Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 60, Number 11
Friday–Saturday, October 16–17, 2015; Tempe, Arizona
Session D9: Nonlinear Dynamics |
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Chair: Avishek Kumar, Arizona State University Room: MU224 |
Friday, October 16, 2015 1:50PM - 2:02PM |
D9.00001: Acoustic Environment of an F-35B Aircraft During Vertical Landings Brent Reichman, Kent Gee, Tracianne Neilsen Measurements of the sound field near an F-35B during vertical landing operations are reported. Data are presented and discussed from the approach, hover, and descent of the aircraft, and compared with ground run-up measurements. Overall levels are comparable to published values for the F-35A at 50{\%} engine thrust ratio during ground run-ups. One-third-octave spectra are also presented, and spectra from various stages of the approach and landing are compared. Changes in the spectral shape during the landing process are discussed and impingement is presented as a possible cause of these changes. [Preview Abstract] |
Friday, October 16, 2015 2:02PM - 2:14PM |
D9.00002: Using Helium as the Working Fluid in Thermoacoustic Engines Nathaniel Wells, Bonnie Andersen The efficiency of thermoacoustic engines can be improved by using helium as the working fluid because it reduces viscous losses, has a higher thermal conductivity and speed of sound. The engine in this study has a bottle-shaped resonator. The neck consists of a brass cylinder, closed at the top end and a copper cylinder, open at both ends, with copper mesh screens heat exchangers between them (ID of 1.91cm and total length of 5.24 cm). A small amount of steel wool (20 mg) functions as the stack. The neck opens into an aluminum cavity (10 cm long with an ID of 4.13 cm). A combination of two types of heat-shrink tubing and Teflon were used to connect the brass and copper pieces. The engine was evacuated of air and backfilled with helium as much as the setup would tolerate. Using an input power of 14.8 W over intervals of 0.5-3 hours, it was observed that the frequency decreased in time, indicating that the helium was leaking out slowly. From the frequency data, the volume fraction of helium was calculated, indicating that the engine was able to achieve 64{\%} volume fraction of helium and decreased to 6{\%}. The intensities of the sound over this range of volume fractions averaged at 155 W/m$^{\mathrm{2}}$ compared with air at an average of 118 W/m$^{\mathrm{2}}$. [Preview Abstract] |
Friday, October 16, 2015 2:14PM - 2:26PM |
D9.00003: Reduction of Stochastic Duffing Equation with Frequency Drift Jason Yalim, Bruno D. Welfert, Juan M. Lopez The statistical response of a periodically forced spring-mass system with cubic stiffness and Brownian frequency drift is numerically analyzed using a stochastic reduction. The spring-mass system is subject to a constant, small positive damping and a slow-pass linear frequency ramping for various cubic stiffness values including cases where unbounded solutions can occur for certain initial conditions. The stochastic reduction calculations are compared to corresponding Monte Carlo simulations and it is shown that the ensemble will converge to the stochastic reduction results for given nontrivial Brownian tuning parameters $\sigma$. Due to the construction of the reduction, the numerical integration is deterministic which provides a relatively cheap way to approximate the behavior of the stochastic system. The results also provide guidance on how to reduced a stochastic partial differential equation system. [Preview Abstract] |
Friday, October 16, 2015 2:26PM - 2:38PM |
D9.00004: Quantitative nonlinearity in subsonic and supersonic model-scale jet noise. Kyle Miller Understanding the impact of jet noise, including annoyance due to crackle, can be improved by quantifying the nonlinearity in a signal with a single-microphone measurement. An ensemble-averaged, frequency-domain version of the generalized Burgers equation has been used to find a quantitative expression for the change in sound pressure level spectrum, $L_{p}$, with distance, $r$, due to the separate effects of geometric spreading, absorption, and nonlinearity. The nonlinear term, based on the dimensionless nonlinearity indicator known as ``$Q/S$,'' has been used to characterize the frequency-dependent nonlinearity as a function of angle and distance in subsonic (Mach-0.85), overexpanded (Mach-1.8), and ideally expanded (Mach-2.0) model-scale jet data. Analyses show that nonlinear effects in the Mach-2.0 data are about twice as strong as those in the Mach-1.8 data, but such effects are completely absent in the Mach-0.85 data. [Preview Abstract] |
Friday, October 16, 2015 2:38PM - 2:50PM |
D9.00005: Coherence lengths of high-performance military aircraft noise radiation in the near field Blaine Harker, Tracianne Neilsen, Kent Gee Coherence analyses of pressure measurements on a ground-based array of microphones of noise from a tethered F-22A provide insights into the sound field variation with position and engine conditions which are fundamental in the continued development of more complete jet noise models. Among the features of jet noise illuminated by a coherence analysis are estimates of spatial coherence lengths as a function of frequency and location. The field coherence lengths are utilized in analyzing the coherence lengths of equivalent source distributions obtained from applying a specialized beamforming algorithm (DAMAS-C) to the ground-based array data. The cumulative results of these investigations provide a deeper understanding of jet noise source features and provide a full-scale military jet noise benchmark that should be considered when evaluating laboratory-scale jet studies and computational simulations of jet noise. [Preview Abstract] |
Friday, October 16, 2015 2:50PM - 3:02PM |
D9.00006: Acoustic hysteresis of varying cavity length of a bottle-shaped thermoacoustic prime mover with a neck to cavity ratio of 1:10 Emily Jensen, Bonnie Andersen A previous study showed hysteresis in transition regions to overtones of bottle-shaped thermoacoustic prime movers with a neck to cavity diameter ratio of 1:2.4 while varying the cavity length. Hysteresis regions were studied with a neck to cavity diameter ratio of 1:10. The device consisted of a neck (5.15 cm long, 0.75'' ID) with a heating element around it and a cavity (ID 3.75'') with a sliding piston, allowing the cavity length to be varied up to 38 cm long. Copper mesh was used for the heat exchangers and were located about 30{\%} away from the top of the neck and 16 mg of steel wool served as the stack. A pressure sensor was connected to the center of the piston to measure acoustic pressure at the bottom of the cavity. Acoustic pressure, frequency, and hot and cold temperatures were recorded while both increasing and decreasing the cavity length from about 2 cm to 38 cm in increments of 0.2 cm over time intervals of 20 s with an input power of 10.5 W. Three transitions to overtones occurred at 6.8, 15.2, and 27.4 cm while pulling the piston out and at about 25.2, 15.6, and 6.0 cm while pushing the piston in. Frequencies and transition regions agreed with expected values. Both hot temperature and acoustic pressure increased during transition regions. This could be caused from multiple acoustic waves being produced. [Preview Abstract] |
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