External Acoustic Field Research Articles

On the acoustic–director interaction in the smectic A phase

A model was previously proposed for the interaction energy between an acoustic field and the local nematic director. The consistency of this model was verified through nuclear magnetic relaxation and optical experiments. The model was later extended to the smectic A phase, despite the fact that the smectic essence of the problem was never included in the interaction process. In this work we investigate details of this interaction through the inclusion of elemental features of the smectic phase. We show that the acoustic–director interaction can be enhanced if the external acoustic field matches an eigenmode of the smectic system.

Development of an Improved Mode of Heat Transfer of a Hydrocarbon Heat Carrier under a Supercritical Pressure in an External Acoustic Field of a Standing Wave Formed by Thermoacoustic Self-Oscillations of Pressure

Development of an Improved Mode of Heat Transfer of a Hydrocarbon Heat Carrier under a Supercritical Pressure in an External Acoustic Field of a Standing Wave Formed by Thermoacoustic Self-Oscillations of Pressure

Frequency Dependence of the Amplitude of Domain-Wall Oscillations in an Acoustic Wave Field

The velocity of oscillatory motion of domain walls is investigated as a function of the parameters of a magnetic material and an external acoustic field. The dependence of the amplitude of domain-wall oscillations on the frequency of an external acoustic wave is determined. It is found that this dependence exhibits a resonant behavior.

Maximum Size of a Gas Bubble in the Regime of Automodel Pulsation

A complete symmetry group for the Rayleigh equation used as a basis for the theoretical description of acoustic cavitation is found, which allows the form of an external drive giving rise to internal dynamic symmetry in gas bubble pulsation to be determined. The efficiency of bubble extension under the action of a periodically prolonged scale-invariant external acoustic field is studied. It is demonstrated that this action, having the form of a train of shock waves, does not lead to a significant decompression. This circumstance significantly reduces the probability of damaging biological tissues as a result of cavitation caused by the extension phase of a shock pulse.

Interaction of a Supersonic Turbulent Wake with Acoustic Disturbances

The effect of an external acoustic field on disturbances in a supersonic turbulent wake is investigated experimentally.

Linear Solutions for the Emission of Screech Tone in Supersonic Jets

The article presents a critical analysis of the solutions of the linear screech tone problem obtained by the author in the 1970s and compares them with modern experimental results. The comparison shows that the proposed model, despite its many simplifications, on the whole provides a faithful description of the screech tone phenomenon, including fine perturbed flow structures in a pulsating jet and its external acoustic field. The modified formula for the screech tone frequency fits the experimental observations.

On the interaction between a charged drop and an external acoustic field

An interaction between capillary oscillations of a charged drop and an external acoustic field is investigated under conditions in which nonlinear components of the acoustic pressure on the drop surface may be neglected. It is shown that equations describing the temporal evolution of modes of the capillary waves in this case may be either the Mathieu-Hill equations or ordinary inhomogeneous equations of the second order describing forced oscillations. In both cases, the drop instability (of a parametric or resonance type) may result in its disintegration due to deformation caused by the acoustic field at its own drop charge, subcritical in the sense of the Rayleigh criterion.

Optical Mie scattering to observe single cavitation bubble dynamics

It is often advantageous to know precisely the instantaneous response of bubbles to an external acoustic field. One technique to enable such observations consists of detecting the time-resolved optical scattering of an incident laser beam from a bubble. For visible laser light and bubble radii on the order of 1–100 microns, reflection, refraction, internal interference, and diffraction must all be taken into account, and the scattering so described is named after Gustav Mie. Physical principles and the mathematical development will be discussed. Several specific applications will be presented and the results discussed. Finally, a brief list of ‘‘do’s and don’ts’’ for the potential user will be discussed.

