Fast acoustic streaming in standing waves : Generation of an additional outer streaming cell

Rayleigh streaming in a cylindrical acoustic standing waveguide is studied both experimentally and numerically for nonlinear Reynolds numbers from 1 to 30. Streaming velocity is measured by means of laser Doppler velocimetry in a cylindrical resonator filled with air at atmospheric pressure at high intensity sound levels. The compressible Navier-Stokes equations are solved numerically with high resolution finite difference schemes. The resonator is excited by shaking it along the axis at imposed frequency. Results of measurements and of numerical calculation are compared with results given in the literature and with each other. As expected, the axial streaming velocity measured and calculated agrees reasonably well with the slow streaming theory for small ReNL but deviates significantly from such predictions for fast streaming (ReNL > 1). Both experimental and numerical results show that when ReNL is increased, the center of the outer streaming cells are pushed toward the acoustic velocity nodes until counter-rotating additional vortices are generated near the acoustic velocity antinodes

Inertial effects on acoustic Rayleigh streaming flow: Transient and established regimes

The effect of inertia on Rayleigh streaming generated inside a cylindrical resonator where a mono-frequency standing wave is imposed, is investigated numerically and experimentally. To this effect, time evolutions of streaming cells in the near wall region and in the resonator core are analyzed. An analogy with the lid-driven cavity in a cylindrical geometry is presented in order to analyze the physical meanings of the characteristic times. Inertial effects on the established streaming flow pattern are then investigated numerically using a code solving the time averaged Navier–Stokes compressible equations, where a mono-frequency acoustic flow field is used to compute the source terms. It is shown that inertia of streaming cannot be considered as the leading phenomenon to explain the mutation of streaming at high acoustic levels

Acoustic and streaming velocity components in a resonant waveguide at high acoustic levels

Rayleigh streaming is a steady flow generated by the interaction between an acoustic wave and a solid wall, generally assumed to be second order in a Mach number expansion. Acoustic streaming is well known in the case of a stationary plane wave at low amplitude: it has a half-wavelength spatial periodicity and the maximum axial streaming velocity is a quadratic function of the acoustic velocity amplitude at antinode. For higher acoustic levels, additional streaming cells have been observed. Results of laser Doppler velocimetry measurements are here compared to direct numerical simulations. The evolution of axial and radial velocity components for both acoustic and streaming velocities is studied from low to high acoustic amplitudes. Two streaming flow regimes are pointed out, the axial streaming dependency on acoustics going from quadratic to linear. The evolution of streaming flow is different for outer cells and for inner cells. Also, the hypothesis of radial streaming velocity being of second order in a Mach number expansion, is not valid at high amplitudes. The change of regime occurs when the radial streaming velocity amplitude becomes larger than the radial acoustic velocity amplitude, high levels being therefore characterized by nonlinear interaction of the different velocity components

Induced flows in acoustic waveguide high level

La propagation d'une onde acoustique en guide est associée, pour de forts niveaux, à un certain nombre de phénomènes de l'acoustique non linéaire. Parmi ces phénomènes, les écoulements redressés (ou vent acoustique), l'effet d'une discontinuité et la transition à la turbulence, à l'étude dans ce mémoire, sont associés à la génération d'écoulements induits. L'étude expérimentale de ces phénomènes repose sur l'adaptation des méthodes de vélocimétrie Laser : Vélocimétrie Laser par effet Doppler (VLD) et Vélocimétrie par Images de Particules (PIV) à la mesure des différents écoulements. Ainsi, des mesures PIV en sortie de convergent, viennent compléter des mesures VLD réalisées antérieurement. Dans l'espoir de mieux appréhender les spécificités de la transition à la turbulence en guide d'onde acoustique, l'évolution de la couche limite de Stokes est étudiée pour des amplitudes de vitesse acoustique croissantes. Une étude expérimentale des écoulements redressés dans un guide d'onde à section carrée est proposée et les spécificités liées à cette géométrie sont recherchées. En outre, l'évolution des tourbillons du vent acoustique en guide d'onde cylindrique est analysée lorsque le vent devient rapide et certains facteurs pouvant être à l'origine de cette évolution sont modifiés. La répartition harmonique dans le guide est ainsi modifiée, puis l'influence des conditions thermiques est abordée en couplant les mesures de vitesses à des mesures de température moyenne dans le guide et en paroi. Une comparaison avec des résultats issus de simulations numériques permet de conforter l'évolution des écoulements redressés observée.High amplitude acoustic propagation in a guide is associated with several non linear phenomena including acoustic streaming, discontinuity effects and transition to turbulence. Those phenomena are studied in this work and are all associated with acoustically induced flows. The present experimental study therefore is based on velocimetry laser techniques: Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV), wich are fitted to the measurement of the different flow velocity components. Firstly, PIV measurements at the exit of a convergent enable to complement previous LDV measurements. Then, in order to a better understanding of the specificity of transition to turbulence in acoustics, the evolution of the Stokes boundary layer is studied for increasing acoustic velocity amplitudes. Then an experimental study of acoustic streaming in a square channel is reported, and the influence of the geometry is examined. Moreover, the evolution of acoustic streaming vortices in a cylindrical waveguide is analyzed for fast streaming and some parameters that could control such evolution are modified. The harmonicdistribution inside the guide is changed and then the influence of thermal conditions is studied by coupling velocity measurements and mean temperature measurements inside the waveguide and along the wall. Some comparisons between measured streaming velocities and numerical simulation results are presented

