Reduced In-Plane, Low-Frequency Noise of an Active Flap Rotor

Sim, Ben Wel-C.; Janakiram, Ram D.; Lau, Benton H.

doi:10.4050/jahs.59.022002

Cited by 22 publications

(11 citation statements)

References 4 publications

(6 reference statements)

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“…However, the results from the tests were analyzed carefully later (Ref. 132) and it was noted that the noise reduction levels were accompanied by large increases, of up to 300%, in the longitudinal and lateral vibratory 5/rev hub loads, which implies limitations on the noise reduction strategy pursued in the test. Therefore, in the conclusions of Ref.…”

Section: The Smart Rotor Testmentioning

confidence: 99%

On-Blade Control of Rotor Vibration, Noise, and Performance: Just Around the Corner? The 33rd Alexander Nikolsky Honorary Lecture

Friedmann¹

2014

j am helicopter soc

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A concise review of the active control approaches for vibration reduction in rotorcraft is presented. Next, the evolution and status of higher harmonic control and pitch link actuated individual blade control is presented since these serve as the foundations of on blade control. Despite the success of these approaches, demonstrated by both full-scale wind tunnel and flight tests, higher harmonic control and pitch link actuated individual blade control have not managed to earn their way onto a production helicopter. An alternative, on blade control, is defined as a special implementation of individual blade control, where the control surfaces are located on the rotating blade and each blade has its own controller. A concise description of four on blade devices: (1) the actively controlled flap, (2) the active twist rotor, (3) the active tip rotor, and the (4) deployable Gurney flap, or microflap, is presented. An outline of an aeroelastic response modeling capability used to simulate active vibration and noise reduction using flaps or microflaps is presented. The simulation is a thread that links the various parts of the paper. Next, selected results from simulations and scale wind tunnel model tests on active flaps are used to provide insight on the operational and modeling aspects of these systems. Full-scale wind tunnel and flight tests are presented as culmination of the research effort invested in active flap rotors. Then, the evolution and application of the active twist rotor, and deployable Gurney flaps, or microflaps, is presented. The paper concludes with lessons learned and speculation about the potential implementation of on blade control on production rotorcraft.

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Section: The Smart Rotor Testmentioning

confidence: 99%

On-Blade Control of Rotor Vibration, Noise, and Performance: Just Around the Corner? The 33rd Alexander Nikolsky Honorary Lecture

Friedmann¹

2014

j am helicopter soc

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“…The far-field acoustic environment in front of the helicopter is characterized by low-frequency sound pressure level (LFSPL), consisting of the first through sixth blade-passage frequency (BPF) harmonic components of the rotor noise, which are the principal components of in-plane low-frequency noise [14]. The LFSPL is computed on a spherical segment located at a distance of 10R in front of the rotor hub, with an azimuth angle between 135 and 225 deg and an elevation angle between −90 and 15 deg, as shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Several active control means such as higher harmonic control (HHC), pitch link actuated individual blade control, and on-blade control (OBC) implemented through a trailing-edge flap or a microflap have been studied for noise control [13]. These techniques modify the blade airloads to influence the BVI interactions for BVI noise reduction [3] or to generate an "antinoise" signal for in-plane noise reduction [14]. However, implementation of active control on a production helicopter has an associated cost that needs to be justified by sufficient benefits.…”

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confidence: 99%

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Active and Passive Helicopter Noise Reduction Using the AVINOR/HELINOIR Code Suite

