Search

When it comes to publishing research results in a thesis or journal article, a disconnect between advisor expectations and student abilities can be a source of frustration, fear, and deteriorated relationships. Publishing in conference publications, including Proceedings of Meetings on Acoustics (POMA), represents an opportunity to bridge this gap. This paper describes several benefits of publishing in conference proceedings, how to use POMA as a springboard to further publication, and some suggestions to help students and advisors overcome publication barriers.

This paper summarizes a two-part session, “Supersonic Jet Aeroacoustics,” that took place during the 176th Meeting of the Acoustical Society of America. The sessions were cosponsored by the Noise and Physical Acoustics Technical Committees and consisted of talks by government, academic, and industry researchers from institutions in the United States, Canada, Japan, South Korea, and India. The sessions described analytical, computational, and experimental approaches to both fundamental and applied problems on model and full-scale jets and rocket exhaust plumes.

Crackle is an annoying perceptual component of supersonic jet noise. In the far field, crackle is related to the presence of acoustic shocks that develop due to nonlinear propagation, however, the intermittent source events that drive crackle generation are not well understood. This study investigates the apparent source locations of events related to crackle, which include high-amplitude or steepened, shock-like waveforms. The measured data were obtained through ground-array measurements near a high-performance military aircraft. The apparent source regions corresponding radiation angle, the skewness of the time-derivative of the pressure waveform (dSk), and overall sound pressure level are defined. Waveforms consisting of a dSk greater than 3 are considered to contain crackle. For 75% engine thrust request, the apparent source region for the top 1000 derivative events beamformed from locations with high derivative skewness, which corresponds to the potential for crackle, is 2-7 m downstream of the nozzle along the jet axis.

Recent demonstrations of real-time source localization systems have used a variety of direction-finding methods. One such system uses a multi-microphone probe to estimate acoustic intensity [Inoue et al., Proc. Meetings Acoust. 29, 025001 (2016)], although the bandwidth of intensity estimates are traditionally limited by the microphone spacing. The Phase and Amplitude Gradient Estimator (PAGE) method [Thomas et al., J. Acoust. Soc. Am. 137, 3366–3376 (2015)] greatly extends the bandwidth of active intensity, providing an accurate method of source localization for a wide bandwidth. An initial system implemented in LabVIEW estimates active intensity using the PAGE method to identify the direction of the source location in real time. Using a paired webcam, the program then overlays the direction as a three-dimensional arrow onto a webcam image. An experiment in an anechoic chamber shows the accuracy of the system is approximately five degrees within the camera’s field of view and the application of real-time drone tracking is also discussed.

Characterization of far-field jet noise spectral evolution can be performed locally with a single microphone measurement using a gain factor that stems from the ensemble-averaged, frequency-domain version of the generalized Burgers equation. The factor quantifies the nonlinear change in the sound pressure level spectrum over distance [B. O. Reichman et al., J. Acoust. Soc. Am. 139, 2505-2513 (2016)]. Here, noise waveforms from a high-performance military jet aircraft are characterized with this gain factor and compared to propagation losses from geometric spreading and atmospheric absorption. Far-field results show that the high-frequency nonlinear gains at high frequencies tend to balance the absorption losses, thus establishing the characteristic spectral slope present in shock-containing noise. Differences as a function of angle, distance, and engine condition are explored.

Crackle is a perceptual aspect of noise caused by impulsive acoustic shocks and observed in noise from supersonic jets, including those from military aircraft and rockets. Overall and long-term spectral noise metrics do not account for the unique perception of crackle. Listening tests were designed to better understand perception of crackle and examine its relationship to physical noise metrics, such as skewness of the first time derivative of the pressure waveform, hereafter derivative skewness. It is hypothesized that as derivative skewness increases, the perception of crackle tends to increase. Two listening tests were conducted with 31 subjects to examine their perception of crackle. In the first test, subjects compared and ordered crackle-containing sounds. In the second test, category scaling was employed with subjects rating the crackle content with category labels: 1) smooth noise with no crackle, 2) rough noise with no crackle, 3) sporadic or intermittent crackle, 4) continuous crackle, and 5) intense crackle. Both the order and rating tests confirm there is a high correlation between perception of crackle and derivative skewness. These insights will help inform community noise models, allowing them to incorporate annoyance due to jet crackle.

