Nowak Till, Mettin Robert
Christian Doppler Laboratory for Cavitation and Micro-Erosion, Drittes Physikalisches Institut, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Sep;90(3):033016. doi: 10.1103/PhysRevE.90.033016. Epub 2014 Sep 30.
High-speed recordings reveal peculiar details of the oscillation and translation behavior of cavitation bubbles in the vicinity of an ultrasonic horn tip driven at 20 kHz. In particular, a forward jump during collapse that is due to the rapid reduction of virtual mass is observed. Furthermore, frequently a jetting in the translation direction during the collapse phase is resolved. In spite of strong aspherical deformations and frequent splitting, these bubbles survive the jetting collapse, and they rebound recollecting fragments. Because of incomplete restoration of the spherical shape within the following driving period, higher periodic volume oscillations can occur. This is recognized as a yet unknown source of subharmonic acoustic emission by cavitation bubbles. Numerical modeling can capture the essentials of the unsteady translation.
高速记录揭示了在20kHz驱动的超声变幅杆尖端附近空化泡的振荡和移动行为的奇特细节。特别地，观察到在空化泡溃灭期间由于虚质量的快速减小而产生的向前跳跃。此外，在溃灭阶段经常能分辨出沿移动方向的射流。尽管存在强烈的非球形变形和频繁分裂，这些空化泡在射流溃灭后仍能存活，并通过收集碎片而反弹。由于在随后的驱动周期内球形形状未完全恢复，可能会出现更高阶的周期性体积振荡。这被认为是空化泡产生次谐波声发射的一个尚未知晓的来源。数值模拟能够捕捉非稳态移动的要点。
