Search

NASA is building the X-59 Quiet Supersonic Technology aircraft to produce low noise sonic booms for a series of community noise surveys across the USA. Survey participants will rate their perception of the lowbooms from supersonic X-59 flyovers. Several noise metrics are proposed to quantify the noise dose: A-, B-, D-, and E-weighted Sound Exposure Level, Stevens Perceived Level, and Indoor Sonic Boom Annoyance Predictor. Sparse measurements across the survey area will be used to estimate community noise exposure. The level of these low-booms may be comparable to the ambient noise level in some locations, leading to uncertainty in noise exposure estimations. A linear relationship between A-weighted ambient levels and sonic boom metric levels is assumed and determined using measured ambient levels. The resulting relationship is then used to express the National Park Service’s A-weighted L50 SPL map in terms of sonic boom metric levels because A-weighted L50 SPL is not typically used to describe sonic booms. These nationwide estimates of ambient levels will aid in X-59 community test planning. The signal-to-noise ratio for the undertrack X-59 sonic boom is also estimated, and an example application is presented for comparing potential noise monitor sites prior to a community noise test. [ABSTRACT FROM AUTHOR]

In the efforts to reduce the intensity of sonic boom generated by a supersonic aircraft, the problem of measuring the parameters of the shock waves in the experiments in a non-uniform flow is considered. It is necessary to measure the static pressure distribution behind the head shock wave at various distances from the model under study. The measured data of the shock wave profile obtained with the help of a drained measuring plate and a comb of pressure probes are given. A technique for processing experimental data is presented. [ABSTRACT FROM AUTHOR]

The level of the sonic boom forming on the Earth surface which is negative for the environment is an important challenge related with the potential usage of the SCA (supersonic civil aircraft). Creation of the SCA configuration with the decreased level of the sonic boom involves the investigations of the influence of the aircraft elements and their position on the forming disturbed pressures in the near zone and their propagation over big distances from the source [1]. [ABSTRACT FROM AUTHOR]

The sonic boom generated by a slender body of revolution with an aerodynamic surface placed upstream of the body is numerically investigated. A thin disk placed upstream of the body in supersonic free-stream flow is used as the aerodynamic surface. A combined method of phantom bodies is used for sonic boom calculations. The method is tested by calculating the sonic boom generated by a blunted body and comparing the results with experimental investigations of the sonic boom generated by spheres of various diameters in ballistic ranges and wind tunnels. The test calculations show that the method of phantom bodies is applicable for calculating far-field parameters of shock waves generated by both slender and blunted bodies. A possibility of reducing the shock wave intensity in the far field is estimated. The calculations are performed for the incoming flow with the Mach number equal to 2. The angle of attack of the disk, the disk size and its position upstream of the slender body are varied in the calculations. [ABSTRACT FROM AUTHOR]

The method for simultaneous measurement of pressure and average mass flow rate in the dynamic recording mode in the conditions of the T-313 wind tunnel of ITAM SB RAS is presented. Experimental studies were carried out in the mode M = 2.04, Re1 = (15-25)·106, and T0 = 283 K. Measurement was carried out in the near field of a sonic boom. Distributions of average mass flow rate were measured using a constant-resistance thermoanemometer CTA-2016 (v.2). [ABSTRACT FROM AUTHOR]

One goal of NASA's Commercial Supersonic Technology Project is to identify candidate noise metrics suitable for regulating quiet sonic boom aircraft. A suitable metric must consider the short duration and pronounced low frequency content of sonic booms. For indoor listeners, rattle and creaking sounds and floor and chair vibrations may also be important. The current study examined the effect of such vibrations on the annoyance of test subjects seated indoors. The study involved two chairs exposed to nearly identical acoustic levels: one placed directly on the floor, and the other isolated from floor vibrations by pneumatic elastomeric mounts. All subjects experienced both chairs, sitting in one chair for the first half of the experiment and the other chair for the remaining half. Each half of the experiment consisted of 80 impulsive noises played at the exterior of the sonic boom simulator. When all annoyance ratings were analyzed together there appeared to be no difference in mean annoyance with isolation condition. When the apparent effect of transfer bias was removed, a subtle but measurable effect of vibration on annoyance was identified. [ABSTRACT FROM AUTHOR]

