Nonspherical dynamics and microstreaming of a wall-attached microbubble

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 Ynm(theta,?)Ynm(theta,?): zonal (m=0 < nm=0 < n), sectoral (n=m > 0n=m > 0) and tesseral (0 < m < n0 < m < n) oscillation. The microstreaming induced by a bubble animated by a sectoral mode alone reveals a pattern characterized by a 4n4n-lobe flower shape. Tesseral modes give rise to 4m-lobe flower-shaped patterns. Finally, when sectoral and zonal modes coexist, two kinds of pattern stand out: 2n2n-lobe flower shape and nn-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.

Automated summary

This experimental study investigates the generation of acoustic microstreaming induced by different shape modes, finding that different shape modes result in distinct flow patterns.