Chia

Duraisamy

Padthe

et al. 2018

Journal of Aircraft

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A suite of computational tools capable of predicting in-plane low-frequency rotorcraft noise and its control using blade-tip geometry modifications is developed. The combined code, consisting of AVINOR, a comprehensive rotorcraft analysis code, and an acoustic code called HELINOIR, is first validated against wind-tunnel tests and subsequently verified by comparing with computational results. Three rotor configurations resembling the Messerschmitt-Bölkow-Blohm BO105 with a tip sweep, dihedral, and anhedral were simulated for level flight at a moderate advance ratio. The impact of passive blade geometry modification on in-plane noise and vibration is studied and compared to the in-plane noise reduction obtained using a single 20% chord active plain trailing-edge flap with a feedback microphone on the left boom. Active control, which is implemented using an adaptive higher harmonic control algorithm, reduces in-plane low-frequency sound pressure levels below the horizon by up to 6 dB, but there is an increase in vibratory loads. The tip dihedral reduces low-frequency sound pressure level by up to 2 dB without a vibratory load penalty, but there is an increase in the midfrequency sound pressure levels. The tip sweep and tip anhedral increase in-plane low-frequency sound pressure level below the horizon. There is a general tradeoff associated with in-plane low-frequency sound pressure level reduction, vibration performance, and midfrequency sound pressure level.

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“…As the swashplate is eliminated, the control system of the ECR can be simplified, which can effectively reduce the empty weight and the parasite drag of the helicopter [2]. In addition to primary control, applying harmonic or nonharmonic motions, the trailing-edge flap system could also be used for rotor vibration reduction [3,4], noise alleviation [5][6][7], and performance enhancement [8,9]. e helicopter is the quietest vertical take-off and landing (VTOL) aircraft, but its noise level can still be high enough to compromise its utility unless specific attention is given to designing for low noise [10].…”

Section: Introductionmentioning

confidence: 99%

Electrically Controlled Rotor Blade Vortex Interaction Airloads and Noise Analysis Using Viscous Vortex Particle Method

et al. 2019

Shock and Vibration

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An electrically controlled rotor (ECR), also called a swashplateless rotor, replaces a swashplate with a trailing-edge flap system to implement primary rotor control. To investigate the aerodynamic characteristics of an ECR in blade-vortex interaction (BVI) condition, an analysis model based on the viscous vortex particle method, ECR blade pitch equation, and the Weissinger-L lifting surface model is established. In this model, the ECR wake flow field vorticity is discretized as multiple vortex particles, and the vorticity-velocity form of the Navier-Stokes equation is solved to simulate the transport diffusion of the vorticity. The flap motion-inducing blade-pitch movement is obtained by solving the ECR blade-pitch movement equation via the Runge–Kutta fourth-order method. On the basis, BVI noise radiation of an ECR is evaluated using the Ffowcs Williams and Hawkings (FW-H) equation. Based on the present prediction model, the aerodynamic and acoustic characteristics of a sample ECR in BVI condition are analyzed. The results show that since the BVI event of the ECR on the advancing side is mainly caused by the interaction between the flap tip vortex and the blade, the blade spanwise range of ECR BVI occurrence on the advancing side is smaller than that of the conventional rotor. In addition, the magnitude of the maximum sound pressure level on the advancing side as well as on the retreating side of the ECR is also different from that of the conventional rotor, which is consistent with the difference in the airloads between the ECR and conventional rotor. Furthermore, a study was performed to examine the effect of the pre-index angle on the BVI-induced airloads and noise. The amplitude of the impulsive airloads of the ECR on the advancing side is increased with the increase in pre-index angle, while the amplitude of the impulsive airloads of the ECR on the retreating side is decreased. Indeed, when the pre-index angle of the sample ECR is 8 degrees, the retreating-side noise radiation lobe is almost disappeared. In addition, the different intensity of wake vorticity is the main reason for the differences of the BVI-induced airloads and noise among the ECR with different pre-index angles.

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Reduced In-Plane, Low-Frequency Noise of an Active Flap Rotor

Cited by 22 publications

References 4 publications

On-Blade Control of Rotor Vibration, Noise, and Performance: Just Around the Corner? The 33rd Alexander Nikolsky Honorary Lecture

On-Blade Control of Rotor Vibration, Noise, and Performance: Just Around the Corner? The 33rd Alexander Nikolsky Honorary Lecture

Active and Passive Helicopter Noise Reduction Using the AVINOR/HELINOIR Code Suite

Electrically Controlled Rotor Blade Vortex Interaction Airloads and Noise Analysis Using Viscous Vortex Particle Method

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