Vacuum-assisted toilet noise can be unsettling and even uncomfortable. One common way to reduce noise levels is to damp structural vibrations that radiate sound. Constrained layer damping (CLD) treatments were investigated for their effectiveness to reduce the radiated noise level on a vacuum-assisted toilet. To find the modal response of the toilet bowl, a commercial vacuum-assisted toilet was excited with a shaker and measured the velocity response of the inside of the bowl with a 3-dimensional scanning laser Doppler. The bowl was also scanned with an accelerometer during a repeated flush cycle. A microphone placed one meter above the bowl measured the radiated sound level. 3M 4014, Pyrotek Decidamp CLD, and Velcro were each applied to the bowl to determine the reduction in structural vibrations and sound radiation. The front-half of the bowl’s rim had the largest velocity amplitude. Structural vibrational energy concentrated around 100-500 Hz while radiated sound concentrated around 300 Hz–2 kHz. Applying damping materials reduced structural vibrations, sometimes by 20 dB. Lightweight treatments certainly can reduce structural vibrations.

Multisource statistically optimized near-field acoustical holography (M-SONAH) improves the field reconstruction process by directly incorporating into the pressure propagator types of wavefunctions that correspond most closely to the source geometries of interest [A. T. Wall et al., J. Acoust. Soc. Am. 137, 963–975 (2015)]. The M-SONAH method has previously been used to localize acoustic sources in a full-scale jet engine plume above a rigid reflecting plane by adding a second set of cylindrical wavefunctions corresponding to the image source [A. T. Wall et al. J. Acoust. Soc. Am. 139, 1938–1950 (2016)]. Here, M-SONAH theory is extended to obtain the vector particle velocity and, by extension, the acoustic intensity. Discussed are two examples that relate to the full-scale jet noise-with-image-plane reconstruction problem: (1) a Gaussian line source with image and (2) a jet-like wavepacket and image, with hologram geometry identical to that of the full-scale experiment. The results from both examples rev...

A frequency-domain representation of the Burgers equation reveals that the cross-spectrum between the pressure and pressure-squared waveforms can be used to calculate nonlinear frequency-domain effects of finite-amplitude sound propagation. The normalized version of the quadspectrum, Q/S, was introduced by Morfey and Howell and has since been used to point to the nonlinear transfer of energy between frequencies, in particular gaining use in the domain of high-amplitude jet noise propagation. However, one question that remained was that of the interpretation: The physical meaning of the amplitude of Q/S was unclear. Recent analytical work has recast Q/S and the normalized version of the cospectrum, C/S, as a way to estimate sound pressure level and phase changes due to nonlinearity with a single-point measurement. This paper uses various measurements within a plane-wave tube to verify the physical significance of the amplitude and phase changes predicted by Q/S and C/S. Experiments involving sinusoids and band-passed Gaussian noise at various amplitudes show the validity of the single-point measurement to measure the strength of nonlinear effects in both amplitude and phase.

Crackling signals cannot be identified using any sound level or quality metric that relies solely on the long-term spectrum as input. In order to identify sound quality metrics that might succeed in modeling human perception of crackling and non-crackling sounds a set of metrics sensitive to temporal properties of signals is applied to a set of signals with equivalent spectra but exhibiting varying degrees of crackle. Several methods for altering signals including some that remove crackling sound quality from an acoustic signal were drawn from previous work [Swift, Gee, Neilsen, 2014, Swift, Gee, Neilsen, 2017]. In this paper, an additional alteration which can partially remove crackle—randomizing the Fourier phase of a crackling signal in the frequency domain in selected frequency ranges—is considered. Variables from time-varying sound quality metrics such as loudness and sharpness, as well as roughness to signals exhibiting varying degrees of crackle are explored and relationships between them that can ...

