Nonspherical dynamics and microstreaming of a wall-attached microbubble
Maxime Fauconnier, Cyril Mauger, Jean-Christophe Béra, Claude Inserra
Abstract
Acoustic microstreaming is a nonlinear response of a fluid that undergoes high-amplitude acoustic stimulation and tends to viscously absorb it. The present experimental study investigates the generation of acoustic microstreaming induced by an oscillating wall-attached bubble undergoing nonspherical shape modes. From a microscope top view, the formation of particular flow signatures is explored for the main classes of spherical harmonics $Y_{nm}(\theta, \phi )$ : zonal ( $m = 0 < n$ ), sectoral ( $n = m > 0$ ) and tesseral ( $0 < m < n$ ) oscillation. The microstreaming induced by a bubble animated by a sectoral mode alone reveals a pattern characterized by a $4n$ -lobe flower shape. Tesseral modes give rise to 4 m -lobe flower-shaped patterns. Finally, when sectoral and zonal modes coexist, two kinds of pattern stand out: $2n$ -lobe flower shape and $n$ -pointed star shape. The preferential emergence of one or another streaming pattern is discussed on the basis of the amplitude and phase shift between both shape modes.