Aircraft manufacturers are interested in designing and building a new generation of supersonic aircraft that produce shaped sonic booms of lower peak amplitude than booms created by current supersonic aircraft. To determine if the noise exposure from these "low" booms is more acceptable to communities, new laboratory testing to evaluate people's responses must occur. To guide supersonic aircraft design, objective measures that predict human response to modified sonic boom waveforms and other impulsive sounds are needed. The present research phase is focused on understanding people's reactions to booms when heard inside, and therefore includes consideration of the effects of house type and the indoor acoustic environment. A test was conducted in NASA Langley's Interior Effects Room (IER), with the collaboration of NASA Langley engineers. This test was focused on the effects of low-frequency content and of vibration, and subjects sat in a small living room environment. A second test was conducted in a sound booth at Purdue University, using similar sounds played back over earphones. The sounds in this test contained less verylow- frequency energy due to limitations in the playback, and the laboratory setting is a less natural environment. For the purpose of comparison, and to improve the robustness of the model, both sonic booms and other more familiar transient sounds were used in the tests. The design of the tests and the signals are briefly described, and the results of both tests will be presented. [ABSTRACT FROM AUTHOR]

Various sonic boom noise metrics have been calculated for a number of sonic boom, N-wave signatures. The newly computed metrics dataset utilized high-quality recordings from the Superboom Caustic Analysis and Measurement Program (SCAMP) experiment conducted by NASA. With this signature dataset comprised of microphone measurements by long linear arrays, one can assess the waveform variability due to atmospheric turbulence influences across the arrays. Preferred boom events from these NASA datasets were then chosen after review of the flight conditions, flight objectives and actual waveforms generated in order to study only the non-focused, N-wave sonic boom signatures. The sonic boom noise metrics calculated for the preferred boom events include Stevens Mark VII Perceived Level (PLdB), un-weighted Sound Exposure Level (SELz) as well as Sound Exposure Level with A, B, C, D, and E weightings applied to the waveforms. The results show, for example, that the A-weighted sound exposure levels and Steven's Mark VII Perceived Levels had standard deviations in the range of 1.4 dB to 6.1 dB for the SCAMP measurements. Such sensitivity results should be helpful in assessing the applicability of sonic boom metrics for use in future en-route certification standards for civilian supersonic aircraft. [ABSTRACT FROM AUTHOR]

A pool of 240 subjects was exposed to a library of waveforms consisting of example signatures of low boom aircraft. The signature library included intentional variations in both loudness and spectral content, and were auralized using the Gulfstream SASS-II sonic boom simulator. Post-processing was used to quantify the impacts of test design decisions on the "quality" of the resultant database. Specific lessons learned from this study include insight regarding potential for bias error due to variations in loudness or peak over-pressure, sources of uncertainty and their relative importance on objective measurements and robustness of individual metrics to wide variations in spectral content. Results provide clear guidance for design of future large scale community surveys, where one must optimize the complex tradeoffs between the size of the surveyed population, spatial footprint of those participants, and the fidelity/density of objective measurements. [ABSTRACT FROM AUTHOR]

An evaluation of noise metrics for predicting human perception of sonic booms was performed. Twenty-five metrics were chosen from standards and from the literature in an effort to include all potentially relevant metrics. Three different datasets of sonic boom waveforms and associated human response were chosen to span a variety of signals, including traditional N-waves with various shock shapes and rise times, and predicted waveforms from designs of low-boom aircraft for a variety of aircraft sizes. These datasets were derived from laboratory studies conducted in sonic boom simulators at NASA Langley Research Center and JAXA. Simulations of booms experienced in both outdoor and indoor environments were included by using different facilities at NASA or modifications to facility configurations at JAXA. American and Japanese test subjects participated at NASA and JAXA, respectively. Ratings of loudness using a magnitude estimation technique and ratings of annoyance using a category line scaling method are included. The evaluation consists of linear correlations of human response data with the objective noise metrics. Results are presented for each study, and eight metrics are suggested for further analysis. [ABSTRACT FROM AUTHOR]

