Inclusion of Broadband Shock-Associated Noise in Spectral Decomposition of Noise from High-performance Military Aircraft

Abstract

Attempts to reduce the noise from high-performance military aircraft requires an understanding of the different jet noise generation mechanisms. The primary noise sources originate from interactions between turbulent mixing noise associated with large and finescale turbulent structures and the ambient air. A nonideally expanded jet also contains broadband shock-associated noise. A three-way decomposition of the spectral density measured near a tied-down F-35B quantifies the contribution from each type of noise. The decomposition is performed on noise from a ground-based, linear array of microphones, approximately 8 m from the estimated shear layer, which spanned an angular aperture of 35° to 152° (relative to engine inlet). This large spatial aperture allows for a detailed investigation into the spatial variation in broadband shock-associated noise and fine and large-scale turbulent mixing noise. The spectral decompositions match the measured spectral levels with three main exceptions: 1) the F-35B noise contains multiple spectral peaks in the maximum radiation region, 2) nonlinear propagation increases the high-frequency spectral levels, and 3) the low-frequency levels in the maximum radiation region are less than those predicted by the large-scale similarity spectrum. The main peak of the F-35B broadband shock-associated noise, evident from 35°-70°, has the same characteristic shape and variation in peak frequency as overexpanded, laboratory-scale jets. The F-35B broadband shockassociated noise peak level and width exhibit different trends than laboratory-scale BBSAN and those recently reported for the F/A-18E [

Dependence of High-performance Military Aircraft Noise on Frequency and Engine Power

“…The directivity angle of BBSAN noise increases with frequency across all engine conditions, which is consistent with laboratory-scale overexpanded jets [32], as well as conclusions for this aircraft by Ref. [12].…”

“…For engine conditions at 75% ETR and above, radiation in the forward direction is observed between 300-700 Hz, which analyses in Refs. [12,13] show to be BBSAN.…”

“…Multilobe radiation is a feature of military aircraft jet noise that is seen in several datasets [7,[10][11][12][13][14][15][16][17], though no conclusive explanation of its cause has been given. These lobes are described as either multiple peaks in the spectra at a given measurement location or as multiple local maxima in space across the array when plotting a single frequency.…”

Análisis del factor ruido en las actividades de mantenimiento aeronáutico militar.

“…Conforme a la figura 6 y tabla 4, el nivel más alto de ruido en el presente estudio, se registra en las actividades de mantenimiento de la aviación supersónica, alcanzando un LAeqD de 105 dB, en donde 5 datos que corresponden al 33.33 %, superan los 85 dB, de los cuales 4 registros corresponden al pre vuelo o despacho de la aeronave (DA) y un solo valor corresponde al funcionamiento de la planta para enfriamiento (PEE) con 89 dB; resultados que no superan al encontrado por Corbalán et al (2019), en el momento de despegue de una aeronave de este tipo, no obstante son comparables a los 100 dB determinados en Neilsen et al (2018), pues fueron obtenidos en la línea de vuelo o plataforma, en el despacho de la aeronave (DA).…”

“…En lo referente al área de mantenimiento de aeronaves de igual forma tiene sus particularidades debido al tipo de fuente generadora de ruido, ya que por una parte se usan maquinarias y equipos diferentes a otras áreas industriales, así como también, la aeronave se convierte en ciertas ocasiones en la generadora de ruido, como es en el caso de despacho, recepción, o prueba de motores, en las cuales el personal técnico está expuesto a importantes niveles de contaminación sonora que alcanzan los 100 dB (Neilsen et al, 2018) y superando los 140 dB en el caso de aeronaves supersónicas (Corbalán, Trujillo, Szajderman, & Di Bernardi, 2019), no obstante, de acuerdo con Caputo & Correa (2018), con el uso adecuado de elementos de protección auditiva, se logra una reducción que va desde los 20 dB hasta los 40 dB, dependiendo de la calidad y clase de equipo utilizado.…”