Abstract

Bimodal Bubble Cluster as a Result of Bubble Fragmentation in a Bipolar Acoustic Pulse

D.V.Voronin, G.N.Sankin, V.S.Teslenko (Lavrentyev Institute of Hydrodynamics, Novosibirsk, Russia); R.Mettin, W.Lauterborn (Drittes Physikalisches Institut, Universitat Gottingen, Gottingen, Germany)

e-mail: voron@hydro.nsc.ru

The dynamics of bubbles fragmentation is experimentally and computationally investigated for a bipolar acoustic pulse (~10 MPa, 2 us, the interval between rarefaction and compression waves is variable), passing through a liquid with gaseous bubbles (R0~0,1-0,5 mm). Irregular bubble pulsation results in subsequent bubble fragmentation, which produces micro-bubbles. At the moment of the jet fragmentation near to a neck between bubble and the fragment small spots with high local pressure and temperature appear. When the rarefaction wave of the initially bipolar impulse passes, the bubbles generate a secondary shock wave, which may be quite strong under certain conditions. This secondary compression wave influences the bubble fragments, which collapse and rebound in the pressure radiation field of the larger bubbles. In the paper the process is numerically investigated in detail and experimentally tested. The cavitation processes in the liquid have been generated experimentally with the help of an electromagnetic generator of acoustic shock waves. The modelling has been performed within the frame of a two-dimensional axisymmetric non-stationary approach on the base of conservation laws for the model of an ideal compressible liquid. The thermodynamic flow field has been computed both in the liquid and in the bubble. Thus the formation and dynamics of a bimodal bubble cluster is observed.

Section : 4