Effect Of Acoustic Oscillations Research Articles

Effect of Acoustic Oscillations on Non-Equilibrium State of Magnetic Domain Structure in Cubic Ni2MnGa Single Crystal.

Magnetic hysteresis is a manifestation of non-equilibrium state of magnetic domain walls trapped in local energy minima. Using two types of experiments we show that, after application of a magnetic field to a ferromagnet, acoustic oscillations excited in the latter can "equilibrate" metastable magnetic domain structure by triggering the motion of domain walls into more stable configurations. Single crystals of archetypal Ni2MnGa magnetic shape memory alloy in the cubic phase were used in the experiments. The magnetomechanical absorption of ultrasound versus strain amplitude was studied after step-like changes of a polarizing magnetic field. One-time hysteresis was observed in strain amplitude dependences of magnetomechanical internal friction after step-like variations of a polarizing field. We distinguish two ingredients of the strain amplitude hysteresis that are found in the ranges of linear and non-linear internal friction and show qualitatively different behavior for increasing and decreasing applied polarizing fields. The uncovered effect is interpreted in terms of three canonical magnetomechanical internal friction terms (microeddy, macroeddy and hysteretic) and attributed to "triggering" by acoustic oscillations of the irreversible motion of domain walls trapped in the metastable states. To confirm the suggested interpretation we determine the coercive field of magnetization hysteresis through the measurements of the reversible Villari effect. We show that the width of the hysteresis loops decreases when acoustic oscillations in the non-linear range of domain wall motion are excited in the crystal. The observed "equilibration" of the magnetic domain structure by acoustic oscillations is attributed to the periodic stress anisotropy field induced by oscillatory mechanical stress.

Effect of low-frequency vibrations on the characteristics of the diffusion flame

The paper considers the effect of low-amplitude acoustic oscillations on the temperature field in the flame formed during the combustion of kerosene gasoline. As a result of using the IRT-method, sets of thermograms of the combustion process were obtained. For the obtained thermograms, the distribution of high-temperature inhomogeneities in the flame plume was analyzed. As a result, it was obtained that the effect of acoustic oscillations on the flame plume causes a change in the height of the plume, a change in the combustion rate. When analyzing the spectra of temperature changes, characteristic pulsations, which are different, depending on the flame zone, were observed. Analysis of the distribution of temperature inhomogeneities under different modes of exposure to pressure pulsations, allowed to identify the characteristic modes in which there is a change in the geometric dimensions of the temperature inhomogeneity distribution zone.

Temporal analysis of a power-law liquid sheet in the presence of acoustic oscillations

The instability of a non-Newtonian liquid sheet in the presence of acoustic oscillations is investigated theoretically. The power-law model is used to describe the viscosity of the non-Newtonian liquid. The corresponding dispersion relation is obtained by linear analysis. The effects of the mean velocity of the gas, the oscillation amplitude, the oscillation frequency, and the gas density on the instability of the power-law liquid sheet are studied. The results show that the shear-thickening liquid sheet is more unstable than Newtonian and shear-thinning liquid sheets when the effects of acoustic oscillations are considered. In particular, a second unstable region appears on the shear-thickening liquid sheet at a low oscillation frequency. Especially, for the shear-thinning liquid sheet, there is a second unstable region in the dispersion curve at a high mean gas velocity. A third unstable region appears on the shear-thinning liquid sheet at a high gas density in the presence of acoustic oscillations. The unstable range of the Newtonian liquid is always the widest among these liquids.

The effect of acoustic oscillations on diffusion combustion of methane

Aspects of ecological safety related to the combustion of hydrocarbons—in particular, the demand for reducing the content of toxic compounds in combustion products—are extremely topical. In addition, there is still important task of increasing the efficiency of using all kinds of fuel, including hydroarbons. One possible mechanism of controlling combustion processes—namely, the effect of acoustic perturbations on the diffusion combustion of methane—has been considered. The influence of acoustic oscillations on the characteristics of diffusion flame has been studied, and the dependence of the concentration of nitrogen oxides in the combustion products on the acoustic signal frequency has been determined.

Experimental Investigation of the Evaporation of Droplets in Axial Acoustic Fields

The effect of axialacoustic Ž elds on the evaporationof individualdroplets is investigatedboth experimentallyand theoretically. A setup was developed in which images of droplets moving through an acoustic Ž eld were acquired using a state-of-the-art, high-speed, intensiŽ ed video system. The evaporation rates of droplets were determined from the droplet diameters measured from these images. Experimental investigations using methanol droplets showed that the presence of an acoustic Ž eld signiŽ cantly enhances the evaporation of droplets. The evaporation rate is a strong function of the acoustic amplitude, but increases only slightlywith frequency. The effect of acoustic oscillations on water and methanol droplet evaporation was theoretically modeled by numerically integrating the differential equations for droplet mass, momentum,and heat transfer. The model uses quasisteady correlations for momentumheat and mass transfer. The model predicted the measured trends correctly. However, the quantitative agreement of these predictions with the experimental data depends strongly on the correlations for Nussult and Sherwood numbers used to model the energy and mass transfer, respectively.