Sonic boom is one of the key issues to be considered in the development of future supersonic or hypersonic civil aircraft concepts. The classical sonic boom, typical for Concorde with an N-wave shape and a ground amplitude of the order of 100 Pa, prevents overland flight. Future concepts target carefully shaped sonic booms with low amplitude weak shocks. However, sonic boom when perceived at the ground level is influenced not only by the aircraft characteristics, but also by atmospheric propagation. In particular, the effect of atmospheric turbulence on sonic boom propagation near the ground is not well characterized. Flight tests performed as early as the 1960s demonstrated that classical sonic booms are sensitive to atmospheric turbulence. However, this sensitivity remains only partially understood. This is related to the fact that i) turbulence is a random process that requires a statistical approach, ii) standard methods used to predict sonic booms, mainly geometrical acoustics based on ray tracing, are inadequate within the turbulent planetary boundary layer. Moreover, the ray theory fails to predict the acoustical field in many areas of interest, such as caustics or shadow zones. These zones are of major interest for sonic boom acceptability (highest levels, lateral extent of zone of impact). These limitations outline the need for a numerical approach that is sufficiently efficient to perform a large number of realizations for a statistical approach, but that goes beyond the limitations of ray theory. With this in view, a 3D one-way numerical method solving a nonlinear scalar wave equation established for heterogeneous, moving and absorbing atmosphere, is used to assess the effects of a 3D kinematic turbulence on sonic boom in various configurations. First, a plane N-wave is propagated in the free field through random realizations of kinematic fluctuations. Then the case of a more realistic Atmospheric Boundary Layer (ABL) is investigated, with a mean stratified wind superimposed to a 3D random turbulent realization. Propagation is performed either in the case of a shadow zone or of an atmospheric waveguide. To model the turbulent ABL, the mean flow and the fluctuations are handled separately. The wind fluctuations are generated using the Random Fluctuations Generation method assuming a von K'arm'an spectrum and a homogeneous and isotropic turbulence. The mean stratified wind is modeled based on the Monin-Obhukov Similarity Theory (MOST). To illustrate the method, the typical case of a sunny day with a strong wind has been chosen. Statistics are obtained on several parameters. It shows the importance of turbulence, which leads to an increase of the mean maximum peak pressure in the shadow zone and to its decrease in the waveguide. Moreover, the formation of random caustics that can lead to an increase of the noise perceived locally is outlined. [ABSTRACT FROM AUTHOR]

In support of the ongoing effort by the National Aeronautics and Space Administration (NASA) to bring supersonic commercial travel to the public, NASA, in partnership with other industry organizations, conducted a flight research experiment to analyze acoustic propagation at the lateral edge of the sonic boom carpet. The name of the effort was the Farfield Investigation of No-boom Thresholds (FaINT). The research from FaINT determined an appropriate metric for sonic boom waveforms in the transition and shadow zones called Perceived Sound Exposure Level, established a value of 65 dB as a limit for the acoustic lateral extent of a sonic boom's noise region, analyzed change in sonic boom levels near lateral cutoff, and compared between real sonic boom measurements and numerical predictions. [ABSTRACT FROM AUTHOR]

Shown in this paper is an introduction of a prediction tool for the propagation of loud noise with the application to the aeronautics in mind. The tool, named SPnoise, is based on HOWARD approach, which can express almost exact multidimensionality of the diffraction effect at the cost of back scattering. This paper argues, in particular, the prediction of the effect of atmospheric turbulence on sonic boom as one of the important issues in aeronautics. Thanks to the simple and efficient modeling of the atmospheric turbulence, SPnoise successfully re-creates the feature of the effect, which often emerges in the region just behind the front and rear shock waves in the sonic boom signature. [ABSTRACT FROM AUTHOR]

Sources of aerial shock waves are numerous and produce acoustical signals that propagate in the atmosphere over long ranges, with a wide frequency spectrum ranging from infrasonic to audible, and with a complex human response. They can be of natural origin, like meteors, lightning or volcanoes, or human-made as for explosions, so-called "buzz-saw noise" (BSN) from aircraft engines or sonic booms. Their description, modeling and data analysis within the viewpoint of nonlinear acoustics will be the topic of the present lecture, with focus on two main points: the challenges of the source description, and the main features of nonlinear atmospheric propagation. Inter-disciplinary aspects, with links to atmospheric and geo-sciences will be outlined. Detailed description of the source is very dependent on its nature. Mobile supersonic sources can be rotating (fan blades of aircraft engines) or in translation (meteors, sonic boom). Mach numbers range from transonic to hypersonic. Detailed knowledge of geometry is critical for the processes of boom minimization and audible frequency spectrum of BSN. Sources of geophysical nature are poorly known, and various mechanisms for explaining infrasound recorded from meteors or thunderstorms have been proposed. Comparison between recorded data and modeling may be one way to discriminate between them. Moreover, the nearfield of these sources is frequently beyond the limits of acoustical approximation, or too complex for simple modeling. A proper numerical description hence requires specific matching procedures between nearfield behavior and farfield propagation. Nonlinear propagation in the atmosphere is dominated by temperature and wind stratification. Ray theory is an efficient way to analyze observations, but is invalid in various situations. Nonlinear effects are enhanced locally at caustics, or in case of grazing propagation over a rigid surface. Absorption, which controls mostly the high frequency part of the spectrum contained within shocks, is controlled by humidity, cloudiness or surface properties. Variability is large at all scales, and depends simultaneously on climate, daily meteorology, and local turbulent state, especially near the ground in the planetary boundary layer. Numerous features of outdoor propagation remain to be explored in the nonlinear case, such as complex 3D atmospheric description (role of turbulence, partial reflections, gravity waves) or topography. [ABSTRACT FROM AUTHOR]

