Inlet shape effects on the far-field sound of a model fan

Clark, L. R.; Thomas, Russell H.; Dougherty, Robert P.; Farassat, F.; Gerhold, Carl H.

doi:10.2514/6.1997-1589

Cited by 15 publications

(6 citation statements)

References 8 publications

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“…For example, as aforementioned in Sect. 1, the study presented in [7] showed that sound sideline directivity can be affected up to 8 dB by the inlet shape, and the work of [8] whose results indicated a 10 dB rise of the broadband levels when the inlet turbulence level increases from 2 to 8%. This issue was also addressed in [50], evidencing interference effects on noise measurements due to the presence of the ICD and measurement probes located upstream of the rotor.…”

Section: Comparison Of Noise Computation By Lbm and Fw-hmentioning

confidence: 96%

“…Nonuniform inflow can be produced by many different factors such as position of the temperature sensor at the inlet, turbulent boundary layer on the casing wall, atmospheric turbulence, inclined inflow due to inclination of the fan axis relative to the flow. For example, the study presented in [7] shows that small changes of the inlet shape of the nacelle affect the sideline tonal noise level up to 8 dB. In addition, the numerical work of [8] shows that the turbulence intensity level of the incoming flow influences significantly the noise generated, as much as an increase of 10 dB when comparing the noise generated from a low turbulent inflow case with a highly turbulent inflow configuration.…”

Section: Introductionmentioning

confidence: 98%

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Noise predictions of the advanced noise control fan model using lattice Boltzmann method and Ffowcs Williams–Hawkings analogy

Orselli

Carmo

Queiroz

2018

J Braz. Soc. Mech. Sci. Eng.

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The lattice Boltzmann method (LBM) is applied to simulate the complete three-dimensional transient flow and noise generated on the Advanced Noise Control Fan (ANCF) geometry. The ANCF is a model developed by NASA Glenn composed by a rotor-stator system enclosed by a duct. The experimental noise spectra provided by NASA at 30 microphones around the fan are used to validate the results obtained with the LBM. Overall, the predicted sound spectra pattern and the main tonal frequencies agree well with the noise measurements; in terms of tonal noise levels, the agreement varies depending on the frequency and microphone position. The noise at the 30 microphone positions is also computed by employing the porous Ffowcs Williams and Hawkings (FW-H) formulation with noise sources located on two integral surfaces placed at the ANCF openings. The good agreement obtained between the sound levels calculated with the FW-H formulation and those computed by the LBM show that the FW-H analogy may be applied in place of the LBM numerical simulation. In addition, the FW-H formulation is applied to compute the sound generation with sources located on different physical surfaces of the ANCF model such as the rotor, stator, hub, and nacelle, procedure known as noise source breakdown. A comparison of the FW-H results applied on different surfaces of the ANCF model with the noise computed by the LBM shows that most of the tonal noise levels observed at the far-field microphones (predicted by the LBM simulation) correspond to the noise sources generated on the stator vane surfaces. Such a study of the noise sources breakdown also evidences the interaction effect between the rotor and the stator, whose mechanism is the main contributor to the tonal noise generation content.

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Section: Comparison Of Noise Computation By Lbm and Fw-hmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 98%

Noise predictions of the advanced noise control fan model using lattice Boltzmann method and Ffowcs Williams–Hawkings analogy

Orselli

Carmo

Queiroz

2018

J Braz. Soc. Mech. Sci. Eng.

View full text Add to dashboard Cite

show abstract

“…With these models in hand, it is useful to compare with other experiments, certain aspects of which make their results unsuitable for model development, but which may still serve as a qualitative check on the general aspects of the model. Clark et al [28] tested a 10% scale model of the Pratt and Whitney Advanced Ducted Propeller (ADP) with several inlet shapes (short, long, scarfed, and elliptical) in the NASA Langley 14-by 22-Foot Subsonic Tunnel. The different inlet shapes caused nonuniformity of the inlet boundary layer thickness that led to unsteady forces on the fan that propagated as increased fan noise over the entire acoustic measurement region.…”

