1、Experimental investigations on the collapse of cavity cluster in high power ultrasound fieldsLixin Bai , Weilin Xu , Yichi Zhang , Yanfu Li , Defa HuangSichuan UniversityChengdu, ChinaLixin.bai1Sichuan University Bai Lixin IntroductionMotivationCloud cavitationBackgroundNoltingk, Neppiras and Flynn

2、et al.Mrch, Wang and Brennen et al.Brennen, 20072Sichuan University Bai Lixin Objective of the paperExperiments with cavity cluster in high power ultrasound fieldshigh speed photographic observationsflow field measurements (PIV)Expected Resultsbetter understanding of the collapse of cavity clusterex

3、perimental evidence that cavity cluster collapse towards the centera physical phenomena which may be responsible for the propagation of shock wave in the cavity cluster3Sichuan University Bai Lixin ExperimentExperimental arrangement for investigation of cavity cluster4Sichuan University Bai Lixin AB

4、C DUltrasonic hornGlass flat plate(1)(2)1 mmFig.3. Cavity cluster between an ultrasonic horn and a flat plate. (1) A high-speed photograph (Photron Fastcam high-speed camera, exposure time 1 s). (2) Velocity field in the dotted line area.5Sichuan University Bai Lixin ExplanationsLauterborn and Hents

5、chel investigated the motion of cavitation bubbles in ultrasonic field by photography and found that the cavitation bubbles have a tendency to accumulate at pressure antinodes when they are sufficiently small. The primary Bjerknes force may be responsible for the motion of bubbles towards the center

6、 of cavity cluster.Chahine and Duraiswami showed that the bubbles on the outer edge of cavity cluster will tend to collapse asymmetrically and develop jets directed toward the center of the cloud. Small bubbles produced during the collapse many move with the jets, which may also be responsible for t

7、he motion of bubbles towards the center of cavity cluster.7Sichuan University Bai Lixin ExplanationsLauterborn and Hentschel investigated the motion of cavitation bubbles in ultrasonic field by photography and found that the cavitation bubbles have a tendency to accumulate at pressure antinodes when

8、 they are sufficiently small. The primary Bjerknes force may be responsible for the motion of bubbles towards the center of cavity cluster.Chahine and Duraiswami showed that the bubbles on the outer edge of cavity cluster will tend to collapse asymmetrically and develop jets directed toward the cent

9、er of the cloud. Small bubbles produced during the collapse many move with the jets, which may also be responsible for the motion of bubbles towards the center of cavity cluster.8Sichuan University Bai Lixin 12345678910abcdefghijklmnopqrstuvwxyz0.4 mmThe growth and collapse of cavitation bubbles in

10、two acoustic cycles (Photron Fastcam high-speed camera, framing rate 100000 fps, exposure time 370 ns).10Sichuan University Bai Lixin Variation of the diameters of the cavitation bubbles in Fig.5 with time in two acoustic cycles.11Sichuan University Bai Lixin ConclusionThe growth and collapse of cav

11、ity cluster in 20 kHz ultrasonic fields were investigated by high-speed photography. The motion of cavitation bubbles was strongly influenced by the acoustic streaming. Bubbles moved from the perisphere downward towards the cone tip in the axis under the ultrasonic horn and then moved downward along

12、 the axial direction. However, bubbles were found stray from the acoustic streaming upwards towards the center of the cavity cluster when the cavitation bubbles collapse. The primary Bjerknes force and jets directed toward the center of the cloud produced during the bubbles collapse may be responsible for the motion of bubbles towards the center of cavity cluster. The growth and collapse of cavitation bubbles which emerged at the same time in the same cavity cluster were recorded at 100000 fps. The relative large cavitation bubbles will growth and collapse with relative hi