The influence of curvature on the sound radiated by vibrating panels

The influence of curvature on sound radiation by a rectangular panel is investigated by considering the situation where the panel is set in an infinite cylinder. As in the flat panel case, acoustic effects may be characterized by a set of modal impedances, whose relationship to the corresponding flat panel terms is calculated for large cylinder radius. It is found that the impedances arising from the external acoustic field tend to their flat panel counterparts, but those associated with the internal field only do so under suitable conditions on the cylinder internal acoustic damping. Specifically, the interior wall must be sufficiently hard that it effectively appears rigid around the panel, but sufficiently dissipative that reflected ray and near-field line-of-sight contributions to the impedance are negligible. The conditions are investigated in detail for parameters appropriate to a wide-body civil aircraft, and curvature is found to be potentially important for the mode classes of interest.

Study of the transition regime of forced capillary breakup of a liquid jet

The results of a study of capillary breakup of thin liquid jets subjected to a random external acoustic field are reported.

Vortex sound in 2D: ‘‘vortex-force’’ and ‘‘vorticity-alone’’ forms

In the contiguous method [J. Acoust. Soc. Am. 36, 830–832 (1964)] an incompressible inviscid flow causes pressure or velocity perturbations, pinc or u, on geometrically distant surface (cylinder) that drives the contiguous external acoustic field. Solid surfaces are replaced by some appropriate vortex image system. The far field sound pressures are found to be p(x) =[1/√(8π)] [(ρω1/2)/(x1/2c1/2)]I*D for dipole sound, with c−3/2I*Q for quadrupoles, ρ=density, c=sound speed, I=sinusoidal source term (or its Fourier component or transform) of frequency ω, f(t)*≡f(t−x/c). In terms of vortex force, −ρ(ζΛu), where ζ=∇Λu=vorticity, ∇2(pinc+ρu2/2)=−ρ∇⋅(ζΛu) leads to ID=−∫(ζΛu)’x dS(y), with f(t)’≡∂f/∂t and IQ=−∫yx(ζΛu)‘x dS(y). For vorticity alone, use u=∇ΛB, where ∇2B=−ζ, to get ID=∫(yΛζ,‘)x dS(y) and IQ =∫(1/2)yx(yΛζ‴) x dS(y). (In 3D, constants in the integrals are 1, 1 and 1/2, 1/3, respectively.) The implications of these all being integral results are discussed; while the vortex force −ρ(ζΛu) is a local flow property, (yΛζ) is not.

The role of acoustic radiation force in contrast enhancement techniques using bubble-based ultrasound contrast agents

The movement of bubbles in an acoustic field has recently been used to manipulate bubbles for the purpose of contrast enhancement in medical applications. Some ultrasound contrast agents consist of stabilized microbubbles which, when exposed to an acoustic field, can be collected at specific points in space and may be moved by translating the field. One application for this type of bubble manipulation is the collection of bubbles within the urinary tract for urinary reflux diagnosis. Experiments conducted on sacrificed dogs indicate that bubbles can be moved in a controlled fashion within the bladder using external acoustic fields. In addition, acoustic radiation force could be used to overcome hydrodynamic forces in flowing blood. Bubbles could be pushed to a vessel wall to collect contrast and when the sound field was turned off, a bolus of contrast agent would reenter the flow for measurement of tissue perfusion. In preliminary experiments, a bolus of bubbles was created in blood flowing through dialysis tubing. This paper will review these experimental findings and present an examination of the mechanisms involved in each application. [Work supported in part by USPHS Grant No. DK-42290.]

Simulation of drop dynamics in an acoustic positioning chamber

To support experiments scheduled for the First United States Microgravity Laboratory (USML-1) shuttle mission, experimental and computer simulation methods have been developed which allow ground-based investigation of the translational, rotational, and vibrational motions of single and dual liquid drops in an external acoustic field in a microgravity environment. The acoustic fields used are the 3-D orthogonal resonant modes of a rectangular chamber. Hardware and software development are described in detail. Results for the translation of single and dual drops are presented, and semi-automated schemes for controlled translation are proposed, tested, and evaluated.

