This paper reviews the current state of knowledge of several classes of acoustic streaming. Acoustic streaming is classified based on the different mechanisms by which it is generated. For each category, the main achievements in terms of analysis, experimental work, and numerical simulation are described. An order of magnitude analysis, applicable to all types of acoustic streaming, is also given. This provides an additional means to classify acoustic streaming as either slow or fast, depending on the amplitude of the primary driving mechanism. The significant lack of understanding in the general area of fast streaming is noted, and the importance of the use of direct numerical simulations in the study of nonlinear streaming is emphasized. The paper concludes with a summary of the many challenges that are still faced by researchers in this field. The authors are pleased to contribute this paper in honor of Alan Powell's significant contributions to acoustics on the occasion of his eightieth birthday.

A conceptual framework for understanding the needs and concerns of different stakeholders. Trust Requirements in E-BusinessTrust in information services and technologies has become an increasingly important issue. The development of trust between businesses, consumers, and other stakeholders is seen as crucial to the expansion of e-business markets and the full exploitation of technological developments in this area [3,4,10]. However, the way in which trust may be gained in this context is not yet well understood. Requirements relating to trust are seen from many different perspectives by different stakeholders, and often expressed in different terms. There is therefore a need for a common FERRUCIO SARDELLA

This paper describes a method to connect the measured spectral density in the acoustic far field with the wavenumber/frequency spectrum of the near field fluctuations that produce the noise. A relationship is first derived between the far field spectral density and the wavenumber/frequency spectrum of the pressure fluctuations on a cylindrical surface surrounding the jet in the near field. Measurements of the far field spectral density are then decomposed into contributions from the Large Scale Similarity (LSS) and Fine Scale Similarity (FSS) spectra. The near field wavenumber/frequency spectrum associated with the LSS spectral density alone is then determined. It is shown to have a very similar form for a range of jet operating conditions and Strouhal numbers. This form is consistent with an instability wave or wave packet model. Since both subsonic and supersonic jet exit conditions are examined, it is argued that the noise radiation in the peak radiation directions is controlled by the axial evolution of the turbulent large scale structures and is not associated with a combination of source convection and mean flow refraction effects.

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This paper provides a review of the stability characteristics of high speed jets. These characteristics not only play a role in the transition of jet flows to turbulence, in the traditional sense of hydrodynamic stability theory, but also are key to understanding the behavior of large scale turbulent structures in the jet. They are also an important component in understanding the noise radiation by high speed jets. The paper begins with the development of the linear stability equations and then reviews the classes of instability waves in a jet, modeled as a cylindrical vortex sheet. Finite shear layer thickness effects are then discussed. This includes a review of numerical methods for the solution of the stability equations. The effects of jet Mach number and temperature are then presented. Additional topics considered include, the effects of mean flow divergence, the effect of Reynolds number, and the effect of the jet's geometry. Finally, the nature of absolute instabilities in jet flows is described, both from an analytical viewpoint as well as applications.