Flowfield characteristics of an aerodynamic acoustic levitator

Abstract

A droplet held in a single-axis ultrasonic levitator will principally sustain a certain external blowing along the levitation axis, which introduces the possibility of investigating heat and/or mass transfer from the droplet under conditions which are not too remote from those in spray systems. The focus of the present work is on the influence of the acoustic field on the external flow. More specifically, an axisymmetric submerged gas jet in an axial standing acoustic wave is examined, both in the absence and presence of a liquid droplet. Flow visualization is first presented to illustrate the global flow effects and the operating windows of jet velocities and acoustic powers which are suitable for further study. An analytic and numeric solution, based on the parabolic boundary layer equations are then given for the case of no levitated droplet, providing quantitative estimates of the acoustic field/flow interaction. Detailed velocity measurements using a laser Doppler anemometer verify the analytic results and extend these to the case of a levitated droplet. Some unresolved discrepancy remains in predicting the maximum velocity attainable before the droplet is blown out of the levitator. Two methods are developed to estimate the sound pressure level in the levitator by comparing flowfield patterns with analytic results. These results and observations are used to estimate to what extent acoustic aerodynamic levitators can be used in the future for investigating transport properties of individual droplets.

Stimuli-Responsive Polymers in Nanotechnology: Deposition and Possible Effect on Drug Release

“…(2.1) subjected to the conditions (2.11) and (2.12) (or (2.17) and (2.18)) are solved numerically using the method of straight lines, which was previously successfully applied to kindred problems arising in the theory of single-and multiphase jets and torches described in the boundary layer approximation [18][19][20][21][22][23][24][25].…”

Numerical simulation of oscillating flow field including a droplet

“…The substantial derivative terms in Eqns (2) and (8) are thus defined by (9) where U is the velocity of the computational grid or the oscillating boundary velocity. In order to maintain the level set function as a distance function, reinitialization of the level set function by solving the following equation is proposed [8]: (10) where τ is an artificial time and sign (φ 0 ) indicates the sign of the level set function at the beginning of the reinitialization procedure. The level set function becomes a distance function in the steady-state solution of Eqn (10).…”

“…In order to maintain the level set function as a distance function, reinitialization of the level set function by solving the following equation is proposed [8]: (10) where τ is an artificial time and sign (φ 0 ) indicates the sign of the level set function at the beginning of the reinitialization procedure. The level set function becomes a distance function in the steady-state solution of Eqn (10). The smoothed sign function proposed for numerical treatment of reinitialization [14] is used for Eqn (10); (11) where h is the spatial increment in the finite difference method for solving the governing equations.…”

“…The level set function becomes a distance function in the steady-state solution of Eqn (10). The smoothed sign function proposed for numerical treatment of reinitialization [14] is used for Eqn (10); (11) where h is the spatial increment in the finite difference method for solving the governing equations. A smoothed version of the sign function was also used in [12].…”

“…It is thus important to know the oscillating flow field including a droplet. Streaming flows associated with ultrasonic levitator have been studied experimentally [9,10] and theoretically [11]. Although steady-state flows in and around the droplet were studied, transient flow fields have not yet been discussed well.…”