The phase and amplitude gradient estimator (PAGE) method [D.C. Thomas et al., J. Acoust. Soc. Am. 137, 3366-3376 (2015)] has proven successful in improving the accuracy of measured energy quantities over the traditional p-p method in several applications. One advantage of the PAGE method is the use of phase unwrapping, which can provide increased measurement bandwidth. However, narrowband sources often do not have coherent phase information over a sufficient bandwidth for a phase unwrapping algorithm to unwrap properly. Still, the PAGE method yields correct acoustic intensity measurements for frequencies up to the spatial Nyquist frequency for both broadband and narrowband sources. This is an improved bandwidth over the traditional method. For narrowband sources above the spatial Nyquist frequency, special conditions or processing are necessary for the PAGE method to provide accurate acoustic intensity. With sufficient bandwidth and a coherence of at least 0.1 at the spatial Nyquist frequency, a relatively narrowband source above the spatial Nyquist frequency can be unwrapped accurately. Also, with an assumption of a propagating field, and therefore linear phase, the extrapolated PAGE method uses the phase of a tone below the spatial Nyquist frequency to extrapolate phase above the spatial Nyquist frequency.The phase and amplitude gradient estimator (PAGE) method [D.C. Thomas et al., J. Acoust. Soc. Am. 137, 3366-3376 (2015)] has proven successful in improving the accuracy of measured energy quantities over the traditional p-p method in several applications. One advantage of the PAGE method is the use of phase unwrapping, which can provide increased measurement bandwidth. However, narrowband sources often do not have coherent phase information over a sufficient bandwidth for a phase unwrapping algorithm to unwrap properly. Still, the PAGE method yields correct acoustic intensity measurements for frequencies up to the spatial Nyquist frequency for both broadband and narrowband sources. This is an improved bandwidth over the traditional method. For narrowband sources above the spatial Nyquist frequency, special conditions or processing are necessary for the PAGE method to provide accurate acoustic intensity. With sufficient bandwidth and a coherence of at least 0.1 at the spatial Nyquist frequency, a relativel...

The phase and amplitude gradient estimator (PAGE) method can be used to increase the bandwidth of complex acoustic intensity estimates obtained with multi-microphone probes. Despite the increased bandwidth, errors arise when using this method, which is based on linear least-squares gradients, in non-planar fields. Examples of non-planar fields include the acoustic near field of a radiating source or near a null in a standing-wave field. The PAGE method can be improved by increasing the number of microphones and using a Taylor expansion to obtain higher-order estimates of center pressure, pressure amplitude gradient, and phase gradient. For one-dimensional active intensity in a simulated monopole field, a four-microphone probe is shown to converge to less than 0.2 dB error at a closer distance than a two-microphone probe with the same inter-microphone spacing. For reactive intensity in a standing wave field, increasing the number of microphones improves the bandwidth, and applying a higher-order method to ...

This paper summarizes a two-part special session, “Supersonic Jet and Rocket Noise,” which was held during the 174th Meeting of the Acoustical Society of America in New Orleans, Louisiana. The sessions were cosponsored by the Noise and Physical Acoustics Technical Committees and consisted of talks by government, academic, and industry researchers from institutions in the United States, Japan, France, and India. The sessions described analytical, computational, and experimental approaches to both fundamental and applied problems on model and full-scale jets and rocket exhaust plumes.

A coherence-based method for unwrapping the relative phase between microphones is investigated. For broadband signals, this method has the potential to lead to more accurate intensity vector estimations using the Phase Amplitude and Gradient Estimator (PAGE) method [D. C. Thomas et al., J. Acoust. Soc. Am. 137, 3366-3376 (2015)] Simple unwrapping methods function by detecting phase jumps above a threshold value, which works well for frequencies associated with high signal coherence. However, since unwrapping for these methods is triggered by only one previous frequency data point, frequency ranges of low coherence often contain unwrapping errors. By including coherence in a phase unwrapping algorithm, these errors can be avoided. Ranges of relatively low coherence are given less weight in phase unwrapping and are checked for unwrapping errors. For broadband signals with continuous relative phase, using both the coherence and multiple data points to unwrap, frequencies associated with low coherence result ...

