This paper aims to identify the attributes that describe aircraft interior noise, determine most important psychoacoustic models that characterize cabin sounds, and construct a prediction model that can be utilized for VIP and business jets to evaluate subjective perception. In the first part, paired comparison listening tests and free verbalization are conducted with expert subjects who experienced VIP and business aircraft flight. The study generated a list of adjective pairs that describe perception of cabin sounds to be used for semantic differential listening tests. Multi-dimensional scaling is performed on paired comparison data. Results showed that subjects’ decisions can be categorized in loudness and annoyance dimensions which are not necessarily linearly associated. The second part of the study is the development of a sound quality prediction model for aircraft cabin. Semantic differential tests are conducted with potential customers. Objective sound quality metrics are correlated to subjective test responses using principal components regression. This model is found to be most effective explaining pleasantness, comfort, and loudness perception. It is intended to be utilized to modify/redesign noise control treatments and sound signature of an aircraft. All listening tests were conducted inside an aircraft cabin simulator considering the influence of visual content.

The negative impact of aircraft noise includes effects on population’s health, land use planning and economic issues such as building restrictions and operating restrictions for airports. Thus, the reduction of noise generated by aircraft at take-off and approach is an essential consideration in the development of new commercial aircraft. Among the different aircraft noise sources, landing gear noise is one of the most significant during approach. This research presents results from the European Clean Sky funded ALLEGRA project, which investigated a full-scale Nose Landing Gear (NLG) model featuring the belly fuselage, bay cavity and hydraulic dressing. Tests were performed for a variety of wind speeds and yaw angles. In this paper, a characterization of the noise generated by the full-scale Nose Landing Gear (NLG) model is presented and the different techniques used for characterizing acoustic sources on the NLG are described. The landing gear noise source is characterized in terms of OASPL, directivity, source spectra, PNL and PNLT. A comparison between the NLG with and without the application of low noise technology is presented.

The reduction of noise generated by aircraft at take-off and approach is crucial in the design of new commercial aircraft. Landing gear noise is significant contribution to the total noise sources during approach. The noise is generated by the interaction between the non-aerodynamic components of the landing gear and the flow, which leads to turbulence generated noise. This research presents results from the European Clean Sky funded ALLEGRA project. The project investigated a full-scale Nose Landing Gear (NLG) model featuring the belly fuselage, bay cavity and hydraulic dressing. A number of low noise treatments were applied to the NLG model including a ramp door spoiler, a wheel axel wind shield, wheel hub caps and perforated fairings. Over 250 far field sensors were deployed in a number of microphone arrays. Since technologies were tested both in isolation and in combination the additive effects of the technologies can be assessed. This study describes the different techniques used to quantify the contribution of each technology to the global noise reduction. The noise reduction technologies will be assessed as a function of frequency range and through beamforming techniques such as source deletion.

The coupled panel cavity system composed of an acoustic space and a wall surface is a reasonable representation of many engineering applications. A good understanding of the structural-acoustic interaction between the structural vibration and sound pressure response inside the cavity is of critical importance to, for instance, the control of sound fields in car compartments, airplane and ship cabins, etc. Motivated by above, an investigation on the structural-acoustic responses of a coupled panel cavity system is presented. A rectangular acoustic cavity bounded by a flexible panel with elastically restrained edges is examined. In this paper, for the so called “mid-frequency” problem, a hybrid deterministic and statistic approach is employed to overcome the defects in application of pure deterministic or statistical methods. Then the vibration and interior sound pressure response analysis for the panel-cavity system are conducted using this method under external normal concentrated force acting at the flexible plate. Finally, comparisons between the numerical and test results are presented and the relevant frequency ranges for which the hybrid deterministic and statistical approaches work in are discussed for the given structure.

This paper presents a methodology to obtain the day-night average sound pressure levels DNL from continuous measurements. The methodology is used for processing data acquired during 3 days of the summer of 2011 at a point located 9,500 meters to the south of the SCEL airport in Santiago of Chile, considering the unique contribution of aircraft noise. Additionally, this measured DNL is compared with a modeling performed for the same point via the software Integrated Noise Model version 7.0b. Finally, using the model settled, a calculation was made to find values of DNL on the same points where measurements were made in 2003 under the Environmental Impact Assessment for the second runway of the SCEL Airport. The results were compared and discussed.

Noise propagation mechanisms in presence of a rotational flow are currently receiving some attention from the aircraft industry. Different methods are used in order to compute the acoustic wave propagation in sheared flows in terms of pressure perturbations (e.g. Linearized Euler Equations (LEE), Lilley’s and Galbrun’s equations). Nevertheless, they have drawbacks in terms of computational performance (high number of DOFs per node, inadequacies of classical numerical schemes like standard FE). In contrast with other studies, in this work, the fluctuating total enthalpy is selected as the main variable in order to describe the acoustic field, which obeys to a convected wave equation obtained by linearization of momentum (Crocco’s form), energy and continuity equations and with coefficients depending on flow variables. The resulting 3D convected wave operator is an extension of the Möhring acoustic analogy which is able to predict the sound propagation through rotational flows in the subsonic regime and is well adapted to FE discretization. A 2D convected wave equation is generated from the previous operator. This is followed by a numerical solution based on FEM with two types of boundary conditions: non reflecting BC and incident plane wave excitation. The numerical results are used to estimate the reflection coefficient generated by the shear flow. The new acoustic wave operator is compared to well-known theories of flow acoustics (Pridmore-Brown wave operator) and shows promising results. Finally additional development steps are presented so further improvements on the new operator can be carried out.

