ERI: Wake interactions past two roughness elements in close proximity to a surface

在环境和工程应用中(例如，在工程表面上，两个非常接近的沙丘和两个紧密相继的突起)，在相对光滑的表面上的两个近距离的粗糙元素上的湍流是会遇到的。上游尾迹和下游尾迹之间的相互作用控制着包括阻力和湍流在内的重要流动特征。这个项目的目的是量化和了解在来流中近距离的两个粗糙元素之间的尾迹相互作用。为此，将使用最先进的仪器对各种配置进行流量测量。该项目将在一所本科院校进行，为工程研究提供基础，并加强本科研究培训。该项目将为本科生提供引人入胜的研究经验，他们将在与院系合作的同时获得宝贵的研究培训和指导。高速体积粒子图像测速仪是一种非侵入式激光诊断流动测量技术，将用于测量位于近距离且浸没在湍流边界层中的两个圆柱形粗糙元素上的流动。钢瓶将被放置在不同的配置中，以改变上游钢瓶保护下游钢瓶免受到来的高动量气流的影响的程度。这些实验将允许描述丰富的流动物理：湍流边界层下部的两个3D剪切层的相互作用。其目的是1)量化两个圆柱粗糙度元素尾迹之间的流动相互作用；2)表征孤立的圆柱粗糙度元素脱落的涡旋结构，并确定由于上游圆柱的引入而对这些结构的修改；3)研究附加上游元素(即由2、3和4个上游元素遮挡)对捕获的流动物理的影响；4)量化粗糙度对边界层及其相干结构的扰动；以及5)提取时空分辨的流动描述，说明遮蔽流的物理分布。在空间和时间上分辨的测量将有助于填补文献中关于两个近距离粗糙元素上的流动的空白，提供对所涉及的丰富流动物理的洞察，并提供基准结果来帮助其他研究人员进行建模和验证工作。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。

The turbulent flow over two roughness elements in close proximity on an otherwise relatively smooth surface is encountered in environmental and engineering applications (e.g., two dunes in close proximity and two protrusions in close succession on an engineered surface). The interactions between the upstream wake and the downstream wake govern important flow features including drag and turbulence. This project aims to quantify and understand the wake interactions between two roughness elements in close proximity under incoming turbulent flow. For this purpose, flow measurements will be made for a wide range of configurations using state-of-the-art instrumentation. The project will be performed at an undergraduate institution providing foundation for engineering research and enhancing undergraduate research training. The project will provide engaging research experiences for undergraduate students who will gain valuable research training and mentoring while working alongside faculty.High-speed volumetric particle image velocimetry, a non-intrusive laser-diagnostic flow measurement technique, will be used to measure the flow over two cylindrical roughness elements positioned in close proximity and immersed in a turbulent boundary layer. The cylinders will be positioned at various configurations to vary the degree by which the upstream cylinder shelters the downstream cylinder from the incoming high-momentum flow. The experiments will allow for the characterization of rich flow physics: the interaction of two 3D shear layers in the lower portion of a turbulent boundary layer. The objectives are to 1) quantify the flow interactions between the wakes of the two cylindrical roughness elements; 2) characterize the vortical structures shed from isolated cylindrical roughness elements and identify the modifications to these structures due to the introduction of an upstream cylinder; 3) investigate the effects of additional upstream elements (i.e., sheltering by 2, 3, and 4 upstream elements) on the captured flow physics, 4) quantify the roughness-induced perturbation to the boundary layer and its coherent structures; and 5) distill a spatiotemporally-resolved flow description that illustrates sheltering flow physics across a wide range of arrangements. The spatially- and temporally-resolved measurements will aid in addressing a gap in the literature on the flow over two roughness elements in close proximity, offer insight into the rich flow physics involved, and provide benchmark results to aid other researchers in their modeling and validation efforts.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.