Selected Publications
Noise from a tactical aircraft can impact operations due to concerns regarding military personnel noise exposure and community annoyance and disturbance. The efficacy of mission planning can increase when the distinct, complex acoustic source mechanisms creating the noise are better understood. For each type of noise, equivalent acoustic source distributions are obtained from a tied-down F-35B operating at various engine conditions using the hybrid method for acoustic source imaging of Padois, Gauthier, and Berry [J. Sound Vib. 333, 6858–6868 (2014)]. The source distributions for the distinct noise types are obtained using different sections of a 71 element, ground-based linear array. Using a subarray close to the nozzle exit plane, source distributions are obtained for fine-scale turbulent mixing noise and broadband shock-associated noise, although grating lobes complicate interpretations at higher frequencies. Results for a subarray spanning the maximum sound region show that the multiple frequency peaks in tactical aircraft noise appear to originate from overlapping source regions. The observation of overlapping spatial extent of competing noise sources is supported by the coherence properties of the source distributions for the different subarrays.
Measurements of full-scale high-performance military aircraft reveal phenomena that are not widely seen at laboratory scales. However, recent modifications to large eddy-simulation (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 as well as along the nozzle lip line shows evidence of distinct noise production mechanisms that transfer information differently from the flow to the field. A phenomenological comparison between the LES and measurements of an afterburning F-35 aircraft is then made. Although the LES is not run at the exact same conditions as the aircraft and does not reproduce all of the phenomena present in the aircraft’s jet noise field, differences between noise production mechanisms observed in the LES may describe some of the spatiospectral lobe phenomena observed in the measurements of the F-35.
The traditional method for intensity-based sound power estimates often used in engineering applications is limited in bandwidth by microphone phase mismatch at low frequencies and by microphone spacing at high frequencies. To overcome these limitations, the Phase and Amplitude Gradient Estimator (PAGE) method [Gee, Neilsen, Sommerfeldt, Akamine, and Okamoto, J. Acoust. Soc. Am. 141(4), EL357–EL362 (2017)] is applied to sound power for a reference sound source, a blender, and a vacuum cleaner. Sound power measurements taken according to ISO 3741:2010 (2010) are compared against traditional- and PAGE-processed intensity-based sound power estimates measured according to ANSI S12.12-1992 (R2017). While the traditional method underestimates the sound power at the spatial Nyquist frequency by 7–10 dB, the PAGE-based sound power is accurate up to the spatial Nyquist frequency, and above when phase unwrapping is successful.
A challenging part of an academic’s job is developing productive research relationships as a mentor. This paper presents ideas for improving a mentor’s effectiveness at different mentorship phases, from the relationship’s initiation through its redefinition upon graduation. These ideas stem both from personal experiences with undergraduate and graduate students and from a review of relevant literature.
In this paper, a wavepacket ansatz is used to create an analytical model for the jet noise radiation from a high-performance military aircraft. Unlike other equivalent, acoustics-based wavepacket source models, this one is designed to match the measured acoustic vector intensity at a number of positions in the jet near field for both military power and afterburner engine conditions. The complex pressure of a line source is defined according to an analytical hyperbolic tangent wavepacket model and Rayleigh integration is used to find the pressure, particle velocity, and time-averaged intensity at observer locations. A cost function developed from the modeled and measured acoustic intensity vectors is used in a simulated annealing algorithm to find the optimal wavepacket parameters. Although this source modeling approach neglects some source characteristics, it also provides a relatively simple equivalent source modeling methodology that provides insights into tactical jet noise radiation.
The ANSI S3.4-2007 standard gives a method for calculating the predicted loudness of stationary sounds for an average listener. Glasberg and Moore (2002) provide an extension of the method to time-varying sounds. The mathematical structure of the excitation in the loudness calculation is amenable to significant acceleration in MATLAB by expressing the entirety of the calculation representing the cochlear filtering process in terms of matrices and array operations. Thus, procedures to achieve rapid processing of loudness are set forth. The procedures explained here are also applicable to other metrics in this family including those in ISO 532-2 and the upcoming ISO 532-3. Further steps for obtaining faster than real-time processing of loudness employing approximation are explained.