An Experimental Investigation of the Behavior of Droplets in Axial Acoustic Fields

This paper describes an experimental investigation of the behavior of water droplets in axial acoustic fields. It was motivated by the increasing interest in the use of pulsations to improve the performance of energy intensive, industrial processes. The presence of an acoustic field is believed to enhance heat and mass transfer to and from the droplets, probably because of the relative motion between the droplets and the gas phase. This relative motion is characterized by the ratio of the amplitude of the oscillatory droplet velocity to that of the acoustic velocity (entrainment factor), and by the phase between the droplet and gas phase oscillations. An experimental set-up was developed to investigate the effect of acoustic oscillations on the motion of individual droplets. In these experiments a droplet produced by a piezo-ceramic droplet generator is allowed to fall through a transparent test section in which an acoustic field has been set up using a pair of acoustic drivers. Images of the droplets in the test section acquired at consecutive instants using a high speed, intensified imaging system were used to determine the time dependent droplet trajectory and velocity. The acoustic velocity was calculated from measured acoustic pressure distributions. The entrainment factor and the phase difference were then determined from these data. The results show how the entrainment factor decreases and the phase difference increases with increasing droplet diameter and frequency, indicating that larger diameters and higher frequencies reduce the “ability” of the droplets to follow the gas phase oscillations. The measured data are in excellent agreement with the prediction of the Hjelmfelt and Mockros model. Both theoretical predictions and measured data were correlated with the Stokes number, which accounts for the effects of droplet diameter and frequency. It was also shown that acoustic oscillations decrease the mean terminal velocity of the droplets.

Effects of acoustic oscillations on flame dynamics of homogeneous propellants in rocket motors

The interactions between acoustic waves and gas-phase flame dynamics of a double-base homogeneous propellant in a rocket motor has been studied by means of a comprehensive numerical analysis. The formulation treats the complete conservation equations of mass, momentum, energy, and species concentration, and accounts for finite rate chemical kinetics in the gas phase and subsurface reactions. The model has been implemented to examine the detailed flow structures and heat-release mechanisms in various parts of the motor, including microscale motions near the propellant surface and macroscale motions in the bulk of the chamber. Results indicate that strong interactions between exothermic reactions and acoustic waves occur in regions with steep temperature gradients due to the large activation energy of the associated chemical kinetics. The dynamic behavior of the luminous flame plays a decisive role in determining the motor stability characteristics. Distributed combustion response in the gas phase provides the energy for driving flow oscillations, and can be treated correctly as a combination of monopole and dipole sources based on acoustic theory.

Pressure‐based method for combustion instability analysis

AbstractAn improved pressure‐based method has been applied to predict the two‐dimensional instability analysis of liquid‐fuelled rocket engines. This method is non‐iterative for transient flow calculations and applicable to all‐speed flows. Validation cases include the shock‐tube problem, the blast flow field and unsteady spraycombusting flows. Computations for the combustion instability analysis were carried out for various combustion parameters such as spray initial conditions and combustor geometries. Unsteady behaviours of the stable and unstable spray flame fields and effects of acoustic oscillations on the fuel droplet vaporization and combustion process are studied in detail. The present numerical model successfully demonstrates the capability of predicting combustion instability as well as fast transient compressible flows at all speeds.

Influence of the Acoustic Oscillations upon Convective Combustion of Aero-Suspensions

Abstract Convective combustion of mono-fuel aero-suspensions in an open-closed channel are treated numerically. The general approach to the problem of the simulation of the dispersed material behaviour to be exploited here is based upon incorporation of multiphase flow equations. The Lax-Wendroff two-step method is used for a solution of two-dimensional planar unsteady problems. The effect of acoustic oscillations caused by combustion upon combustion itself is studied. The different regimes (accelerated and decelerated– of convective combustion spreading are identified and the constitutive criterion of the realization of those regimes is suggested. The computational results to be obtained further are compared with available experimental data.

Muonium acoustic resonance in alpha-quartz

The effect of acoustic oscillations of the α-quartz crystalline lattice on the behaviour of muonium polarization has been studied experimentally. It is shown that when the frequency of the standing ultrasound wave coincides with one of the muonium quadrupole interaction frequencies a specific broadening of the muonium line occurs; that is a muonium acoustic resonance is observed. The possibilities of using this effect for investigating properties of solids by the μSR method are discussed.

Effect of acoustic oscillations on the stability of a plane jet

The problem of the effect of acoustic oscillations on the stability of a compressible ideal-fluid jet flow is examined in the case of a plane jet with standing acoustic waves superimposed across it. The method of dividing the motion into fast and slow with allowance for nonlinear acoustic effects is employed. The acoustic oscillations are found to affect the growth rate of unstable hydrodynamic disturbances.

Parametric x-rays in crystals subjected to the resonant action of ultrasonic waves

The effect of acoustic oscillations on the parametric X-rays is considered. It is predicted that there are two mechanisms of the resonant action of ultrasonic waves on the parametric X-ray radiation leading to a considerable change in the radiation angular density.

Experimental study of laminar-to-turbulent flow transition under the action of acoustic oscillations

Experimental data are given on the effects of acoustic oscillations at frequencies up to 100 kHz on free laminar flow.

Escape of a turbulent jet under the effect of acoustic perturbations

Results are presented of experimental investigations of the local effect of acoustic oscillations of different frequency and constant intensity on the root part of a nonisothermal axisymmetric subsonic turbulent jet escaping from a gas jet atomizer at a different velocity in the S = 0.053–3.84 range of Strouhaille numbers. Data have been obtained indicating the presence of unstable escape modes of a subsonic turbulent jet in an acoustic field; experimental dependences are presented of the relative aperture of the turbulent jet flowing in an acoustic field as a function of various parameters.

Effect of acoustic oscillations on the crystal structure of electrolytic metal deposits: Bondarenko, A.V., Brusnitsina, N.V. Elektrokhimia, Vol 4, No 6 (1968) pp 693–697

Effect of acoustic oscillations on the crystal structure of electrolytic metal deposits: Bondarenko, A.V., Brusnitsina, N.V. Elektrokhimia, Vol 4, No 6 (1968) pp 693–697

Effect of acoustic oscillations on the drying of capillaryporous materials

We present the experimental results which make possible an evaluation of the effect of sound on the processes of internal and external mass transfer.