EAPSI: A Next-Generation of Wind Fence with Multi-Scale Fractal Structure

对于研究流体流动的人来说，了解和控制大气不稳定，如风暴引起的突然空气运动，是非常感兴趣的，因为大气湍流的变化可以用来减少强风。因此，重要的是要了解工程结构，如渗透的防风墙或防风林如何影响各种流入的水流。本研究将探索多尺度分形结构诱导的湍流，以更好地控制气流。这项研究将与浦项科技大学(POSTECH)的李相俊教授合作进行，李相俊教授是定量流动可视化、实验流体力学、钝体空气动力学和生物流体流动方面的专家。由于这项研究涉及的是新一代风障的大气湍流，因此必须拥有合适的实验室设备来模拟真实的条件。主办实验室拥有多个风洞，包括一个大气边界层风洞，以及各种流量测量系统，为开展这项研究提供了一个绝佳的位置。这项研究将有助于设计更有效的防风栅栏，以限制道路和桥梁等关键基础设施上的积雪/沙尘沉积，并减少风对结构本身的整体副作用。以前的研究发现，在平坦的表面上，孔隙率为50%、底部间隙为栅栏高度10%的规则单尺度栅栏被认为是最佳的。由于采用这种孔隙度判据的分形风障在湍流结构上有明显的差异，因此本研究的目的是加深对大气边界层条件下一维和二维多尺度分形栅的诱导流动结构和湍流动能输送的认识。具体地说，利用粒子图像测速技术(PIV)系统地测量了分形栅周围的整个速度场，以揭示在大范围雷诺数范围内分形栅的关键参数对湍流的影响。最终，这项研究将有助于新一代分形风栅栏的设计，它可以从平均风流中提取足够的动能来促进雪/沙沉积，防止颗粒因过大的湍流应力而再动员。该奖项是与韩国国家研究基金会合作资助的。

Understanding and controlling atmospheric instabilities, such as abrupt air movements resulting from a storm, is of great interest to those who study fluid flow as alterations of atmospheric turbulence can be used to reduce strong winds. It is important, therefore, to understand how engineered structures such as porous wind fences or windbreaks affect various incoming flows. This research will explore multi-scale fractal structure-induced turbulence to better control air currents. The research will be conducted in collaboration with Professor Sang Joon Lee of Pohang University of Science and Technology (POSTECH), an expert in quantitative flow visualization, experimental fluid mechanics, bluff body aerodynamics and bio-fluid flows. Because this study is concerned with atmospheric turbulence for new-generation wind fences, it is imperative to have the appropriate laboratory equipment to simulate real-life conditions. The host laboratory has multiple wind tunnels, including an atmospheric boundary-layer wind tunnel, and various flow measurement systems, providing an excellent location to conduct this research. Insights from this research will contribute to engineering more effective wind fences to limit snow/sand deposition on critical infrastructure such as roads and bridges and to reduce the overall side impact of wind on structures themselves.Previous studies found that a regular mono-scale grid fence of 50% porosity and a bottom gap of 10% of the fence height are considered to be optimal over a flat surface. Since significant differences in turbulent structure have been noted using fractal wind fences with this porosity criteria, the goal of this research is to advance knowledge on the induced flow structure and the turbulence kinetic energy transport of 1D and 2D multi-scale fractal fences in atmospheric boundary-layer conditions. Specifically, whole velocity fields will be systematically measured around the fractal fences by Particle Image Velocimetry (PIV) techniques to uncover effects of key parameters of fractal fences on turbulence for a wide range of Reynolds numbers. Ultimately, this research will assist design of new-generation fractal wind fences which can extract sufficient kinetic energy from the mean wind flow to promote snow/sand deposition and prevent particle remobilization from excessive turbulent stresses. This award is funded in collaboration with the National Research Foundation of Korea.