Aircraft noise

About: Aircraft noise is a research topic. Over the lifetime, 3051 publications have been published within this topic receiving 32039 citations.

Flight Effects on Supersonic Jet Noise from Chevron Nozzles

Abstract: Currently tactical aircraft supersonic jet noise studies are conducted at near static conditions motivated by the need to develop nozzle concepts for mitigating aircraft carrier launch crew noise levels. Effects of forward flight on supersonic jet noise source mechanisms need to be included as the next step to demonstrating concept benefits for community noise reduction during training scenarios where aircraft operate from land based airfields. Hence, the current study was directed at the flight effects on far field noise from round and chevron nozzles in model scale experiments conducted in the United Technologies Research Center (UTRC) open jet acoustic wind tunnel. The objective was to document the statistical characteristics of the noise at tunnel Mach numbers up to Mt =0.4 since there is limited generic data for military engine supersonic exhaust conditions under such forward flight scenarios. The study focuses on the noise characteristics in the aft quadrant which dominates the tactical aircraft noise signature. A generic chevron nozzle, developed for noise reduction, was included in the evaluation as part of tracking the noise reduction consistency with increasing forward flight. The chevron geometry consisted of the baseline shock-free round nozzle with 12 chevrons attached at the nozzle exit. Exit diameter corresponded to 2” for both nozzles. Static temperature ratios ranged from isothermal to Tr =2. The impact of chevrons on impulsive signature skewness reduction was tracked in the acoustic far field at near static conditions. Both the round and chevron nozzle were also operated at off-design conditions with over and underexpanded nozzle pressure ratios (NPR) for the skewness study.

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

Abstract: To further understand the unique characteristics of military aircraft noise, the sound field in the vicinity of a tied-down F-35B was measured for various engine powers, from 25% to 150% Engine Thrust Request (ETR). Synchronous measurements along a linear ground array approximately parallel to the shear layer were used to image the entire field through multisource statistically optimized near-field acoustical holography (M-SONAH). The field in the direction of maximum radiation consists of multiple lobes in the spatiospectral domain, which are manifest as multiple local maxima in space for a fixed frequency or multiple peaks in the spectra at a fixed location. Multiple lobes are observed at non-afterburning and afterburning engine conditions. As frequency increases for a given engine power, lobes appear towards the sideline and shift aft until they disappear beyond the measurement aperture and new lobe(s) take their place. As engine power is increased at a fixed frequency, the forwardmost lobe increases in its relative contribution to the field, which is a major contributing factor to the forward shift in overall directivity with increasing engine power. Field reconstructions and data in the forward direction outside of the region of maximum radiation show the presence of broadband shock-associated noise (BBSAN) for 75% ETR and above. Reconstructions along the nozzle lipline of the jet indicate the BBSAN originates from approximately the same region as the sources for the main radiation direction

Aircraft Noise Model Validation

Abstract: Aircraft noise models are now used widely by a large number of countries. Models vary in detail depending upon the needs of their users. Increasingly, models are becoming more sophisticated as additional needs develop. Traditionally noise models have been used to depict long-term historical noise exposure. However, they are often used to assess noise mitigation options and other ‘what if’ type scenarios. These applications have meant that a number of noise models have been subject to close scrutiny by interested parties, spurring further validation and model development studies. Throughout the paper, the various techniques and methods are illustrated using data from a recent UK study of approach noise at London Heathrow airport. The deficiencies with present noise modelling techniques such as lateral attenuation are discussed and possible options for future development are considered.