超声空化与超声医学

随着超声技术应用广泛而迅速的发展,整整一个世纪来,超声空化成了经久不衰的研究课题,特别近１０年来,超声空化成了多种学科的基础研究热点。本扼要地介绍了起声空化的最新研究进展,以及超声空化与超声医学发展的密切关系。     

超声波声孔效应中气泡动力学的研究

在超声快速制取组织细胞病理切片的过程中，发现激励信号对切片制取效果有明显的影响.为了掌握超声激励信号对组织细胞的影响规律，达到快速制取病理切片的最佳状态，从气泡空化模型入手，通过改变激励信号频率、声压、气泡初始半径和液体黏滞系数等参量，研究了声孔效应中气泡动力学激励机制.数值计算表明：空化泡振动随激励声压增强而升高，随液体黏滞系数增强而减弱；一定频率范围内空化泡振动能保持在膨胀、收缩和振荡的稳定空化状态，存在空化泡稳态振动的最佳激励频率；一定初始半径能保证空化泡产生稳定的振动，存在空化泡稳态振动幅度最大的初始半径.实际操作中，在频率、声压、初始半径和黏滞系数综合作用的若干空化阈内，声孔效应使超声快速法制取细胞组织切片获得最佳效果. 关键词： 声孔效应 超声空化 气泡振动 稳态空化域     

关于液体内大规模声处理中空化研究的几点思考——再论声空化工程

再次强调了大规模液体中超声处理、以及为此目的研究声空化的重要性。提出了对这项应用中声空化行为的几点思考,重点是关于声空化的"强度"以及关于电动力式和流体动力式两类产生空化系统所产生空化的不同特性。     

应崇福院士90生辰学术报告会论文关于液体内大规模声处理中空化研究的几点思考——再论声空化工程

再次强调了大规模液体中超声处理、以及为此目的研究声空化的重要性.提出了对这项应用中声空化行为的几点思考,重点是关于声空化的"强度"以及关于电动力式和流体动力式两类产生空化系统所产生空化的不同特性.     

医学超声空化的研究进展

本文介绍了近期医学超声空化研究的若干进展,着重概括了它的研究方法与基本结果,在此基础上提出了一些问题与看法。     

关于表述空化场强弱术语的讨论

声空化是声学中特别是超声学中一个极其重要的物理现象。然而,尽管对于声空化的研究已经有着极长的历史,但仍然有一些极基础的理论问题有待解决。如何来描述或表征声空化状态的强弱程度,就是这样一类的问题。该文对所谓的“空化强度”概念提出质疑,并对影响声空化现象的一些因素做出分析,相应地指出解决问题的一些建议,以期人们对这个无论在理论研究和实际应用方面都有重要意义的问题深入研究。     

超声清洗及其物理机制

本文主要讨论了超声清洗的物理机制：空化、声流、射流及超声振动本身的机械效应．     

液体薄层中的超声空化*

液体薄层中的超声空化,因其边界及所处空间的特殊性,而呈现出非常独特的空化结构和演化行为,在超声清洗、超声钎焊、表面处理、近场声悬浮、超声化学等领域都有所应用。该文梳理了近几年该课题组在液体薄层中的超声空化研究中的一些成果,力图揭示液体薄层内空泡、空化云、空化场的运动和分布规律,及其产生、发展和演化过程,以期对液体薄层中的超声空化行为有一个相对清晰和完整的认识。     

声空化泡对声传播的屏蔽特性*

该文介绍了声空化液体中声波被反常吸收的现象,即驱动声压越大,吸收越强,远场声压越低。研究给出其物理机理是高声压导致强空化,空化泡吸收驱动能量辐射高次谐波,高频声波更易被液体吸收,最终形成更低的远场声压。为了克服空化屏蔽,改善声空化的均匀性,提出了改变工作液体的空化阈值的思路。并就简单的双层液体系统进行了计算和实验,结果证实这种思路的正确性。     

医学超声中的超声空化

本文全面地介绍了医学超声与超声空化的关系,综述了医学超声各个应用领域中有关超声空化的最新研究进展,讨论了超声空化在医学超声中的作用及研究超声空化对发展医学超声的重要意义.     

超声清洗装置空化噪声谱分析法空化噪声级测量

空化强度是用以衡量液体介质中空化活动的剧烈程度,同时空化效应在超声清洗中起关键作用,因此,测量超声清洗槽中的空化强度便可了解其中空化活动的情况.当发生空化时,液体介质中会产生成分复杂空化噪声,对空化噪声谱进行分析和计算得到空化噪声级,据此可判断空化强度.实验测得结果表明:超声清洗装置内稳态空化分布广泛、均匀,瞬态空化分...     

Cavitation characteristics analysis of a novel rotor-radial groove hydrodynamic cavitation reactor

Hydrodynamic cavitation was widely used in sterilization, emulsion preparation and other industrial fields. Cavitation intensity is the key performance index of hydrodynamic cavitation reactor. In this study, a novel rotor-radial groove (RRG) hydrodynamic cavitation reactor was proposed with good cavitation intensity and energy utilization. The cavitation performances of RRG hydrodynamic cavitation reactor was analyzed by utilizing computational fluid dynamics method. The cavitation intensity and the cavitation energy efficiency were used as evaluation indicators for RRG hydrodynamic cavitation reactor with different internal structures. The amount of generated cavitation for various shapes of the CGU, interaction distances and rotor speed were analyzed. The evolution cycle of cavitation morphology is periodicity (0.46 ms) in the CGU of RRG hydrodynamic cavitation reactor. The main cavitation regions of CGU were the outflow and inflow separation zones. The cavitation performance of rectangular-shaped CGU was better than the cylindrical-shaped CGU. In addition, the cavitation performance could be improved more effectively by increasing the rotor speed and decreasing the interaction distance. The research results could provide theoretical support for the research of cavitation mechanism of cavitation equipment.     

