Broadband sound radiated from subsonic rotors

Recent theoretical work on sound sources in subsonic turbomachinery is applied to the correlation of axial-flow fan and compressor noise measurements. Correlations are presented for directivity and sound-power spectra associated with broadband noise. A simple explanation is given to account for the relative amounts of sound power transmitted upstream and downstream from a single-stage fan

Sound radiation in turbulent channel flows

Lighthill’s acoustic analogy is formulated for turbulent channel flow with pressure as the acoustic variable, and integrated over the channel width to produce a two-dimensional inhomogeneous wave equation. The equivalent sources consist of a dipole distribution related to the sum of the viscous shear stresses on the two walls, together with monopole and quadrupole distributions related to the unsteady turbulent dissipation and Reynolds stresses respectively. Using a rigid-boundary Green function, an expression is found for the power spectrum of the far-field pressure radiated per unit channel area. Direct numerical simulations (DNS) of turbulent plane Poiseuille and Couette flow have been performed in large computational domains in order to obtain good resolution of the low-wavenumber source behaviour. Analysis of the DNS databases for all sound radiation sources shows that their wavenumber–frequency spectra have non-zero limits at low wavenumber. The sound power per unit channel area radiated by the dipole distribution is proportional to Mach number squared, while the monopole and quadrupole contributions are proportional to the fourth power of Mach number. Below a particular Mach number determined by the frequency and radiation direction, the dipole radiation due to the wall shear stress dominates the far field. The quadrupole takes over at Mach numbers above about 0.1, while the monopole is always the smallest term. The resultant acoustic field at any point in the channel consists of a statistically diffuse assembly of plane waves, with spectrum limited by damping to a value that is independent of Mach number in the low-M limit

Directivity and sound power radiated by a source under a boundary layer

This paper considers the radiation of sound from compact 2D or 3D sources located in an otherwise rigid wall, bounding a region of fluid flowing parallel to the wall. The sound radiation problem is modeled using a wavenumber decomposition. Numerical results show how the radiated power and directivity depend on the free-stream flow Mach number and the thickness of the boundary layer adjacent to the wall. The numerical model is validated by comparing the sound power and directivity obtained in the limiting case of a thin boundary layer with that obtained from an alternative analytical model in which the flow is uniform and there is slip at the boundary

The design, implementation and evaluation of mass conferencing

There have been attempts to classify and analyse the approaches and techniques of using videoconferencing for teaching and learning. Most classifications include the use of videoconferencing techniques to support lecture‐style delivery to large audiences, or what might be referred to as ‘mass conferencing’. This is often dismissed by sceptics as another gimmick: the real thing is better, or it may be viewed as simply just another didactic approach with little to commend it either in the form of communication or in pedagogical terms. However, the key element in its use is the context within which the mass conferencing is being applied Whatever videoconferencing approaches are employed, it is our view that their successful implementation implies both a clearly defined structure and an operational template. Thus, this paper underlines some of the processes which we have used in mass conferencing. We then evaluate the outcomes, and identify, some themes to be incorporated in successful mass conferencing, including the key factors involved in successful delivery, namely in the preparation, activity, and evaluation stages. In operational terms, the introduction of an external element, beyond the control of course tutors, has highlighted many organizational, pedagogical and technical questions, some of which we address

Modelling of turbulent jets and wall layers: extensions of Lighthill's acoustic analogy with application to computational aeroacoustics

Two extensions to Lighthill’s aeroacoustic analogy are presented. First, equivalent sources due to initial conditions are derived that supplement those due to boundary conditions, as given by Ffowcs Williams & Hawkings. The resulting exact inhomogeneous wave equation is then reformulated with pressure rather than density as the wave variable, and the right-hand side is rearranged using the energy equation with no additional assumptions. Applications to computational aeroacoustics are discussed, and illustrated with examples based on 2D and 3D simulations

A review into the role of voltage gated sodium channels 1.8 and 1.9 in pain states: and medical uses of this knowledge

This review is aimed at discussing the role of voltage gated sodium channels (VGSC) Nav 1.8 and 1.9 in pain states. This involves establishing their role in pain states such as neuropathic and inflammatory pain, and which of these pain states the individual channels impact on and to what effect. Establishing this will involve an exploration of which neurones these channels are located around the body, sensory or nociceptive, as well how their activity impacts on their function. Also discussed will be how the routes of activation of these VGSC impacts on their role in pain sensation and detection within the neurones in which they are found. This will be achieved by the analysis of studies and investigations collected spanning a 30-year period. These experiments use many different techniques that can be compared to draw a strong conclusion on the role of Nav 1.8 and 1.9. This will be used to indicate possible uses of this knowledge in the medical fields such as anaesthesia, suggesting useful implications of the research

Accounting for convective effects in zero-Mach-number thermoacoustic models

This paper presents a methodology to account for some mean-flow effects on thermo-acoustic instabilities when using the zero-Mach-number assumption. It is shown that when a computational domain is represented under the M=0 assumption, a nonzero-Mach-number element can simply be taken into account by imposing a proper acoustic impedance at the boundaries so as to mimic the mean flow effects in the outer, not computed flow domain. A model that accounts for the coupling between acoustic and entropy waves is presented. It relies on a “delayed entropy coupled boundary condition” (DECBC) for the Helmholtz equation satisfied by the acoustic pressure. The model proves able to capture low-frequency entropic modes even without mean-flow terms in the fluctuating pressure equation

Ultrasound-Triggered Release from Multilayered Capsules

No AbstractPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56101/1/804_ftp.pd