Transitoire et changement de régime des écoulements redressés de Rayleigh à forts niveaux : Etudes numérique et expérimentale

Acoustic streaming is a second order flow associated with an acoustic wave and generated by the interaction between the wave and a solid wall. In the case of a stationary plane wave at low amplitude i.e. for slow streaming flow, the behaviour of this second order flow is well known: the streaming velocity along the resonator axis is a quadratic function of the acoustic velocity amplitude. For higher acoustic levels i.e. fast streaming flow, a previous numerical study (Inertial effects on non linear acoustic streaming, V. Daru, D. Baltean Carles, C.Weisman, AIP Conf. Proc. 1685, 030003 (2015)) has shown that this streaming velocity becomes a linear function of the acoustic velocity amplitude. In this new flow regime, additional streaming cells has been observed inside the resonator. In the present work, experimental results are presented that confirm the numerical observations. LDV measurements are conducted on a system of different physical dimensions from but similar asymptotic scales as the numerical study. The order of magnitude of streaming velocities on the resonator axis and in the near-wall region are compared for both flow regimes. Transient evolution of streaming velocity for various locations are also analysed for both flow regimes in order to point out the associated characteristic time scales

Numerical and experimental investigation of the role of inertia on acoustic Rayleigh streaming in a standing waveguide

International audienceRayleigh streaming is a mean flow generated by the interaction between a standing wave and a solid wall. In the case of a low amplitude wave inside a cylindrical resonator, the streaming pattern along a quarter wavelength is composed of two toroidal cells: An inner cell close to the tube wall and an outer cell in the core. In the present work the effect of inertia on Rayleigh streaming at high acoustic level is investigated numerically and experimentally. To this effect, time evolutions of streaming cells in the near wall region and in the resonator core are analyzed. For the analysis of the outer cell, an analogy with the lid-driven cavity in a cylindrical geometry is proposed. It is shown that the outer cell is distorted due to convection, but the previously observed emergence of an extra cell cannot be recovered. Inertial effects on the established streaming flow pattern are further investigated numerically by solving time averaged Navier-Stokes equations with an imposed acoustic source. Results are similar to those obtained from the lid-driven cavity simulations. Therefore inertial effects cannot be considered as responsible for the mutation of streaming at high acoustic levels

Étude de l'évolution du vent acoustique non-linéaire par mesures lasers et par simulations numériques directes en guide d'onde stationnaire

L'évolution du vent acoustique en guide d’onde stationnaire avec l'augmentation du nombre de Reynolds non-linéaire est étudiée à partir d’études numérique et expérimentale. La vitesse du vent acoustique est mesurée par Vélocimétrie Laser par effet Doppler (LDV) dans un guide d'onde cylindrique contenant de l'air à pression atmosphérique fermé par un haut-parleur à chaque extrémité. Par ailleurs, une simulation numérique du vent acoustique est effectuée à partir de la résolution des équations de Navier-Stokes compressibles moyennées sur une période. L'excitation acoustique est réalisée par secouage de la cavité selon l'axe à fréquence imposée. Les deux études sont menées dans des configurations asymptotiquement semblables. Les résultats montrent que lorsque le nombre de Reynolds augmente, la composante axiale de la vitesse du vent s'écarte de la prédiction théorique du vent lent. La position des maxima de vitesse est déplacée vers les nœuds de vitesse acoustique et l'amplitude de la vitesse selon l'axe central du guide diminue aboutissant à la formation d'une cellule supplémentaire contra-rotative. La principale différence entre les études numérique et expérimentale est la génération d'harmoniques supérieurs du fait de la propagation non-linéaire, plus importante dans les simulations numériques. Une attention particulière est portée à l'étude de l'influence de ces effets sur le vent acoustique

Fast acoustic streaming in standing waves : Generation of an additional outer streaming cell

International audienceRayleigh streaming in a cylindrical acoustic standing waveguide is studied both experimentally and numerically for nonlinear Reynolds numbers from 1 to 30. Streaming velocity is measured by means of laser Doppler velocimetry in a cylindrical resonator filled with air at atmospheric pressure at high intensity sound levels. The compressible Navier-Stokes equations are solved numerically with high resolution finite difference schemes. The resonator is excited by shaking it along the axis at imposed frequency. Results of measurements and of numerical calculation are compared with results given in the literature and with each other. As expected, the axial streaming velocity measured and calculated agrees reasonably well with the slow streaming theory for small ReNL but deviates significantly from such predictions for fast streaming (ReNL > 1). Both experimental and numerical results show that when ReNL is increased, the center of the outer streaming cells are pushed toward the acoustic velocity nodes until counter-rotating additional vortices are generated near the acoustic velocity antinodes