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.
Standard and inverse transducer-plane streaming patterns in resonant acoustofluidic devices: Experiments and simulations
Abstract In this paper, we report a new transducer-plane streaming pattern, which we call here inverse four-quadrant transducer-plane streaming, in an ultrasound-excited thin-layer glass capillary device, illustrate the importance of the travelling wave component and emphasize its phase difference with the standing wave component of three-dimensional acoustic fields excited in thin-layer resonant acoustofluidic particle manipulation devices on the formation of transducer-plane streaming patterns through numerical simulations. A mathematical model was created for solving the three-dimensional acoustic streaming fields from limiting velocities derived from predefined acoustic fields, capturing both the standing wave and travelling wave components and their phase relations. This model was then successfully applied to interpret the unusually reversed in-plane streaming patterns seen in a silicon-based fluid channel. It was found that, by tuning the phase difference between the standing and travelling wave components, φ, the transducer-plane streaming vortices could be shifted along the fluid channel and reversed streaming patterns can be excited when φ differ by π, which could provide insights for the control of transducer-plane streaming in thin-layer acoustofluidic devices and may have promising potential for acoustofluidic applications such as nanoscale particle manipulation.
The chromosomes of Chrysanthemum,
NEW varieties of the garden chrysanthemum arise primarily from seed. They are propagated vegetatively and many give rise to bud sports in sequence and in parallel to give whole families of varieties. The original sports would naturally be chimras and it is not surprising therefore that they often revert to the previous type. Whereas some varieties sport continually from the time of their origin, others remain stable for many years. Those considered in this account do, mostly, sport freely. Since varieties may remain stable for a considerable number of years and then suddenly sport it is probable that all varieties possess the ability to sport. The origin of bud sports is unpredictable. Some confusion in naming has arisen as the same or similar sports have occurred and been propagated in different places under different names. Consequently there are, for example, several forms similar to, but not identical with, the original Favourite Supreme raised by Messrs A. G. Vinten. It might well be that each individual variety would be better termed a sub-family to include all its minor variants. The different Chrysanthemum sports are described in scattered numbers of the R.H.S. Journal—more particularly, for the Favourite family, in Vol. 63, 1938, pp. 139-141. The object of this study is to discover the cause of sporting.