Shape and rotation analysis on an ultrasonically levitated droplet using distributed point source method and least square moving particle semi-implicit method

Abstract

Ultrasonic droplet levitation has recently been drawing attention as a way of non-contact transportation. Many experiment revealed that the shape changes or streaming field on the levitating droplets, however, quite small number of numerical simulation have discussed this phenomenon including fluid dynamics within the droplet. In this paper, coupled analysis using the distributed point source method (DPSM) and the least square moving particle semi-implicit (LS-MPS) method, both of which do not require grids or meshes to handle the moving boundary with ease, is suggested. The acoustic radiation force including viscoacoustic torque, which emerges from the viscous boundary layer, is calculated from the distributed point source method result using the idea of boundary layer normal velocity and input to the LS-MPS surface particles. A droplet levitated in an acoustic chamber is simulated using the proposed calculation method. The droplet is vertically supported by a plane standing wave from an ultrasonic driver and subjected to a rotating sound field excited by two acoustic sources on the side wall with different phases. The rotation of the droplet is successfully reproduced numerically and its acceleration is discussed and compared with those in the literature.