A weak-scattering model for turbine-tone haystacking outside the cone of silence

We consider the scattering of sound by turbulence in a jet shear layer. The turbulent, time-varying inhomogeneities in the flow scatter tonal sound fields in such a way as to give spectral broadening, which decreases the level of the incident tone, but increases the broadband level around the frequency of the tone. The scattering process is modelled for observers outside the cone of silence of the jet, using high-frequency asymptotic methods and a weak-scattering assumption. An analytical model for the far-field power spectral density of the scattered field is derived, and the result is compared to experimental data. The model correctly predicts the behaviour of the scattered field as a function of jet velocity and tone frequency<br/

Prediction of the acoustic impedance of duct liners

Recent research which contributes to the prediction of the acoustic impedance of duct liners is reviewed. This review includes the linear and nonlinear properties of sheet and bulk type materials and methods for the measurement of these properties. It also includes the effect of grazing flow on the acoustic properties of materials. Methods for predicting the properties of single or multilayered, point reacting or extended reaction, and flat or curved liners are discussed. Based on this review, methods for predicting the properties of the duct liners which are typically used in aircraft engines are recommended. Some areas of needed research are discussed briefly

Sport psychologists’ experiences of organizational stressors

This study extends stress research by exploring sport psychologists’ experiences of organizational stressors. Twelve accredited sport psychologists (6 academics and 6 practitioners) were interviewed regarding their experiences of organizational stress within their jobs. Content analysis involved categorizing the demands associated primarily and directly with their occupation under one of the following general dimensions: factors intrinsic to sport psychology, roles in the organization, sport relationships and interpersonal demands, career and performance development issues, and organizational structure and climate of the profession. A frequency analysis revealed that academics (ΣAOS = 201) experienced more organizational stressors than practitioners (ΣPOS = 168). These findings indicate that sport psychologists experience a wide variety of organizational stressors across different roles, some of which parallel those found previously in other professions. The practical implications for the management of stress for sport psychologists are discussed

Variation in Egg and Larva Production of the Anchovy, Stolephorus purpureus Fowler, in Kaneohe Bay, Oahu, during 1950-1952

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A weak scattering model for tone haystacking

The scattering of sound by turbulence in a jet shear layer is considered. Spectral broadening or 'haystacking' is the process whereby the turbulent, time-varying inhomogeneities in the flow scatter tonal sound fields, which decreasesthe level of the incident tone, but increases the broadband level around the frequency of the tone. The scattering process is modelled analytically, using high-frequency asymptotic methods and a weak-scattering assumption. Analytical models for the far-field spectral density of the scattered field are derived for two cases: (1) any polar angle including inside the cone of silence; (2) polar angles outside the cone of silence. At polar angles outside the cone of silence, the predictions from the two models are very similar, but using the second model it is considerably simpler to evaluate the far-field spectral density. Simulation results are compared to experimental data, albeit only at a polar angle of 90º. The model correctly predicts the behaviour of the scattered field as a function of jet velocity and tone frequency. Also simulations at other polar angles and a parametric study are presented. These simulations indicate how the 'haystacking' is predicted to vary as a function of the polar angle, and also as a function of the characteristic length, time and convection velocity scales of the turbulence contained in the jet shear layer

The noise and flow characteristics of inverted-profile coannular jets

A basic understanding of the noise reduction mechanisms in shock-free inverted-velocity-profile coannular jets was studied. Acoustic measurements are first conducted in an anechoic facility to isolate the effects of inverted velocity and inverted temperature for coannular jets having constant total thrust, mass flow rate and exit area. To obtain physical explanations of the measured noise changes, several types of experiments are conducted. These include (1) source location experiments using the polar correlation technique, (2) mean flow surveys using a combination pressure/temperature probe, and (3) detailed mean flow and turbulence measurements using a two-point four-channel laser velocimeter. The results from these experiments are presented and discussed in detail. Finally, the measured variations of coannular jet mixing noise with fan-to-primary velocity ratio and static temperature ratio are interpreted by utilizing the results from the various experimental phases in conjunction with the existing Lockheed single jet noise prediction model

The free jet as a simulator of forward velocity effects on jet noise

A thorough theoretical and experimental study of the effects of the free-jet shear layer on the transmission of sound from a model jet placed within the free jet to the far-field receiver located outside the free-jet flow was conducted. The validity and accuracy of the free-jet flight simulation technique for forward velocity effects on jet noise was evaluated. Transformation charts and a systematic computational procedure for converting measurements from a free-jet simulation to the corresponding results from a wind-tunnel simulation, and, finally, to the flight case were provided. The effects of simulated forward flight on jet mixing noise, internal noise and shock-associated noise from model-scale unheated and heated jets were established experimentally in a free-jet facility. It was illustrated that the existing anomalies between full-scale flight data and model-scale flight simulation data projected to the flight case, could well be due to the contamination of flight data by engine internal noise

Induced fragmentation of asteroids during close encounters

We consider the behaviour of rotating binary asteroids as they pass through Earth's Hill sphere, with primary interest in the effect the tidal force on the interaction between the two components of the binary and their post-encounter trajectories. We focus on contact binary asteroids bound by a regolith bridge, using both direct numerical simulation and analytical approaches to investigate the sensitivity of the system to different parameters. We find that the system is most sensitive to the angle between the binary pair and the orbital path, having a significant impact upon the energy change during a fragmentation event. We also give the results of some basic simulations of a deflection attempt on such an object