This paper presents a time domain formulation of nonlinear lossy propagation in onedimension that also includes the effects of non-collinear mean flow in the acoustic medium. The model equation utilized is an augmented Burgers equation that includes the effects of nonlinearity, geometric spreading, atmospheric stratification, and also absorption and dispersion due to thermoviscous and molecular relaxation effects. All elements of the propagation are implemented in the time domain and the effects of non-collinear mean flow are accounted for in each term of the model equation. Previous authors have presented methods limited to showing the effects of wind on ray tracing and/or using an effective speed of sound in their model equation. The present work includes the effects of mean flow for all terms included in the augmented Burgers equation with all of the calculations performed in the time-domain. The capability to include the effects of mean flow in the acoustic medium allows one to make predictions more representative of real-world atmospheric conditions. Examples are presented for nonlinear propagation of N-waves and shaped sonic booms. [Work supported by Gulfstream Aerospace Corporation.] [ABSTRACT FROM AUTHOR]

Global variation of sonic boom overpressures with the realistic atmospheric gradients was discussed. The atmospheric gradients were estimated by upper-air observational radiosonde data and a simple N-wave was extrapolated through all seasonal atmospheric gradients without winds around the world. Results demonstrated that sonic boom overpressure varies widely with season and geographic position compared to that of the standard atmospheric condition. The results also showed the tendencies of the global variation in overpressure. [ABSTRACT FROM AUTHOR]

Noise annoyance due to sonic boom is one of the serious problems for development of next-generation supersonic transport. To decrease this sonic boom noise, the design and analysis techniques are developed at Japan Aerospace eXploration Agency (JAXA). To predict the sonic boom on the ground accurately, we have developed a numerical code (Xnoise) using the augmented Burgers equation combined with the ray tracing. In this method, effects of nonlinearity, geometrical spreading, inhomogeneity of atmosphere, thermoviscous attenuation, molecular vibration relaxation and winds are taken into account. This method gives an estimation of the rise times of ground signatures without resorting to the weak shock theory and area balancing techniques. The nonlinear term is evaluated by the finite difference scheme in this method. In ray-path calculation, an explicit updating methodology is adopted. The augmented Burgers equation is numerically solved by using the operator split method entirely in the time domain. As for the effects of nonlinearity, geometrical spreading, and atmospheric inhomogeneity, the result obtained with the augmented Burgers equation agrees well with that obtained with the waveform parameter method (Thomas' method). For the effects of absorption and dispersion, the calculation based on the augmented Burgers equation is verified by comparing with a detailed one-dimensional CFD analysis. Moreover, we show calculations which account the effect of winds on the propagation of a sonic boom. The validation of model is a future work. [ABSTRACT FROM AUTHOR]

Acoustical shock waves propagate through flows in many situations. The sonic boom produced by a supersonic aircraft influenced by winds, or the so-called Buzz-Saw-Noise produced by turbo-engine fan blades when rotating at supersonic speeds, are two examples of such a phenomenon. In this work, an original method called FLHOWARD, acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction, is presented. It relies on a scalar nonlinear wave equation, which takes into account propagation in a privileged direction (one-way approach), with diffraction, flow, heterogeneous and nonlinear effects. Theoretical comparison of the dispersion relations between that equation and parabolic equations (standard or wide angle) shows that this approach is more precise than the parabolic approach because there are no restrictions about the angle of propagation. A numerical procedure based on the standard split-step technique is used. It consists in splitting the nonlinear wave equation into simpler equations. Each of these equations is solved thanks to an analytical solution when it is possible, and a finite differences scheme in other cases. The advancement along the propagation direction is done with an implicit scheme. The validity of that numerical procedure is assessed by comparisons with analytical solutions of the Lilley's equation in waveguides for uniform or shear flows in linear regime. Attention is paid to the advantages and drawbacks of that method. Finally, the numerical code is used to simulate the propagation of sonic boom through a piece of atmosphere with flows and heterogeneities. The effects of the various parameters are analysed. [ABSTRACT FROM AUTHOR]

