Collaborative Research: Effect of Helicity on the Development of Free-Shear Turbulence at High Reynolds Number

螺旋度是一种固有的流体流动特性，其物理上与具有螺旋形结构的流体的局部流线相关。在风能利用中，涡轮机的湍流尾迹会产生非零螺旋度。该尾流的速度对由风力发电场中的下游涡轮机产生的功率具有强烈的影响。本计画将探讨操控垂直轴风力涡轮机（VAWT）所产生的尾流螺旋度对尾流紊流发展的影响。特别是，螺旋度和湍流夹带的动能，这是关键的尾流速度恢复之间的关系，将是一个主要的焦点。该项目是一项合作努力，利用现场，实验室和计算设施，使用最先进的设备和新颖的方法，以克服调查高度湍流的挑战。该项目还将包括教育活动，例如让本科生研究人员参与，并强调流体基础物理学与风能应用之间的联系，这一为期三年的项目的总体目标是了解螺旋度对高雷诺数流动中自由剪切湍流发展的影响。采用VAWT作为“螺旋度发生器”，其中涡轮机尾流中的初始螺旋度由涡轮机叶片几何形状和转速控制，并检查湍流尾流的后续演变。这项合作研究工作的关键组成部分将包括：（1）使用3D粒子跟踪速度测量来量化大气边界层流中的公用事业规模VAWT的尾流螺旋度的现场实验，（2）使用时间分辨立体粒子图像速度测量来获得VAWT尾流的高时空数据的风洞实验，（3）大涡模拟，通过实验中不易测量的手段有效地探测螺旋度的影响。这一共同努力为研究高雷诺数下螺旋度的物理效应提供了一个机会，这有助于获得基本的流体动力学知识，这些知识可用于为湍流模型提供信息，或更直接地用于风力发电等应用。该奖项反映了NSF的法定使命，并被认为值得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来支持。

Helicity is an inherent fluid flow property that physically relates to the local streamlines of a flow having helical-shaped structure. In the application of wind energy, a wind turbine can induce non-zero helicity in its turbulent wake. The speed of this wake flow has a strong impact on the power produced by a downstream turbine in a wind farm. This project will examine the effect of manipulating wake helicity generated by a vertical-axis wind turbine (VAWT) on the development of wake turbulence. In particular, the relationship between helicity and the turbulent entrainment of kinetic energy, which is critical to wake flow speed recovery, will be a primary focus. The project is a collaborative effort that exploits field, laboratory, and computational facilities using state-of-the-art equipment and novel methodologies to overcome the challenges of investigating highly turbulent flows. The project will also encompass education activities, such as involving undergraduate student researchers, facilitated by an emphasis on the connection between the fundamental physics of fluids and wind energy applications.The overall goal of this three-year project is to develop an understanding of the effect of helicity on the development of free-shear turbulence in high Reynolds number flows. A VAWT is employed as a 'helicity generator', where initial helicity in the turbine wake is controlled by turbine blade geometry and rotational speed, and the subsequent evolution of the turbulent wake is examined. Key components of this collaborative research effort will include: (1) field experiments to quantify wake helicity for utility-scale VAWTs in an atmospheric boundary layer flow using 3D particle tracking velocimetry, (2) wind tunnel experiments to achieve high spatio-temporal data of the VAWT wake using time-resolved stereoscopic particle image velocimetry, and (3) large eddy simulations to efficiently probe the effects of helicity by means not easily measured in the experiments. This combined effort offers an opportunity to investigate the physical effects of helicity at high Reynolds number, which contributes to basic fluid dynamics knowledge that could be used to inform turbulence models or more directly in applications such as wind farming.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.