Abstract

Development of Acoustic Cavitation Excited by Periodic Sequence of Tone Bursts

V.G.Andreev, G.A.Romanenko, M.A.Burnin (Department of Acoustics, Faculty of Physics, Moscow State University, Moscow, Russia); V.L.Aleynikov (Center of Computer Engineering, Moscow State University, Moscow, Russia)

e-mail: andreev@acs366.phys.msu.su

Development of acoustic cavitation in liquids was studied theoretically and experimentally. Time required for stable cavitation development was evaluated from temporal dependence of noise pressure harmonic components. Acoustic cavitation in water and transformer oil was initiated by vibration of magnetostrictive radiator at 18 kHz. Continuous ultrasound and 0.4-s tone bursts with 4 - 8 s repetition periods were employed for cavitation excitation. A noise pressure distribution was detected by spherical piezoelectric hydrophone with 230 kHz resonance frequency. Hydrophone signal realization of 0.1-s duration was acquired directly after the beginning of radiator vibration. Acquisition of the pressure waveform was performed both in undisturbed liquids and after radiation of several sequences of bursts. A steady state of cavitation was considered to set up after 5 s after beginning of sound radiation in liquids. A procedure of harmonics calculation in 50 T time frame resulted in the temporal dependencies of noise pressure harmonics. It was found that time of steady state cavitation development in undisturbed liquids was about 40-50 ms for our experimental conditions. This time depended on duration, number and repetition rate of applied bursts. In particular, it was reduced more than twice after consequent radiation of 5 . 7 ultrasound bursts with 4-s repetition period. Theoretical approach based on Nolting-Neppiras equation with additional term depending on bubble concentration was employed. Phenomenological model for a temporal dependence of cavitating bubbles in liquids was proposed. It was found that the growth of bubble concentration resulted in significant reduction in maximum radius and time of its collapse.

Section : 4