The Influence of Turbulence on the Flow Structures and Loads on Airfoils and Wings at Low Reynolds Numbers

低雷诺数下湍流对流动结构及翼型和机翼载荷的影响

• 批准号: 262029165
• 负责人: Dr.-Ing. Rainer Hain
• 金额: --
• 依托单位: Institut für Strömungsmechanik und Aerodynamik (LRT-7)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2017-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/262029165?language=en
• 关键词: Influence; Turbulence; Flow; Structures; Loads

Micro Air Vehicles (MAVs) are typically small (< 0.5 m) and remote controlled or autonomous aircrafts that fly at low speeds (< 10 m/s) and are envisaged to carry out a number of vital missions including surveillance, assist in search and rescue, act as communication relay, etc. During these missions, MAVs will spend extended durations within the lowest region of the atmosphere, known as the Atmospheric Boundary Layer (ABL), and they will be expected to maintain stable flight. Though the advantages and uses of MAVs are well established, their design, development and deployment has been hindered mainly due to the lack of understanding of the flow dynamics associated with their flight domain.The flow field within the ABL can be extremely complex and unsteady. The interaction between the airflow and structures and obstacles present on the Earth's surface and other thermal effects rendered the flow to become very turbulent. The free-stream turbulence present within the ABL can be characterized using the turbulence intensity and integral length scale. Turbulence intensities up to 30% and integral length scales ranging less than a meter to many tens of meters have been observed in flow measurements taken within the ABL. MAVs in flight would be exposed to both low Reynolds number effects (by virtue of their size and flight speed) and high levels of free-stream turbulence (commonly present within the ABL). Therefore, to make MAVs flyable in variable weather conditions, there is a real necessity to understand the influence of large scale free-stream turbulence on airfoils and wings at relevant Reynolds numbers.State-of-the-art measurement techniques will be applied to highlight the instantaneous as well as statistical interactions between free-stream turbulence and the flow over airfoils/wings under various turbulence conditions. Under each turbulence condition, for an airfoil simultaneous measurements of surface pressure and velocity profiles using PIV will be made to highlight the influence of turbulence on the sectional loads and moments. Subsequently, force and velocity measurements will be taken over a low aspect ratio wing to assess wing performance and shed further light on the influence of turbulence on the integrated forces and moments. Detailed comparisons between the pressure/force and PIV measurements will be used to relate instantaneous disturbances to the resulting flow structure and loads experienced by the airfoil/wing.The results obtained from the investigations to be performed will give a detailed insight into the flow physics over airfoils and wings under different turbulent conditions as they occur in reality when MAVs operate in ABL. The understanding of these processes is of fundamental interest for development of MAV control systems as well as active flow control devices which may be applied in the future to increase the performance of MAVs under such conditions.

微型飞行器 (MAV) 通常是小型 (< 0.5 m) 的遥控或自主飞机，以低速 (< 10 m/s) 飞行，旨在执行许多重要任务，包括监视、协助搜索和救援、充当通信中继等。在这些任务期间，MAV 将在大气层最低区域（称为大气边界层 (ABL)）内长时间停留，并且它们将 预计航班将保持稳定。尽管微型飞行器的优点和用途已广为人知，但其设计、开发和部署受到阻碍，主要是由于缺乏对其飞行域相关的流动力学的了解。空中边界线内的流场可能极其复杂且不稳定。气流与地球表面存在的结构和障碍物之间的相互作用以及其他热效应使气流变得非常湍流。 ABL 中存在的自由流湍流可以使用湍流强度和积分长度尺度来表征。在 ABL 内进行的流量测量中观察到湍流强度高达 30%，整体长度范围从一米到几十米。飞行中的微型飞行器将受到低雷诺数效应（由于其尺寸和飞行速度）和高水平的自由流湍流（通常存在于 ABL 内）的影响。因此，为了使微型飞行器能够在多变的天气条件下飞行，确实有必要了解大规模自由流湍流在相关雷诺数下对机翼和机翼的影响。将应用最先进的测量技术来突出各种湍流条件下自由流湍流与机翼/机翼上的流动之间的瞬时和统计相互作用。在每种湍流条件下，将使用 PIV 对翼型的表面压力和速度剖面进行同步测量，以突出湍流对截面载荷和力矩的影响。随后，将对低展弦比机翼进行力和速度测量，以评估机翼性能，并进一步阐明湍流对综合力和力矩的影响。压力/力和 PIV 测量之间的详细比较将用于将瞬时扰动与由此产生的流动结构和机翼/机翼所经历的载荷联系起来。从要执行的研究中获得的结果将详细了解 MAV 在 ABL 中运行时实际发生的不同湍流条件下机翼和机翼上的流动物理现象。了解这些过程对于开发 MAV 控制系统以及主动流量控制装置至关重要，这些系统和主动流量控制装置可能在未来用于提高 MAV 在此类条件下的性能。