Dassault Aviation as a civil aircraft manufacturer is studying the feasibility of a supersonic business jet with the target of an “acceptable” sonic boom at the ground level, and in particular in case of focusing. A sonic boom computational process has been performed, that takes into account meteorological effects and aircraft manoeuvres. Turn manoeuvres and aircraft acceleration create zones of convergence of rays (caustics) which are the place of sound amplification. Therefore two elements have to be evaluated: firstly the geometrical position of the caustics, and secondly the noise level in the neighbourhood of the caustics. The modelling of the sonic boom propagation is based essentially on the assumptions of geometrical acoustics. Ray tracing is obtained according to Fermat's principle as paths that minimise the propagation time between the source (the aircraft) and the receiver. Wave amplitude and time waveform result from the solution of the inviscid Burgers' equation written along each individual ray. The “age variable” measuring the cumulative nonlinear effects is linked to the ray tube area. Caustics are located as the place where the ray tube area vanishes. Since geometrical acoustics does not take into account diffraction effects, it breaks down in the neighbourhood of caustics where it would predict unphysical infinite pressure amplitude. The aim of this study is to describe an original method for computing the focused noise level. The approach involves three main steps that can be summarised as follows. The propagation equation is solved by a forward marching procedure split into three successive steps: linear propagation in a homogeneous medium, linear perturbation due to the weak heterogeneity of the medium, and non-linear effects. The first step is solved using an “exact” angular spectrum algorithm. Parabolic approximation is applied only for the weak perturbation due to the heterogeneities. Finally, non linear effects are performed by solving the in-viscid Burgers' equation. As this one is valid for a plane wave, the direction of this last one is not prescribed a priori, but is computed in a self-adaptative way using an efficient numerical solver of the non-linear eikonal equation (Fast Marching Method). [ABSTRACT FROM AUTHOR]

The purpose of this presentation is to briefly outline the progress and achievements that have occurred in some areas of nonlinear acoustics during recent years. [ABSTRACT FROM AUTHOR]

Analyses of acoustic data recorded during a series of high thrust military jet flyovers indicate that the skewness of the pressure is not well correlated with the sound pressure level, but the skewness of the gradient is. The influence of propagation distance and engine exhaust velocity on the results requires further examination. The results presented here emphasize the need for high bandwidth, high signal to noise ratio measurements. [Work supported by the Strategic Environmental Research and Development Program.] © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Dassault Aviation as a civil aircraft manufacturer is studying the feasibility of a supersonic business jet. One of the prerequisites for an environmentally friendly and economically viable supersonic aircraft is that its sonic boom signature is reduced to a level acceptable for flight over populated areas. The method presented here is part of the Dassault Aviation toolbox dedicated to the evaluation and/or to the design process of a low boom constrained supersonic aircraft. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The shock waves generated by a supersonic aircraft are reflected in the upper part of the atmosphere. Back to the ground, they are indirect sonic booms called secondary sonic booms. The recorded signals of secondary sonic booms show a low amplitude and a low frequency. They sound like rumbling noises due to amplitude bursts. These signals strongly depend on the atmospheric conditions, in particular to the amplitude and to the direction of the wind in the stratopause. In the present work, the propagation of secondary sonic booms is studied using realistic atmospheric models up to the thermosphere. The secondary carpet position is investigated by solving temporal ray equations. An amplitude equation including nonlinearity, absorption and relaxation by various chemical species is coupled to the ray solver to get the secondary boom signature at the ground level. Multipath arrivals are directly linked to wind field or 3D inhomogeneities. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The influence of the meteorological variability on the characteristics of the sonic-boom from a projected commercial SST aircraft is investigated. The sonic boom is calculated by means of an advanced algorithm, taking into account nonlinear distortion, absorption, refraction including shadow zones, and focusing effects. Real meteorological situations are considered based on a full ten-year data set in 12 and/or 24 hour resolution. Three different climate regions are studied: a mid-latitude coastal sea region, a tropical coastal sea area, and a sub-polar land region. For the acceleration phase, the study is limited to a one year data set above the English Channel for flights from Paris to New York. Frequency distributions of sonic boom characteristics such as wave amplitude, rise time, carpet width, location, strength and geometrical extension of caustics are shown for each area, all seasons and opposing flight directions. While variability turns out to be low for cruising-flight boom at the ground track, it is high laterally and for focused boom (carpet width or caustic length, waveboom amplitude). © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

