Chang Natasha A, Dowling David R
Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.
J Acoust Soc Am. 2009 May;125(5):3088-100. doi: 10.1121/1.3097465.
Acoustic detection and localization of cavitation have inherent advantages over optical techniques because cavitation bubbles are natural sound sources, and acoustic transduction of cavitation sounds does not require optical access to the region of cavitating flow. In particular, near cavitation inception, cavitation bubbles may be visually small and occur infrequently, but may still emit audible sound pulses. In this investigation, direct-path acoustic recordings of cavitation events are made with 16 hydrophones mounted on the periphery of a water tunnel test section containing a low-cavitation-event-rate vortical flow. These recordings are used to localize the events in three dimensions via cross correlations to obtain arrival time differences. Here, bubble localization is hindered by reverberation, background noise, and the fact that both the pulse emission time and waveform are unknown. These hindrances are partially mitigated by a signal-processing scheme that incorporates straight-ray acoustic propagation and Monte-Carlo techniques for compensating ray-path, sound-speed, and hydrophone-location uncertainties. The acoustic localization results are compared to simultaneous optical localization results from dual-camera high-speed digital-video recordings. For 53 bubbles and a peak-signal to noise ratio frequency of 6.7 kHz, the root-mean-square spatial difference between optical and acoustic bubble location results was 1.94 cm. Parametric dependences in acoustic localization performance are also presented.
与光学技术相比，空化的声学检测和定位具有内在优势，因为空化气泡是天然声源，并且空化声音的声学转换不需要对空化流区域进行光学访问。特别是在空化起始附近，空化气泡在视觉上可能很小且出现频率低，但仍可能发出可听声脉冲。在本研究中，利用安装在包含低空化事件率涡流的水洞试验段周边的16个水听器对空化事件进行直接路径声学记录。这些记录用于通过互相关在三维空间中定位事件，以获得到达时间差。在这里，气泡定位受到混响、背景噪声以及脉冲发射时间和波形均未知这一事实的阻碍。一种结合直射线声学传播和蒙特卡罗技术以补偿射线路径、声速和水听器位置不确定性的信号处理方案部分缓解了这些阻碍。将声学定位结果与来自双相机高速数字视频记录的同步光学定位结果进行比较。对于53个气泡和6.7kHz的峰值信噪比频率，光学和声学气泡定位结果之间的均方根空间差异为1.94厘米。还给出了声学定位性能中的参数依赖性。