In an advanced acoustics laboratory course at Brigham Young University, students are introduced to ANSI measurement standards in the context of sound power. They are introduced to the anatomy of a typical acoustics standard and then plan and carry out sound power measurements of an electric leaf blower using both reverberation chamber and sound intensity methods. The students are required to write a technical memorandum describing a) the blower’s radiated sound power levels over an appropriate frequency range, as obtained with the two methods; b) setup documentation and deviations from the standards’ recommended practices; and c) how any deviations might have contributed to discrepancies between the sound power levels obtained with the two methods. In this paper, a description of the experience is given, along with overall impressions and plans for future improvements.

The apparent acoustic source region of jet noise varies as a function of frequency. In this study, the variation of the apparent maximum source location with frequency is considered for an ideally expanded, unheated, Mach-1.8 jet with exit diameter of 20 mm. In this study, the source location is ascertained for one-third octave bands by evaluating peak cross-correlation between near-field linear microphone arrays at three sideline distances and a far-field microphone arc. The impact of the hydrodynamic field on correlation results is considered. Source locations determined by these means are compared with intensity analyses for the same jet [K. L. Gee et al., AIAA Paper 2017-3519 (2017)]. Correlational methods together with filtering can provide a straightforward measure of the acoustic origin as a function of frequency and thus inform optimal microphone array layout for specific frequency regimes.

This paper summarizes a two-part session, “Acoustics of Supersonic Jets: Launch Vehicle and Military Jet Acoustics,” that took place during the 5th Joint Meeting of the Acoustical Society of America and the Acoustical Society of Japan. The sessions were cosponsored by the Physical Acoustics and Noise Technical Committees and consisted of talks by government and academic researchers from institutions in the United States, Japan, France, and India. The sessions described analytical, computational, and experimental approaches to both fundamental and applied problems on model and full-scale jets and rocket plumes.

Mixing noise from a jet engine originates from an extended spatial region downstream of the nozzle and is partially correlated both spatially and temporally. Previously, the coherence properties in the downstream (axial) direction of the sound field of a tethered military aircraft were investigated, resulting in the identification of different spatial regions based on coherence length [B. M. Harker et al., AIAA J. 54, 1551-1566 (2016)]. In this study, a vertical array of microphones to the side of the jet plume is used to obtain the azimuthal coherence of the sound field. Although multipath interference effects and a limited angular aperture make coherence length calculation impossible, information about upper and lower bounds can be extracted. The measured azimuthal coherence as a function of downstream distance and frequency is then compared to that predicted by sound field reconstructions using multisource, statistically optimized near-field acoustical holography (M-SONAH) [A. T. Wall et al., J. Acoust...

This paper describes the development and presentation of a Science, Technology, Engineering, Arts, and Math (STEAM) workshop for elementary school teachers designed to provide ideas and tools for using acoustics in the classroom. The abundant hands-on activities and concepts in acoustics naturally link science and music in an intuitive way that can assist teachers in moving forward on the STEAM initiative. Our workshop gave teachers an introduction to acoustics principles and demonstrations that can be used to tie in STEAM techniques with Utah State Education Core standards. These hands-on demonstrations and real-world applications provide an avenue to engage students and support learning outcomes. Feedback indicated that the participants learned from and enjoyed the initial implementation of this workshop, though many elementary school teachers did not immediately see how they could integrate it into their curriculum. While additional efforts might be made to better focus the training workshop for the K-...

The five-segment Space Launch System solid rocket motor was recently tested at Orbital ATK. Far-field acoustical measurements were performed at angles between 80° and 120° relative to the rocket exhaust at a distance of roughly 2500 m from the rocket, approximately 800 nozzle diameters. The angular aperture allows for evaluating spatial variation in acoustic properties and a comparison with similar tests in the past, including the 2015 test of the same rocket motor. Although terrain variations introduce uncertainty, an approximate 10 dB change in level is seen throughout the aperture, consistent with previous studies. In addition, at low frequencies a high degree of correlation is seen. Near the peak radiation direction high levels of derivative skewness indicate significant shock content and crackle. This dataset also presents the opportunity to test a new method for processing acoustic vector intensity. [Thomas et al., JASA 137, 3366-3376 (2015)] Comparison with the traditional method shows an increase ...