This paper presents beamforming techniques for source localization on aicraft in flight with a focus on the development at DLR in Germany. Fly-over tests with phased arrays are the only way to localize and analyze the different aerodynamic and engine sources of aircraft in flight. Many of these sources cannot be simulated numerically or in wind-tunnel tests because they they are either unknown or they cannot be resolved properly in model scale. The localization of sound sources on aircraft in flight is performed using large microphone arrays. For the data analysis, the source signals at emission time are reconstructed from the Doppler-shifted microphone data using the measured flight trajectory. Standard beamforming techniques in the frequency domain cannot be applied due transitory nature of the signals, so the data is usually analyzed using a classical beamforming algorithm in the time domain. The spatial resolution and the dynamic range of the source maps can be improved by calculating a deconvolution of the sound source maps with the point spread function of the microphone array. This compensates the imaging properties of the microphone array by eliminating side lobes and aliases. While classical beamfoming yields results that are more qualitative by nature, the deconvolution results can be used to integrate the acoustic power over the different source regions in order to obtain the powers of each source. ranking of the sources. These results can be used to rank the sources, for acoustic trouble shooting, and to assess the potential of noise abatement methods.

Blast noise from military installations often has a negative impact on the quality of life of residents living in nearby communities. This, in turn, negatively impacts the military’s testing & training capabilities due to restrictions, curfews, or range closures enacted to address noise complaints. In order to more directly manage noise around military installations, accurate noise monitoring around bases has become a necessity. Although most noise monitors are simple sound level meters, more recent ones are capable of discerning blasts from ambient noise with some success. Investigators at the University of Pittsburgh (Pitt) developed a more advanced noise classifier that can discern between wind, aircraft, and blast noise, while simultaneously lowering the measurement threshold. Here, more recent work between Pitt and the US Army Engineer Research and Development Center will be presented from the development of a more advanced classifier that identifies additional classes of noise such as machine gun fire, vehicles, and electronic noise. Additional signal metrics were explored given the increased complexity of the classifier. By broadening the types of noise the system can accurately classify and increasing the number of metrics, a new system was developed with increased blast noise accuracy, decreased number of missed events, and significantly fewer false positives.

The turbulent boundary layer that forms on the outer surfaces of vehicles can be a significant source of interior noise. In automobiles this is known as wind noise, and at high speeds it dominates the interior noise. For airplanes the turbulent boundary is also a dominant noise source. Because of its importance as a noise source, it is desirable to have a model of the turbulent wall pressure fluctuations for interior noise prediction. One important parameter in building the wall pressure fluctuation model is the convection velocity. In this paper, the phase velocity was determined from the streamwise pressure measurements. The phase velocity was calculated for three separation distances ranging from 0.25 to 1.30 boundary layer thicknesses. These measurements were made for a Mach number range of 0.1 < M < 0.6. The phase velocity was shown to vary with sensor spacing and frequency. The data collapsed well on outer variable normalization. The phase velocities were fit and the group velocity was calculated from the curve fit. The group velocity was consistent with the array measured convection velocities. The group velocity was also estimated by a band limited cross correlation technique that used the Hilbert transform to find the energy delay. This result was consistent with the group velocity inferred from the phase velocities and the array measured convection velocity. From this research, it is suggested that the group velocity found in this study should be used to estimate the convection velocity in wall pressure fluctuation models.

This paper deals with the effects of atmospheric absorption on the propagation of high-speed jet noise. The common practice for determining the far-field jet noise spectra at a distance far from the jet exit (>100D, where D is the nozzle exit diameter) involves extrapolating data that is typically obtained between 35D and 100D from the nozzle exit. The data is extrapolated along a radial line from the nozzle exit by accounting for the effects of spherical spreading and atmospheric absorption. A previous paper discussed far-field measurements that were obtained for a twin engine aircraft at three locations along a radial line in the peak noise radiation direction. The authors were unable to extrapolate the spectra from the nearest location to either of the further locations and the observed differences were attributed to nonlinear effects in the jet noise signal. It is the purpose of this paper to show that the common extrapolation practice is valid for high speed jets, except in the peak radiation direction and its surrounding angles. Mach wave radiation is present at these locations and the common practice will yield unsatisfactory results, similar to those observed in the previous paper. The data used in this paper is taken from experiments carried out at 1/5th-scale and full scale and the experimental conditions of these high-speed jets are quite similar to those of the previous paper.