BYU ARG Gets Gatlinged!

Large-eddy simulations (LES) have been shown to reproduce the flow and acoustic fields of laboratory-scale jets with increasing accuracy. However, measurements of full-scale, highperformance military aircraft reveal phenomena that are not widely seen at laboratory scales. Recent modifications to LES methods allow for simulations of jets operating at a high temperature ratio, in a similar regime as military aircraft operating at afterburner. This work applies coherence analyses that have been previously used to study the jet noise field produced by military aircraft to the LES of a highly-heated, laboratory-scale jet. The coherence of the complex pressures along a near-field line approximately parallel to the shear layer shows evidence of four distinct field regions. The coherence between this line and complex pressures along the simulated jet lipline provide source regions in the jet plume corresponding to each field region. Differences in how information is transferred from the flow to the field suggests that the source regions represent different noise production mechanisms. The field regions compare favorably to some spatiospectral lobe features observed in measurements of an F-35B aircraft operating at afterburner, though do not reproduce all of the phenomena present in the aircraft’s jet noise field.

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.

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.

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.

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.

Bias errors for two-dimensional active acoustic intensity using multi-microphone probes have been previously calculated for both the traditional cross-spectral and the Phase and Amplitude Gradient Estimator (PAGE) methods [Whiting, Lawrence, Gee, Neilsen, and Sommerfeldt, J. Acoust. Soc. Am. 142, 2208–2218 (2017)]. Here, these calculations are expanded to include errors due to contaminating noise, as well as probe orientation. The noise can either be uncorrelated at each microphone location or self-correlated; the self-correlated noise is modeled as a plane-wave with a varying angle of incidence. The intensity errors in both magnitude and direction are dependent on the signal-to-noise ratio (SNR), frequency, source properties, incidence angles, probe configuration, and processing method. The PAGE method is generally found to give more accurate results, especially in direction; however, uncorrelated noise with a low SNR (below 10–15 dB) and low frequency (wavelengths more than 1/4 the microphone spacing) can yield larger errors in magnitude than the traditional method—though a correction for this is possible. Additionally, contaminating noise does not necessarily impact the possibility of using the PAGE method for broadband signals beyond a probe's spatial Nyquist frequency.