The primary source of supersonic jet noise originates from the interaction of the turbulent flow with the ambient air. Tam et al. [AIAA Paper 96-1716 (1996)], proposed similarity spectra for a two-source model corresponding to omnidirectional fine-scale turbulence structures (FSS) and directional large-scale turbulent structures (LSS). These empirical similarity spectra agree reasonably with angular variation in mid and far-field spectra of both military and laboratory-scale jets. Near-field measurements of an ideally expanded, Mach 1.8 laboratory-scale jet from the Hypersonic and High-Enthalpy Wind Tunnel at Kashiwa Campus of the University of Tokyo were analyzed. Similarity spectra decompositions adequately describe the turbulent mixing noise as close as 10 jet diameters. Neglecting the effect of the hydrodynamic field, the LSS spectrum provides consistent fits at 15°-40° from the jet axis. A combination of LSS and FSS spectra match the measured spectra at 45°-55°. FSS spectrum matches the spectra at angles greater than 60°, except very close to the nozzle exit plane where there is an overprediction at high frequencies. Comparison of near and mid-field locations may provide insights into propagation radials.The primary source of supersonic jet noise originates from the interaction of the turbulent flow with the ambient air. Tam et al. [AIAA Paper 96-1716 (1996)], proposed similarity spectra for a two-source model corresponding to omnidirectional fine-scale turbulence structures (FSS) and directional large-scale turbulent structures (LSS). These empirical similarity spectra agree reasonably with angular variation in mid and far-field spectra of both military and laboratory-scale jets. Near-field measurements of an ideally expanded, Mach 1.8 laboratory-scale jet from the Hypersonic and High-Enthalpy Wind Tunnel at Kashiwa Campus of the University of Tokyo were analyzed. Similarity spectra decompositions adequately describe the turbulent mixing noise as close as 10 jet diameters. Neglecting the effect of the hydrodynamic field, the LSS spectrum provides consistent fits at 15°-40° from the jet axis. A combination of LSS and FSS spectra match the measured spectra at 45°-55°. FSS spectrum matches the spectra at an...

Acoustic intensity measurements made with multi-microphone probes traditionally use cross-spectral processing methods to estimate pressure and particle velocity. Bias errors become significant as the microphone separation becomes comparable with the acoustic wavelength. However, it has been shown that the phase and gradient estimator (PAGE) method increases probe bandwidth without modifying microphone spacing [Thomas et al. J. Acoust. Soc. Am. 137, 3366-3376 (2015)]. In this study, acoustic intensity is estimated by both the PAGE method and the traditional method across two three-dimensional (3D) intensity probes and three 2D intensity probes. Probe performance is compared in the far field of a broadband noise-radiating loudspeaker located in an anechoic chamber. The results show increased frequency bandwidth using the PAGE method across all probe designs. For 3D probes, intensity level errors were least with a spherical probe. For the 2D probes, the accuracy of intensity level and direction estimates increased with the separation distance of the microphones.Acoustic intensity measurements made with multi-microphone probes traditionally use cross-spectral processing methods to estimate pressure and particle velocity. Bias errors become significant as the microphone separation becomes comparable with the acoustic wavelength. However, it has been shown that the phase and gradient estimator (PAGE) method increases probe bandwidth without modifying microphone spacing [Thomas et al. J. Acoust. Soc. Am. 137, 3366-3376 (2015)]. In this study, acoustic intensity is estimated by both the PAGE method and the traditional method across two three-dimensional (3D) intensity probes and three 2D intensity probes. Probe performance is compared in the far field of a broadband noise-radiating loudspeaker located in an anechoic chamber. The results show increased frequency bandwidth using the PAGE method across all probe designs. For 3D probes, intensity level errors were least with a spherical probe. For the 2D probes, the accuracy of intensity level and direction estimates inc...

Acoustical measurements were made in the very far field during a recent test firing of the five-segment QM-1 Space Launch System solid rocket motor at Orbital ATK. Data were taken using 6.35 mm and 12.7 mm type-1 microphones at three far-field locations to the sideline and aft of the nozzle at a range of 650-800 nozzle diameters. The experiment setup, including the appreciable terrain changes, is first discussed. Spectral and autocorrelation analyses highlight the variation of the noise with respect to observation angle. In addition, high-frequency spectral characteristics and waveform statistics are evidence of the significant nonlinear propagation over the propagation range. Terrain effects and data stationarity during the firing are discussed. This dataset is compared to measurements of other solid rocket motors at closer and farther ranges, including the GEM-60 and the four-segment Shuttle Reusable Solid Rocket Motor.

