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

Gopalan, Gaurav; Schmitz, Fredric H.

doi:10.4050/jahs.52.15

Cited by 9 publications

(8 citation statements)

References 7 publications

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“…The code, based on the Quasi-Static Acoustic approach [27,28], considers an acoustic database (ADB) as input and propagates the acoustic field on the ground through a ray tracing technique. The ADB is made up of far-field acoustic hemispheres, computed by the above-mentioned propagation model, able to reproduce the acoustic source in terms of three-dimensional directivity pattern and covering the whole trimming conditions needed during the flight trajectory.…”

Section: Ground Propagation Noise Modelmentioning

confidence: 99%

Aeroacoustics Assessment of an Hybrid Aircraft Configuration with Rear-Mounted Boundary Layer Ingested Engine

2021

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Hybrid electric propulsion is a promising solution to reduce aircraft emissions, thus improving the sustainability of the air transport. In this work, a hybrid aircraft configuration with a rear-mounted boundary layer ingestion (BLI) engine has been investigated. The partial embedding of the engine into the fuselage generates a distortion of the ingested inflow causing additional tonal and broadband BLI noise sources, and, at the same time, alters the existing one, such as the rotor–stator interaction noise (RSI). This work is focused on the tonal RSI noise modeling, with and without the distortion generated by the BLI, and the far-field propagation including the acoustic masking contribution due to the engine–fuselage integration. As the main result, this work shows the contributions of BLI and the engine–aircraft integration on the RSI noise. Both effects should be properly taken into account in the early aircraft design stage for an effective noise reduction even at ground level.

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Section: Ground Propagation Noise Modelmentioning

confidence: 99%

Aeroacoustics Assessment of an Hybrid Aircraft Configuration with Rear-Mounted Boundary Layer Ingested Engine

2021

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“…For this case, all six vehicle equilibrium equations are used (rather than just the equilibrium of forces in the X-direction, as previously done (Refs. [15][16][17][18]), so the effect of introducing an X-force is more rigorously modeled.…”

Section: Introductionmentioning

confidence: 99%

“…A related concept for BVI noise reduction involves the modification of the vehicle trim, specifically the longitudinal rotor disk tilt, during descent through the introduction of an X-force (Refs. [15][16][17][18]. The change in the rotor disk tilt affects the net flow velocities through the rotor and can increase the blade-vortex miss-distances.…”

Section: Introductionmentioning

confidence: 99%

“…Also, in contrast to the previous analytical studies on X-force control (Refs. [15][16][17][18], a freewake analysis is used in conjunction with a rotor aeroelastic model so that the positions of the vortices relative to the blades and the unsteady impulsive loading that produces the BVI noise can be determined accurately. The study comprises of two parts.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of Helicopter Blade-Vortex Interaction Noise with Flight Path or Attitude Modification

Munsky¹,

Gandhi²

2005

j am helicopter soc

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This study examines the effects of flight-path modification and attitude modification through the introduction of an X-force on helicopter blade-vortex interaction (BVI) noise in low-speed descent.A free-wake analysis is used in conjunction with a rotor aeroelastic model, to accurately determine the positions of the vortices relative to the blades and the unsteady impulsive BVI loading. The aeroacoustic code WOPWOP is used to calculate the resulting BVI noise. The results in the present study indicate that while regimes of high BVI noise show general qualitative correlation to regimes of zero inflow from simple momentum theory based analyses, the maximum noise levels are actually seen at different advance ratio and rotor disk tilt combinations from those at which momentum theory predicted zero mean inflow. As the rotor shaft angle is varied (corresponding to change in descent rate) different advancing side BVI events become dominant, even as others recede in importance. Thus, small to moderate changes in shaft angle have little effect in reducing the total BVI noise. It is also seen that as different BVI events become dominant, the directionality of the total radiated noise changes. An X-force in the drag direction tilts the rotor disk forward, convects the vortices lower relative to the baseline. In contrast, a propulsive X-force convects the vertices upward relative to the baseline. For a high-noise baseline condition, with one or more parallel vortices in the rotor plane either a propulsive or drag X-force does not, in equal measure, reduce noise. This is again related to different interactions dominating for different levels of X-force; these changes depend on the flight path. Thus, while a drag force was found to reduce BVI noise for a 0.1875 advance ratio moderate glide path, a propulsive force was found to be beneficial for the same advance ratio and a steeper glide path. This makes exploiting the X-force control concept more challenging. Even so, reductions of more than 10 dB in peak BVI noise levels certainly appear to be possible using X-force levels of the order of about 5% of the vehicle weight.

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“…32 They used the idea that the conservation laws in differential form are also valid when all ordinary derivatives are viewed as generalized derivatives, which, when applied to general surfaces in motion, provide a governing equation which is more useful in rotor noise prediction.…”

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confidence: 99%

In-Flight Array Measurements of Tail Rotor Harmonic Noise

Sargent¹,

Schmitz²,

Sim³

2010

j am helicopter soc

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Acoustic data that utilized a unique flying microphone boom array was analyzed using a time domain averaging technique, based on a theoretical tail rotor one-per-rev signal, to obtain tail rotor acoustic time histories for forward and descending flight. This flying microphone array approach provides useful insight into the directivity and noise mechanisms associated with the periodic harmonic noise generated by the Bell 206B tail rotor. Comparisons between linear harmonic noise theory and the time averaged data show good agreement, indicating that the average harmonic noise of the 206B is dominated by thickness noise near the tip-path-plane of the tail rotor and by loading noise at the out-of-plane microphone positions. The measured data also provides trends in the overall sound pressure level (OASPL) with respect to both forward velocity and descent angle. A significant deviation from the average SPL of the harmonic noise levels at high frequencies is also shown.

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

Cited by 9 publications

References 7 publications

Aeroacoustics Assessment of an Hybrid Aircraft Configuration with Rear-Mounted Boundary Layer Ingested Engine

Aeroacoustics Assessment of an Hybrid Aircraft Configuration with Rear-Mounted Boundary Layer Ingested Engine

Analysis of Helicopter Blade-Vortex Interaction Noise with Flight Path or Attitude Modification

In-Flight Array Measurements of Tail Rotor Harmonic Noise

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