Blade-vortex interaction noise reduction with active twist smart rotor technology

Abstract

The results of this analytical feasibility study suggest that active blade twist technology is a viable means to reduce blade-vortex interaction (BVI) noise in rotorcraft systems. A linearized unsteady aerodynamics analysis was formulated and successfully validated with computation fluid dynamics (CFD) analysis. A simple control scheme with three control points was found to be effective for active BVI noise reduction. Based on current-day actuation technology where one to two degrees of twist per blade activation span is expected, measurable noise reductions of 2-4 dB were predicted for the relatively strong, close vortex interactions. For weaker vortex interactions, reductions of 7-10 dB were predicted. The required twist actuation per blade span for complete unsteady loading cancellation, however, may be infeasible because of the large stroke and high-frequency activation requirements.

Closed-loop controlled vortex-airfoil interactions

“…IBC allowed the independent control of each blade of a helicopter with servohydraulic actuators, resulting in a reduction in the BVI noise by 12 dB. Chen et al 12 used surface-bounded piezoceramic actuators or fiber composites to twist an airfoil, achieving a 10 dB reduction in the BVI noise. Straub et al 13 applied piezoelectrically driven trailing edge flaps to all blades of a MD900 light utility helicopter.…”

Investigation on a High-Frequency Controller for Rotor BVI Noise Alleviation

“…Besides problems related to the increase of weight and complexity of the actuation devices, the way these controllers act for BVI noise reduction often corresponds to an increase in low-frequency noise content and in rotor vibration levels. 2,6 Furthermore, the actuators that are typically used for the conventional active control are characterized by limited frequency bandwidth and high vulnerability of the hydraulic systems. Active materials help to overcome most of these limitations, since they operate through the direct conversion from the electrical signal to the mechanical deformation of the material.…”

“…Note that the technological feasibility of the proposed highfrequency controller is still an open issue, although much research is under development in this field. 6 Thus, the goal of this paper is to explore its potential performance, as well as to provide an efficient procedure for synthesis and application of control law.…”

Development of a Span-Extending Blade Tip System for a Reconfigurable Helicopter Rotor

“…Another approach is to vary the aerodynamic forces on the blades by dynamically changing the geometry of the airfoil sections. Recent advances in adaptive materials have led to a variety of schemes for on-blade actuation, such as adaptive twist of the rotor blade, 4,5,6 trailing edge flaps, 1,7,8,9 and active camber control. 10,11 Of these concepts, active twist of the rotor blade involves a large weight penalty due to the distributed nature of the actuators.…”