Acoustic data collected in static rocket tests are typically influenced by ground reflections, but have been difficult to account for. First, the rocket plume is an extended radiator whose directionality results from source correlation. Second, partial coherence of the ground interaction due to atmospheric turbulence can play a significant role, especially for larger propagation distances. In this paper, a finite impedance-ground, single-source interference approach [G. A. Daigle, J. Acoust. Soc. Am. 65, 45-49 (1979)] that incorporates both amplitude and phase variations due to turbulence is extended to distributions of correlated monopoles. The theory for obtaining the mean-square pressure from multiple correlated sources in the presence of atmospheric turbulence is described. The effects of source correlation, ground effective flow resistivity, and turbulence parameters are examined. Finally, the model predictions compared favorably against data from two horizontal firings of GEM-60 solid rocket motors - one involving snow-covered terrain - allowing effective removal of the ground reflection from far-field power spectral densities out to the maximum measurement distance of 1220 m. Close to the motor, more physically realistic corrected spectra are obtained by increasing the modeled fluctuating index of refraction by two orders of magnitude.

Social media is increasingly used to attract the attention of the public to research activities and to promote interest in science worldwide. A concerted effort has been made by the Acoustics Research Group at Brigham Young University to promote acoustics with various methods of enhanced communications. Web page articles were developed with lay-language introductions to the group's research activities, which can be shared directly to social media sites. The group's Facebook page and research Twitter account @BYUAcoustics provide information about current research meetings, publications, and acoustics in the news, which help network with students who may be interested in joining the acoustics program and which keep alumni informed of current events. In addition, local outreach efforts have been expanded through use of social media. A general audience Twitter account @SoundstoAstound has been utilized to connect with students in our descriptive class and K-12 teachers who bring their students to tour our facilities. The overall effectiveness of each system is assessed using webpage statistics, analytics, and perceived success in reaching target audiences. Successes, limitations, and lessons learned are summarized.

An important consideration in characterizing noise from heated, supersonic jets is the crest factor (CF). The large CF in high-speed jet noise is the result of a positively skewed probability density function for the waveform, which translates into infrequently occurring, large-amplitude positive peak pressures. Sufficient system headroom is required in the data acquisition system to provide an accurate representation of these peak pressures and thus avoid clipping or microphone saturation/distortion. But the question remains as to the importance of capturing the single largest pressure out of potentially millions of waveform samples or if a percentile-based CF is adequate. Measurements near a static tactical aircraft reveal CF increases with engine power, with the maximum CF directed upstream of the overall sound pressure level, and a maximum CF of 20 dB at full afterburner. Second, clipping of measured waveforms at different thresholds reveals that a CF definition based on the 99.99 percentile is sufficient to represent overall and band pressure levels to within 0.1 dB and waveform and time-derivative skewnesses to within ~1%. If an estimate of the time-derivative kurtosis is needed within 1% accuracy, then the 99.999 percentile CF is required for headroom estimates.

Development of the next-generation space flight vehicles has prompted a renewed focus on rocket sound source characterization and near-field propagation modeling. Improved measurements of the noise near the rocket plume are critical for direct determination of the noise environment. They are also crucial in providing inputs to empirical models and in validating computational aeroacoustics models. NASA's SP-8072 acoustic load prediction model (1971) is a widely used method for predicting liftoff acoustics. The method implements two Distributed Source Methods (DSM-1 and DSM-2), which predict the loading as the sum of the radiated field from each source distributed along the plume. In this paper, measurements of a static horizontal firing of an Alliant Techsystem (ATK) Orion 50S XLG are analyzed with respect to the historical data that drive the SP-8072 prediction models. Comparisons include total sound power and sound power spectrum, and the distribution of the sound power and sound power spectrum along the length of the plume. Scalar pressure measurements yield reasonable agreement between the Orion-50S XLG data and both methods for undeflected plumes in the original SP-8072. However, development of these comparisons has prompted significant questions regarding the underlying physics of the two methods.