It is challenging to develop a physics-based model for propagation through atmospheric turbulence. A number of models are currently available but are typically not based on experimental results. A fresh approach might be to construct some type of “black box” filter function for producing typical distorted sonic boom waveforms on the ground. The input to the filter could be arbitrary, non-distorted sonic boom waveforms above the turbulence. As an initial model, a single input-output system was assumed. Ground-recorded waveforms were used as outputs of the system. The transfer function between the two signals was estimated using Welch’s average periodogram method. Data obtained from the 2004 Shaped Sonic Boom Experiment (SSBE) was analyzed and corresponding transfer functions were obtained. With such transfer functions established, FIR filters were determined and convolved with an appropriate input waveform. Such FIR filters allow for the production of “typical” atmospherically distorted waveforms given arbitrary input waveforms. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A closed tank of dimensions 0.5 × 0.5 × 2.7 m3, filled with a mixture of ethanol and water to produce an almost linear sound speed profile with a gradient near 450 (m/s)/m, served the purpose for investigating shocked sound wave propagation in a stratified environment. As the sound speed profile evolved by diffusion a number of different measurements were taken, both in areas with caustics, shadow zones, along the main beam and along the bottom. After about one year, part of the fluid was re-mixed to obtain a pronounced sound speed maximum some 20 cm above the bottom. The high intensity sound was produced by a plane circular piston type sound source with near-field length 45 cm and half power angle 0.8° at 1.1 MHz, placed near one end of the tank. Its tilt angle and depth could be varied. A 0.5 mm diameter PVDF needle hydrophone (Precision Acoustics) mapped the sound field in a vertical slice in the range 0.9 – 2.4 m, remotely controlled by a PC. We present results from measurements in a shadow zone and along the bottom. The latter, in particular, displays unexpected amplitude variations. The project was funded by the European Commission, contract number G4RD-CT-2000-00398. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The target sonic boom shock strength specified in the DARPA Quiet Supersonic Platform project was 0.3 psf. The potential acceptability of that overpressure is based to a large degree on the expected relaxation-driven shock structure. It has previously been difficult to obtain sonic booms in that range from aircraft, so there had been no flight test data verifying the shock structure of such minimized booms. Low amplitudes do occur, but they are generally near the edge of the boom carpet, are distorted by ground effects, and do not represent the kind of primary boom that is expected from a low-boom aircraft. Recent flights of sounding rockets have generated low overpressure booms, providing an opportunity to examine weak boom shock structures as they occur under real atmospheric propagation. One extraordinarily clean 0.2 psf N-wave provided a shock structure which is quantitatively compared with relaxation theory. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The sonic boom at a large distance from its source consists of a leading shock, a trailing shock and a one parameter family of nonlinear wavefronts in between these shocks. A new ray theoretical method using a shock ray theory and a weakly nonlinear lay theory has been used to obtain the shock fronts and wavefronts respectively, for a maneuvering aerofoil in a homogeneous medium. This method introduces a one parameter family of Cauchy problems to calculate the shock and wave fronts emerging from the surface of the aerofoil. These problems are solved numerically to obtain the leading shock front and the nonlinear wavefronts emerging from the front portion of the aerofoil. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The sonic-boom focusing problem has been solved using the nonlinear Tricomi equation. A pseudo time term has been added to the equation so that marching in pseudo time will be possible. The solution is obtained by splitting the nonlinear unsteady equation into two parts: a part corresponding to a linear unsteady Tricomi equation, and another part corresponding to an unsteady nonlinear Burgers equation. The solution of the linear unsteady Tricomi equation is followed by the solution of the nonlinear unsteady Burgers equation to obtain the solution of the total nonlinear equation. The solution of the linear unsteady Tricomi equation has been accomplished using two schemes. The first is a frequency-domain (FD) spectral scheme and the second is a time-domain (TD) finite-differencing scheme. The solution of the nonlinear unsteady Burgers equation has also been accomplished using two schemes. The first is a finite-difference scheme and the second is an analytical scheme. Thus, there are four combinations to obtain the solution of the nonlinear Tricomi equation. