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

点击翻译按钮获取中文摘要

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”.