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

这项研究是由NSF工程- UKRI工程和物理科学研究理事会机会NSF 1- 067资助的。任何固体在流体中移动，例如空气或水，都会经历一个阻力阻力，使其运动减慢。汽车、卡车、摩托车、飞机、轮船和潜艇都需要大量的燃料来克服这种阻力，在空气或水中移动。这种阻力的很大一部分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，由于阻力非常小，边界层不会造成真实的危害。然而，在大型物体上，如飞机和卡车，边界层往往是混乱的，因为有很多涡流和漩涡（湍流运动），这给了一个巨大的阻力。边界层从层流到湍流的变化称为层流-湍流转捩。这种变化的知识是运输车辆设计的基本信息，因为它是至关重要的，以预测产生多大的阻力。本项目旨在研究高速飞机上气流的层流-湍流转捩。重点放在飞机凹部的高速边界层上，如机翼底部，因为这些曲面比平面更常见。这些非常快的气流也发生在发动机内部，特别是在涡轮机叶片上，这些叶片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，以全面了解流过凹固体表面的高速边界层何时、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网络物理学发现的兴奋，以及在高速流和先进的网络基础设施方面培养训练有素的劳动力。CBET-EPSRC提案的总体目标是促进对层流所有阶段的基本理解，流过凹固体表面的可压缩边界层中的湍流转变，从自由流扰动夹带到层流边界层开始（即，感受性阶段）通过过渡直到完全湍流。包含感受性阶段是转捩预测的一个基本成分，以前还没有对流向凹曲率的亚音速和超音速附面层流进行过研究。所提出的方法包括先进的非线性渐近理论的基础上的感受性分析，边界层不稳定性计算，和直接数值模拟（DNS）。将进行系统的理论和数值研究，以澄清Gortler涡的作用，这是由凹曲率引起的流向伸长的反向旋转结构，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）和雷诺平均纳维尔-斯托克斯（RANS）相结合，以评估亚网格尺度（SGS）和RANS模型在Gortler涡主导的过渡流中的性能。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.