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The recent flight demonstration of shaped sonic booms shows the potential for quiet overland supersonic flight, which could revolutionize air transport. To successfully design quiet supersonic aircraft, the upper limit of an acceptable noise level must be determined through quantitative recording and subjective human response measurements. Past efforts have concentrated on the use of sonic boom simulators to assess human response, but simulators often cannot reproduce a realistic sonic boom sound. Until now, molecular relaxation effects on low overpressure rise time had never been compared with flight data. Supersonic flight slower than the cutoff Mach number, which generates evanescent waves, also prevents loud sonic booms from impacting the ground. The loudness of these evanescent waves can be computed, but flight measurement validation is needed. A novel flight demonstration technique that generates low overpressure N-waves using conventional military aircraft is outlined, in addition to initial quantitative flight data. As part of this demonstration, evanescent waves also will be recorded. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Lessons learned from the 1960’s sonic boom tests at St. Louis, Oklahoma City and at Edwards Air Force Base (EAFB) and more recently in communities near EAFB and Nellis AFB are briefly reviewed from the standpoint of building vibration and rattle response induced by the sonic boom signature. Available data on the vibro-acoustic threshold of rattle are considered along with the principal sonic boom signature parameters, peak overpressure and duration, which drive the low frequency vibration response of buildings to sonic booms. Implications for the current effort to develop an acceptable sonic boom signature are considered with this overview of current understanding of building vibration response to sonic booms. Possible gaps in this current knowledge for current technology boom signatures are considered. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Atmospheric absorption may have a huge impact on the sonic boom annoyance by reducing the amplitude and increasing the rise time. However, the standard absorption due to the vibrational relaxation of molecular nitrogen and oxygen does not estimate the influence of clouds where scattering by water droplets occurs. As clouds cover more than 50 % of the Earth surface, their influence on sonic boom needs estimation. Test flights performed in the former Sowiet Union in 1967–1968 indicate a strong impact. An existing model for acoustical propagation in a polydispersed air-vapor-droplet suspension is reviewed. It takes into account energy and viscous momentum transfer as well as evaporation processes influenced by diffusion of vapor through the air. When applied to the conditions prevailing in atmospherical clouds, it shows a dramatical increase of sound attenuation and dispersion. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The recent Shaped Sonic Boom Experiment yielded a large number of digital recordings of shaped and N-wave sonic boom waveforms, all of which exhibited some degree of turbulent distortion. This digital data set provided an opportunity to test theoretical predictions of the shape of distortions, and to assess the effect of turbulence on the loudness of shaped booms. Distortions following the shocks were found to be virtually identical for the bow and tail shocks of each boom, confirming the usual explanation that the distortion is scattering of the shock waves and that turbulence may be considered to be frozen for the duration of a boom. RMS values of the distortions have been compared with the theory of S. C. Crow. The loudness reduction of shaped booms had been predicted by Plotkin to persist through turbulence, and this was found to be the case. The loudness calculations also confirmed that the benefit of reduced shock amplitude is nonlinear: there are benefits from both the reduced amplitude and from the increased shock thickness. (A full version of this paper was presented at the 2005 AIAA/CEAS Aeroacoustics Conference as AIAA-2005-2949.) © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The influence of the planetary boundary layer on the sonic boom received at the ground level is known since the 60s to be a major importance, with a decrease of the mean pressure, an increase of the mean rise time but a huge variability. A generalized “KZ” paraxial approximation of the nonlinear wave equation is obtained in a weakly heterogeneous (small temperature fluctuations) and slowly moving medium (small Mach number), two consistent approximations for the atmosphere. For a non-moving medium, the generalized KZ equation is solved numerically using a finite differences scheme adapted from one developed for sonic boom focusing. To validate quantitatively the model in a deterministic way, experiments are conducted at a 1:100 000 scale for ultrasonic shocks in a water tank. Atmospheric heterogeneities are simulated by introducing cylindrical (sub)wavelength silicon tubes. Experiments and simulation of the nonlinear pressure fields are in very good agreements. The sensitivity of the scattered signal to the size of the heterogeneities is investigated. Also the influence of nonlinear effects on the shock wave/heterogeneity interaction is examined. Finally, the limitation of the paraxial approximation for wave scattering are discussed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A number of physical processes work to modify the shape of sonic boom waveforms as the waveform propagates from the aircraft to a receiver on the ground. These include frequency-dependent absorption, nonlinear steepening, and