instability computations, and direct numerical simulations (DNS). A systematic theoretical and numerical study will be conducted to clarify the role of Gortler vortices, streamwise-elongated, counter-rotating structures caused by concave curvature, the dynamics of which is extremely difficult to predict and control. The detailed study of boundary-layer physics will also be combined with large-eddy simulations (LES) and Reynolds-averaged Navier-Stokes (RANS) to assess the performance of subgrid-scale (SGS) and RANS models for transitional flows dominated by Gortler vortices.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.