Computational and experimental demonstrations of the hybrid control concept of vibration and noise on helicopters

降低直升机的振动和噪声是当今航空航天领域的研究重点。振动不仅会恶化乘坐品质，还会增加部件疲劳和维护成本，是导致飞行员慢性背痛和提前退休的主要原因，并限制直升机的前进速度。另一方面，噪音会对乘客的舒适度和直升机的环境足迹产生负面影响。就像在其他工程领域一样，振动和噪声是强耦合现象，因为声波是通过振动一个组件(像扬声器一样)产生的：噪声源。在直升机上，有许多振动和噪声源，如发动机、变速箱或尾旋翼。然而，大部分振动和噪声是由主旋翼本身通过空气动力学(如激波、动态失速、叶片涡干扰等)产生的。以及叶片中发生的动力学现象(如叶片拍打和超前滞后运动)。这些问题的发生是由于直升机飞行的本质，并与旋翼空气动力学有内在联系。尽管大部分噪声和振动来自主旋翼，但现在的生产直升机只采用基于机身的振动和噪声控制技术，这些技术通常相对较重。因此，人们对开发更轻的基于转子的系统非常感兴趣，这种系统可以从根本上解决振动和噪声-通过单独控制每个叶片来解决转子叶片本身的振动和噪声。已经有各种尝试来开发基于转子的主动控制系统。它们几乎都是“流量控制”概念，即它们试图改变作用在叶片上的气动力，如主动控制襟翼、主动扭曲的转子叶片、主动控制的后缘装置等。这些装置的问题是需要相对较大的驱动功率，因为它们对抗产生振动的力。另一方面，卡尔顿大学在过去的10年里一直在追求一种独特的、独创的想法，即所谓的叶片“刚度控制”概念，即控制叶片的结构响应，而不是作用在叶片上的气动力。刚度控制基于动态系统的参数激励理论，有望比流量控制系统使用更少的驱动功率。另一个需要注意的要点是，同时降低直升机旋翼上的振动和噪声是非常具有挑战性的。提案中概述的研究目标是通过计算和实验证明，通过卡尔顿大学由Feszty教授和Nitzsche教授构思的独特的“混合控制”概念，可以同时减少振动和噪声。这是基于使用两个独立的控制系统：“刚度控制”和“流量控制”。

Reduction of vibration and noise on helicopters is a research priority nowadays in the aerospace sector. Vibration not only deteriorates ride quality, but also increases component fatigue and maintenance costs, it is the main source for chronic back pain and early retirement of pilots and it limits the forward flight speed of helicopters. Noise, on the other hand, negatively affects passenger comfort and the environmental footprint of helicopters. Just as in other engineering fields, vibration and noise are strongly coupled phenomena, since sound waves are generated by vibrating a component (acting like a speaker): the noise source. On helicopters, there are numerous sources of vibration and noise, such as the engine, the gearbox or the tail rotor. However, most of vibration and noise is generated by the main rotor itself through the aerodynamics (such as the appearance of shock waves, dynamic stall, Blade Vortex Interaction, etc.) and dynamics phenomena occurring in blades (such as blade flapping and lead-lag motions). These occur due to the very nature of helicopter flight and are inherently associated with rotor aerodynamics. Although most of noise and vibration originates on the main rotor, production helicopters nowadays feature only fuselage based vibration and noise control technologies, which are usually relatively heavy. Therefore, there is great interest in developing lighter, rotor-based systems, which could tackle vibration and noise at their very source – on the rotor blade itself by individually controlling each blade. There have already been various attempts to develop rotor-based active control systems. Nearly all of them are “flow control” concepts, i.e. they try to alter the aerodynamic forces acting on the blades, such as an actively controlled flap, actively twisted rotor blades, actively controlled trailing edge devices, etc. The problem with these is the need for relatively large actuation power, since they act against the forces creating vibration. Carleton University – on the other hand – has been pursuing a unique and original idea in the past 10 years, the so called “stiffness control” concept of blades, in which the structural response of the blades is to be controlled instead of the aerodynamic forces acting on the blades. Stiffness control is based on the theory of parametric excitation of dynamic systems and promises to use much less power for actuation than flow control system. Another important point to note is that it is very challenging to simultaneously reduce vibration and noise on helicopter rotors. The goal of the research outlined in the proposal is to demonstrate computationally and experimentally that simultaneous reduction of vibration and noise is possible by the unique “hybrid control” concept conceived at Carleton University by Prof. Feszty and Nitzsche. This is based on using two independent control systems: a “stiffness control” and a “flow control”.