Flow Control for Unsteady Aerodynamics of Pitching/Plunging Airfoils

本项目研究了一些非定常空气动力学的通用流动控制方案。在这一建议的背景下，非定常空气动力学是指边界条件表现出时间依赖性的流动情况。这种流动在大量的实际应用中是非常常见的，例如旋翼机叶片、风力涡轮机叶片、扑翼飞行器或受到湍流和/或阵风影响的飞机或地面车辆。拟议的项目考虑了这种流动，但特别研究了引入流动控制措施的可能性，以减轻不稳定的不良影响，或提高组件的整体性能或使用寿命。非定常气动与流动控制的结合是一个较新的研究领域，因此选择通用构型来探讨其物理特性和可实现的控制权限。特别是俯仰和俯冲翼型的前缘和后缘涡形成被认为是具有代表性的，适合于这种开创性的研究。这些涡的空气动力学后果，其发展对翼型和分离后，一些有限的增长时间，可以是有利的或有害的，取决于应用。有害影响包括整体气动性能恶化（深度失速、升力滞后）、疲劳加速、振动和噪音增加。另一方面，旋涡在翼型也可以提高升力，如用于昆虫飞行，并在某种程度上，直升机。本研究将采用介质阻挡放电（DBD）等离子体作动器和合成射流作动器进行流动控制。两者都是快速作用的，适合集成到开环或闭环控制策略中；因此，能够减轻由于意外和/或未知的流动扰动而产生的不良影响。本课题的科学目标包括：通过参考实验和数值仿真，提出执行机构最合适的位置和运行方式，并通过实验和仿真验证控制策略。该项目的结果将是增加对执行器控制权限的理解，以及在实际应用中实现的具体建议。

This project examines some generic flow control schemes for unsteady aerodynamics. In the context of this proposal unsteady aerodynamics are flow situations in which the boundary conditions exhibit time dependence. Such flows are a very common occurrence in a large number of practical applications, such as rotorcraft blades, wind turbine blades, flapping flyers or in aircraft or ground vehicles subject to turbulence and/or gusts. The proposed project considers such flows, but examines especially the possibility of introducing flow control measures, either to mitigate unwanted effects of the unsteadiness or to improve overall performance or lifetime of components. The combination of unsteady aerodynamics and flow control is a rather new research field and therefore generic configurations are chosen to explore the physics involved and the achievable control authority. In particular the leading and trailing edge vortex formation found in pitching and plunging airfoils are considered representative and suitable for such pioneering studies. The aerodynamic consequence of these vortices, which develop on the airfoil and separate after some finite growth time, can be either beneficial or detrimental, depending on application. Detrimental effects include deteriorated overall aerodynamic performance (deep stall, lift hysteresis), accelerated fatigue, or increased vibration and noise. On the other hand, vortices on an airfoil can also enhance lift, as used in insect flight and, to some extent, on helicopters. The actuators to be used in this study for flow control are the dielectric barrier discharge (DBD) plasma actuator and the synthetic jet actuator. Both are fast acting and are suitable to be integrated into either open-loop or closed-loop control strategies; hence capable of mitigating unwanted effects due to unexpected and/or unknown on-flow perturbations. The scientific goals of the project include postulating, through reference experiments and numerical simulations, the most appropriate placement and operation of the actuators, and verification of the control strategy through experiment and simulation. The outcome of the project would be an increased understanding of the control authority of the actuators and specific recommendations for implementation in real-world applications.