Radiation and directionality characteristics of advancing side blade-vortex interaction (BVI) noise

Schmitz, Fredric H.; Sim, Ben Wel-C.

doi:10.2514/6.2000-1922

Cited by 13 publications

(8 citation statements)

References 7 publications

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“…There it was shown that a simple model of the blade vortex interaction process could provide a wide variety of new insights into the helicopter BVI noise radiation. More recently, the consequences of supersonic trace velocities has been further developed in papers by Schmitz and Sim and their co-workers [9,10,11]. A key feature of all of this work on BVI is the prediction that the resulting noise radiation can be locally propagating in two dimensions rather than three.…”

Section: Introductionmentioning

confidence: 99%

Acoustic Kinematics of Helicopter BVI Noise

Lowson

2015

International Journal of Aeroacoustics

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Helicopter blade-vortex interaction (BVI) noise is known as a critical source of noise annoyance from helicopters. A key feature of the noise is that the trace velocities of the sources generated by the BVI process are supersonic, and thus have high radiation efficiency. This further means that noise is generated selectively by only a limited part of the overall interaction. The consequences of this have been studied using a simple cycloidal shed wake model. This allows the whole process to be explicitly described mathematically. The trace velocity can be infinite for both forward and retreating blades. This will generate strong noise radiation in directions which can be simply defined as a function of advance ratio. Analysis shows that many features are functions of rotor disc position only, independent of the number of rotor blades. This offers a helpful simplification. Radiation generates a series of caustics which can be defined by the analysis. Simplified models of the blade-wake interaction show that both the advancing and retreating blade interactions can generate cusps in the noise. Under some conditions these cusps are predicted to continue to the far field in the rotor disc plane, due to a kinematic balance of the change in propagation direction of the basic source vector and the change in the Mach angle of the principal radiation. This gives a two-dimensional decay in sound levels and will give rise to locally intense BVI field. The model also shows areas of the stronger noise fields will be generated in the direction of motion of the interacting blade. A detailed analysis has been undertaken for a four blade rotor at an advance ratio of 0.2. Multiple caustics from successive blade interactions can be identified, some of which have cusps. The analysis shows that the BVI radiation field can have large levels locally and helps to explain why helicopters are often perceived to be noisier than a simple dBA level might suggest. Each part of the rotor disc noise radiation to the far field can be related back to specific positions on the blade and specific parts of the shed wake. This offers the prospect of providing local adjustments to minimize BVI sources under particular conditions. All these results are based on the two dimensional cycloidal model. However it is believed that these effects must be reflected in more complex computer models and in real helicopters.The editor has modified the paper slightly − including some changes in notation − to address the minor concerns of the reviewers. At normal operating speeds the most intense source of noise arises from Blade Vortex Interaction (BVI) processes. The most intense source of helicopter noise is high speed impulsive noise. This is fundamentally due to blade thickness and compressibility effects. At the highest forward speeds this causes the direct radiation of noise by the advancing blade shock system, which has been found to extend outside the blade beyond "delocalization" speeds, typically around M = 0.9 for conventional rotors [1]. The intensity of ...

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Section: Introductionmentioning

confidence: 99%

Acoustic Kinematics of Helicopter BVI Noise

Lowson

2015

International Journal of Aeroacoustics

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“…Radiation directivity characteristics of BVI noise are determined to a first-order by the particular geometry and operating condition of the rotor system (Refs. 2,3). A straightforward way of minimizing BVI noise radiation is to operate the helicopter in such a way that the vortices trailed from the blades do not pass in close proximity to the following blades (Ref.…”

Section: Introductionmentioning

confidence: 99%

Quasi-Static Flight Path Control of Helicopter Blade Vortex Interaction Noise in a Steady Wind

Gopalan¹,

Schmitz²

2007

j am helicopter soc

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The effect of steady headwinds and tailwinds on helicopter Blade Vortex Interaction (BVI) ground-noise exposure levels is analytically investigated using a Quasi-Static Acoustic Mapping (Q-SAM) method. The analysis combines a quasi-static point performance model of an AH-1 helicopter with dipole acoustic modeling of BVI noise radiation to develop ground noise exposure trends during landing approaches under steady uniform longitudinal wind conditions. Two distinct landing approach procedures have been formulated, and their impact on ground noise exposure assessed. For the AH-1 helicopter, shallow, upwind and steep, downwind approaches can significantly reduce radiated BVI noise. The relative requirements of the resulting noise abatement landing trajectories are discussed. γ g inertial flight path angle (negative in descent) µ advance ratio, V / R µ a aerodynamic advance ratio, V a / R µ g "inertial" advance ratio, V g / R angular rotation rate of the main rotor

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“…T he num erical treatm en t of the blade-vortex interaction event varies in th e literatu re from aerodynam ic m odel building concepts, such as Schm itz et. al (2000) [7] (an extension of their own previous work [39]), and Berenger et. al (1997) [5], to thin-layer Navier-Stokes (Euler) equations [6,36,[43][44][45][46][47].…”

Section: 1 N U M E R Ic a L S Tu D Y O F B La D E (A Ir Fo Il)-v O mentioning

confidence: 99%

“…5 describes th e four types[39] of blade-vortex interactions which occur on the agsin'j(3.1) The M ach trace num ber describes th e local M ach num ber experienced by th e blade during the blade-vortex interaction, and depends on th e angle a t which th e rotor blade axis makes w ith th e vortex axis(7 ), th e azim uth angle of the blade (ipb) relative to th e free stream velocity (V^o), th e speed of sound (oq) and th e velocity of the point on th e P hase emissions of blade-vortex interaction waves in a single blade and tip vortex interaction[7].advancing side, as well as th e M ach trace num ber {Mtr) along th e non-dim ensional blade radius during each type of interaction. T he a -ty p e interaction experiences its peak effect a t approxim ately 70° azim uth and occurs m ainly near th e tip of the blade w ith little to no significant effect near the rotor hub.…”

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confidence: 99%

Particle image velocimentry measurements of an airfoil-vortex interaction event in a two-dimensional wind tunnel

Burwash¹

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P a r tic le Im a g e V e lo c im e tr y M e a su r e m e n ts o f an A irfo il-V o rtex In te r a c tio n E v en t in a T w o-D im e n sio n a l W in d T u n n el by W esley M. B u rw ash, B .S c. E ngin eerin g P h y sics A Thesis subm itted to the Faculty of G rad u ate Studies and Research in p a rtial fulfilment of th e requirem ents for the degree of M a ster o f A pp lied Science in A erosp ace E ngineering O ttaw a-C arleton In stitu te for M echanical and Aerospace Engineering D epartm ent of M echanical and Aerospace Engineering

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Radiation and directionality characteristics of advancing side blade-vortex interaction (BVI) noise

Cited by 13 publications

References 7 publications

Acoustic Kinematics of Helicopter BVI Noise

Acoustic Kinematics of Helicopter BVI Noise

Quasi-Static Flight Path Control of Helicopter Blade Vortex Interaction Noise in a Steady Wind

Particle image velocimentry measurements of an airfoil-vortex interaction event in a two-dimensional wind tunnel

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