scattering by atmospheric turbulence. In the past two decades, each of these effects has been introduced into numerical prediction algorithms and results compared to experimental measurements. There is still some disagreement between measurements and prediction, but those differences are now in the range of tens of percent. The processes seem to be fairly well understood and the present understanding of sonic boom evolution will be presented. An area of possible future development is the marrying of this propagation understanding with advances made in computational fluid dynamics (CFD) and scale model jet tests to predict the near field sonic boom waveform from aircraft shape and flight characteristics. Such a capability would allow for complete modeling from aircraft to ground impact and as such would represent a significant design tool to effectively evaluate proposed aircraft designs for reduced sonic boom impact. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Presented paper is a brief overview of current efforts in sonic boom area taking place in the Russian Central Aerohydrodynamic Institute in cooperation with the Flight Research Institute. These efforts are focused on improvement of existing methods and development of new ones, minimization technique development, study of sonic boom atmospheric effect, search of low boom aircraft configurations in different weight categories, having good aerodynamic characteristics. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Over the past 15 years, NASA Langley Research Center has conducted many tests investigating subjective response to simulated sonic booms. Most tests have used the Sonic Boom Booth, an airtight concrete booth fitted with loudspeakers that play synthesized sonic booms pre-processed to compensate for the response of the booth/loudspeaker system. Tests using the Booth have included investigations of shaped booms, booms with simulated ground reflections, recorded booms, outdoor and indoor booms, booms with differing loudness for bow and tail shocks, and comparisons of aircraft flyover recordings with sonic booms. Another study used loudspeakers placed inside people’s houses, so that they could experience the booms while in their own homes. This study investigated the reactions of people to different numbers of booms heard within a 24-hour period. The most recent Booth test used predicted boom shapes from candidate low-boom aircraft. At present, a test to compare the Booth with boom simulators constructed by Gulfstream Aerospace Corporation and Lockheed Martin Aeronautics Company is underway. The Lockheed simulator is an airtight booth similar to the Langley booth; the Gulfstream booth uses a traveling wave method to create the booms. Comparison of “realism” as well as loudness and other descriptors is to be studied. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A method is presented to simulate sonic booms using high fidelity and custom-built audio equipment that output to an acoustically treated listening environment, all of which is contained in a portable vehicle. The audio system has inherent low and high frequency performance limitations and also introduces distortion due to the frequency response of the system. The limitations of the system are compensated for by band-pass filtering a full-fidelity sonic boom signature and applying a system equalization filter. The purpose of the band-pass filter is to remove frequency content above and below the capabilities of the system yet retain the audible and felt characteristics of the full-fidelity waveform. The equalization filter, computed from time-domain Wiener filtering, compensates for the frequency-dependent system response of the audio system at several listening positions. The system performance is evaluated by comparing the PLdB, SEL(A) and SEL(C) of the measured system output to the full-fidelity waveform. Results show good agreement between the loudness levels of the full-fidelity waveform and the corresponding measured system output. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

As part of a French research program, a sound restitution cabin was designed for investigating the annoyance of sonic boom signals. The first goal was to reproduce the boom spectrum and temporal waveform: this required linear generation of high pressure levels at infrasonic frequencies (110 SPL dB around 3 Hz), and response equalization over the full frequency range (1 Hz–20 kHz). At this stage the pressure inside the cabin was almost uniform around the listener, emulating an outdoor situation. A psychoacoustic study was then conducted which confirmed that the loudness (related to annoyance) of N-waves is roughly governed by the peak pressure, the rise/fall time, and the wave duration. A longer-term goal is to reproduce other aspects of an indoor situation including rattle noise, ground vibrations, and a more realistic spatial repartition of pressure. This latter point has been addressed through an Active Noise Control study aiming at monitoring the low-frequency acoustic pressure on a surface enclosing a listener. Frequency and time-domain numerical simulations of boom reproduction via ANC are given, including a sensitivity study of the coupling between a listener’s head and the incident boom wave which combine into the effective sound-field to be reproduced. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]