Section: Turbulence Ingestionmentioning

confidence: 99%

“…To model the higher harmonics (up to 4BPF), the noise levels are subtracted by 3 dB for each harmonic to model a decreasing effect of BLI with increasing BPF harmonic. Limited data from Jones et al [26], Clark et al [28], and Koch [29] suggest that higher harmonics are affected by nearly the same amount as the fundamental tone, but because these data are more limited and less applicable to the physical scenario at hand, the use of a 3 dB subtraction for each harmonic represents a conservative choice to predict this effect.…”

Section: Mean Flow Distortionmentioning

confidence: 99%

Aircraft System Noise Assessment of the NASA D8 Subsonic Transport Concept

Clark

Thomas

Guo³

2018

2018 AIAA/CEAS Aeroacoustics Conference

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A vehicle-level noise assessment has been performed for the NASA D8 concept aircraft (ND8) in the NASA Advanced Air Transport Technology Project portfolio. The NASA research-level Aircraft NOise Prediction Program (ANOPP-Research) was used to predict the noise from each source component on the ND8 to build up a noise estimate for the full aircraft. The propulsion airframe aeroacoustic (PAA) effects of the ND8, namely boundary layer ingestion (BLI) with its influence on fan noise, and the noise shielding, reflection, and diffraction mechanisms of the unconventional airframe, were empirically modeled using experimental data. Noise reduction technologies appropriate to the 2025-2035 time frame were included in this study. Including all technologies and PAA effects, the ND8 is predicted to have a cumulative margin to the Stage 4 certification metric of only 7.4 EPNdB. Boundary layer ingestion is predicted to have a detrimental impact on cumulative noise levels on the order of 15 EPNdB. Fan noise is seen to be the primary noise source at all three certification points, even if the BLI noise impact could be entirely suppressed. The impact of engine noise shielding by the airframe is limited by a lack of aft shielding and the presence of horizontal tail reflections in the aft direction. The physical constraint on engine size by the pi-tail is seen as a potential barrier to engine noise reduction through the corresponding limitation on fan bypass ratio. Mildly reduced climb performance (compared to similar reference aircraft) does not provide any benefit through increased noise propagation distance. If the boundary layer ingestion noise penalty could be suppressed such that BLI would have no effect on noise, the cumulative margin to Stage 4 would increase to 22.4 EPNdB, still below the NASA Mid Term goal of 32-42 EPNdB.

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“…In addition to developing quieter engines and airframe systems, an approach that is considered in the design of quieter aircraft is the shielding of noise components. For example, engines can be placed above an aircraft wing or fuselage to partially shield engine noise radiation, or the lower side of the inlet of an engine can be extended forward (scarf inlet 1 ) to reflect inlet noise away from the ground. This approach to noise reduction has been the subject of growing interest [2][3][4][5][6][7] which has revealed a need for further validation and improvement of current noise scattering prediction tools.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study of Noise Shielding by a NACA 0012 Airfoil

Hutcheson

Bahr

Thomas

et al. 2018

2018 AIAA/CEAS Aeroacoustics Conference

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The effects of sound source location, Mach number and angle of attack on the shielding of a laser-induced sound source by a NACA 0012 airfoil are examined. The sound source is a small plasma generated by a high energy, laser beam focused to a point. In-flow microphone measurements are acquired in the midspan plane of the airfoil over a broad range of streamwise stations, and shielding levels are calculated over different frequency ranges from the measurements acquired with and without the airfoil installed. Shielding levels are shown to increase as the source is positioned closer to the mid-chord of the airfoil, and to significantly decrease with increasing flow Mach number, except when the source is positioned near the leading edge of the airfoil. Both with and without flow, changes in angle of attack are associated with a corresponding shift of the shadow region. Finally, the effects of multipath signals, observer distance and signal scatter on the measured shielding levels are discussed.

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Inlet shape effects on the far-field sound of a model fan

Cited by 15 publications

References 8 publications

Noise predictions of the advanced noise control fan model using lattice Boltzmann method and Ffowcs Williams–Hawkings analogy

Noise predictions of the advanced noise control fan model using lattice Boltzmann method and Ffowcs Williams–Hawkings analogy

Aircraft System Noise Assessment of the NASA D8 Subsonic Transport Concept

Experimental Study of Noise Shielding by a NACA 0012 Airfoil

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