Simulation of drop motion in an acoustic positioning chamber.

To support experiments scheduled for the First United States Microgravity Laboratory (USML-1) shuttle mission, experimental and computer simulation methods have been developed that allow ground-based investigation of the translational, rotational, and vibrational motions of single and dual liquid drops in an external acoustic field in a microgravity environment. The acoustic fields used are the 3-D orthogonal resonant modes of a rectangular chamber similar to the near ambient chamber of the drop physics module which will fly on USML-1. Results for the translation of two drops, and oscillation and rotation control of single drops will be presented. A software package allowing the simulation of actual manipulations to be performed for the flight experiments will be displayed. [Work supported by NASA through JPL Contract 958722.]

Structure of artificial disturbances induced by an external acoustic field in a supersonic boundary layer

The wave structure of the artificial disturbances generated by an external acoustic field in a supersonic boundary layer is investigated. The disturbances are classified with respect to phase velocity. Disturbances whose phase velocity in the direction of flow is greater than unity and waves located at the boundary of the discrete and continuous spectra are detected.

Investigation of supersonic isobaric submerged turbulent jets

Turbulent supersonic submerged air jets have been investigated on the Mach number interval Ma = 1.5–3.4 and on the interval of ratios of the total enthalpies in the external medium and the jet i0 = 0.01 – 1. Oxyhydrogen jets with oxidizer ratios α = 0.3–5 flowing from a nozzle at Mach numbers Ma = 1 and 2.4 have also been investigated. When α < 1 the excess hydrogen in the jet burns up on mixing with the air. Special attention has been paid to obtaining experimental data free of the influence on the level of turbulence in the jet of the initial turbulence in the nozzle forechamber, shock waves occurring in the nozzle or in the jet at the nozzle exit, and the external acoustic field. The jet can be divided into two parts: an initial part and a main part. The initial part extends from the nozzle exit from the section x′, in which the dimensionless velocity on the jet axis um = ux/ud = 0.75. Here, ux is the velocity on the jet axis at distance x from the nozzle exit, and ua is the nozzle exit velocity. The main part of the jet extends downstream from the section x′. For the dimensionless length of the initial part xm′ = x′/da, where da is the diameter of the nozzle outlet section, empirical dependences on Ma and i0 are obtained. It is shown, that in the main part of the jet the parameters on the flow axis — the dimensionless velocity and temperature — vary in inverse proportion to the distance, measured in units of length x′, and do not depend on the flow characteristics which determine the length of the initial part of the jet. The angles of expansion of the viscous turbulent mixing layer in the submerged heated or burning jet increase with decrease in i0 and Ma and are practically independent of the afterburning process.

Influence of an external acoustic field on the temperature of an arc-discharge plasma

The influence of an external acoustic field on the temperature of an air-discharge plasma in the channel of a sectional plasmatron is investigated.

Sound radiation from ducts: Theory and experiment

The paper deals with a method of prediction of noise radiated from finite length ducts with arbitrary shape. The computation of the internal and external acoustic field is based upon a new variational formulation by integral equations. Numerical results of far and near field radiation patterns are compared with experimental data for various higher order mode source conditions.

Excitation of natural oscillations in a boundary layer by an external acoustic field

Excitation of natural oscillations in a boundary layer by an external acoustic field

Interaction between a supersonic boundary layer and acoustic disturbances

The development of disturbances in a boundary layer that have been induced by an external acoustic field are investigated. The problem is considered in the linear formulation. It is shown that the oscillations inside the supersonic boundary layer can have several times the intensity of the external disturbances. The susceptibility of the boundary layer to the acoustic disturbances increases with increasing Mach number. Cooling of the surface leads to a small decrease in the intensity of the longitudinal velocity oscillations in the layer. The effect of the parameters of the acoustic wave is considered, i.e., the effect of the frequency and phase velocity on the development of the disturbances.