Selected Publications
Sonic boom measurements from recent flight tests have provided an opportunity to investigate effects of microphone installation on sonic boom waveforms, spectra, and metric levels in support of NASA X-59 flight test planning. While those flight tests used N-wave aircraft (F-18s), modeling studies were also conducted using source characteristics for a shaped low-boom aircraft. Of particular interest were the effects of receiver height on boom waveforms and metrics at elevated receiver positions, microphone installation, and local ground cover type. Reductions of more than 2 dB in A-weighted sound exposure level and perceived level were shown for 1.6 ft (0.48 m) microphone heights for 35º ray elevation angle. Measured and modeled results are described in this letter.
A downside of landing first-stage boosters of orbital-class launch vehicles, such as the Falcon 9, is the sonic boom associated with reentry and landing. To assess the potential impact of these sonic booms and compare them to launch and landing operations, acoustic data from a Falcon-9 launch and booster landing at Van-denberg Space Force Base are analyzed. The data were collected near Lompoc, CA, at a station 8 km away from the landing site. Because of the booster shape and landing orientation, the measured waveform contains three shocks (a triple boom), rather than the two associated with a traditional N-wave. Waveform and spectral characteristics are examined and various metrics, including A-weighted Sound Exposure Levels, are calculated and compared with those of the launch and landing noise.
Because the noise source mechanisms and radiation properties associated with high-thrust, tactical jet engines are not fully understood, analysis of full-scale measurements can shed significant insight on such characteristics. One method for examining spectral data is to compare them to empirical models for jet noise spectra. This paper compares measured near-field spectra from a T-7A-installed GE F404-103 engine with analytical similarity spectra for fine-scale mixing noise, large-scale mixing noise, and broadband shock-associated noise. This initial similarity spectra analysis enables the determination of spatial trends in overall level and peak frequency and the relative importance of each type of noise radiation as a function of location. This approach can be used to gain insights on spatial and frequency trends of noise source mechanisms for different engine conditions and for rapid comparisons to other aircraft and jets of other scales and conditions.
Multisource statistically-optimized near-field acoustical holography and hybrid beamforming are two inverse techniques that have been successfully used to reproduce sound fields from limited measurements of military aircraft. These methods solve the inverse problem through different means but arrive at the same conclusion. In this paper, the performance of each method is compared to the same baseline measurement. It is found that while both perform well at mid-range frequencies, holography excels at lower frequencies and beamforming at higher frequencies. The spatial Nyquist frequency imposes a soft limit on the accuracy of field reconstructions and limits the usable frequency range.
The Saturn V is a monument to one of mankind's greatest achievements: the human Moon landings. However, online claims about this vehicle's impressive acoustics by well-meaning individuals are often based on misunderstood or incorrect data. This article, intended for both educators and enthusiasts, discusses topics related to rocket acoustics and documents what is known about the Saturn V's levels: overall power, maximum overall sound pressure, and peak pressure. The overall power level was approximately 204 dB re 1 pW, whereas its lesser sound pressure levels were impacted by source size, directivity, and propagation effects. As this article is part of a special issue on Education in Acoustics in The Journal of the Acoustical Society of America, supplementary Saturn V-related homework problems are included.
This paper summarizes Brigham Young University’s (BYU) participation in NASA’s 2019 sonic boom data collection campaign in California, USA. Dubbed “Carpet Determination In Entirety Measurement” (CarpetDIEM) Phase I, the program was designed to measure conventional cruise booms across a widespread time-synchronous array, at the site where initial acoustical testing of the X-59 low-boom supersonic aircraft is planned. BYU deployed a total of 11 portable data acquisition systems across 10 nautical miles and tested a variety of microphone and data acquisition configurations. This paper describes both technical and logistical lessons learned at CarpetDIEM Phase I that can help with future X-59 test design including acquisition hardware comparison and local measurement effects, including turbulence.