Numerical prediction of tip vortex cavitation behavior and noise considering nuclei size and distribution

The tip vortex cavitation behavior and sound generation were numerically analyzed. A numerical scheme combining Eulerian flow field computation and Lagrangian particle trace approach was applied to simulate tip vortex cavitation. Flow field was computed by using hybrid method which combines Reynolds-Averaged Navier-Stokes solver with Dissipation Vortex Model. The trajectory and behavior of each cavitation bubble were computed by Newton’s second law and Rayleigh-Plesset equation, respectively. According to nuclei population data, the cavitation nuclei were distributed and convected into the tip vortex flow. Calculated volume of the cavitation bubble and the trajectory were used as the input of cavitation bubble noise analysis. The relationship of cavitation inception, sound pressure level, and cavitation nuclei size was studied at several cavitation numbers. It was found that cavitation inception of smaller nuclei is more sensitive to the change of cavitation number and cavitation noise due to the cavitated smallest nuclei has the most influence on overall tip vortex cavitation noise.     

Mechanism and dynamics of hydrodynamic-acoustic cavitation (HAC)

Bubble clusters in hydrodynamic cavitation, acoustic cavitation and hydrodynamic-acoustic cavitation (HAC) are investigated via high-speed photography. By introducing a cavitation state variable, a method for cavitation characterization is proposed. The periodic characteristics and intensity distributions of hydrodynamic cavitation, acoustic cavitation and HAC are quantitatively analyzed using this method. It is found that the range of HAC is evidently widened and the strength of HAC is significantly enhanced compared with hydrodynamic cavitation or acoustic cavitation. Furthermore, we developed a preliminary physical model describing the dynamics of a cavitation bubble in HAC and proposed a mechanism to explain the enhancement of the intensity in HAC.     

Study of low-frequency ultrasonic cavitation fields based on spectral analysis technique

A kind of new spectral analysis method for analyzing ultrasonic cavitation fields is brought forward in this paper. This method extracts the line spectrum and the continuous spectrum from the cavitation noise spectrum respectively, then obtains estimations of the energy intensities of different cavitation components such as the stable cavitation and the transient cavitation through corresponding calculations. The method is also applied to investigate low-frequency ultrasonic cavitation fields and is compared with spectral level analysis method. The results show that this method can provide adequate information on the course of the cavitation process, give the delicate analysis on the transient cavitation and the stable cavitation, and help to gain an insight into the nonlinear process of cavitation fields. Moreover, it also shows that the criterion for characterization of cavitation intensity presented by Frohly through studying the high-frequency ultrasonic fields can be used to evaluate the low-frequency ultrasonic fields.     

Experimental research into time–frequency characteristics of cavitation noise using wavelet scalogram

The cavitation has become the main cause of the damage to the hydraulic machine. Cavitation detection is very important to guarantee the safe running of the hydraulic machine. The sound, especially the audible sound, based methods are becoming attractive due to their simplicity and logicality in the application. However, the cavitation noise is easy to be contaminated by the background noise. In order to understand the characteristics of the cavitation noise deeply, using the wavelet scalogram analysis, this paper presents an experimental study to investigate the time–frequency characteristics of the cavitation noise of various cavitation states and the relation between the cavitation noise and the cavitation process. In addition, the method of parameters optimization for the wavelet is used to improve the transform performance of the wavelet scalogram. The results show that: the cavitation noise is composed of the components with wide band frequency and obvious impulse feature; but the cavitation noise of different cavitation stages has different time–frequency characteristics and compositions; in addition, the cavitation noise can be distinguished from the background noise because they have totally different frequency characteristic. This study validates that the cavitation noise can be used to detect the cavitation state and monitor the cavitation process.     

Acoustic characterization of cavitation intensity: A review

Cavitation intensity is used to describe the activity of cavitation, and several methods are developed to identify the intensity of cavitation. This work aimed to provide an overview and discussion of the several existing characterization methods for cavitation intensity, three acoustic approaches for charactering cavitation were discussed in detail. It was showed that cavitation noise spectrum is too complex and there are some differences and disputes on the characterization of cavitation intensity by cavitation noise. In this review, we recommended a total cavitation noise intensity estimated via the integration of real cavitation noise spectrum over full frequency domain instead of artificially adding inaccurate filtering processing.     

高速水流中旋涡空化所引起的空蚀和振动

为了研究旋涡空化所引起的空蚀和振动观象以及二者的关系,采用高速摄影的方法,观察了发生在射流放水阀山部的空化形态。采用快速富里叶变换（FFT）分析了空化所引起的振动。采用失重法,进行了空蚀实验。结果表明,旋涡空化能引起严重的空蚀和剧烈的振动。在旋涡空化发展的个同阶段,其所导致的振动和空蚀呈观了个同的特性。当Sσ>0.74时,随空化数的变化,振动和空蚀呈现了相同的变化趋势,但是,在0.50<σ<0.74的范围内,振动和空蚀呈现了相反的变化趋势。这是由于水流中空化旋涡的数目和形态随空化数的变化,以及旋涡空化引起振动和空蚀的机理不同所造成的。     

正则系综条件下空化空泡形成的分子动力学模拟

液体中空化现象的研究对减少空蚀破坏, 提高空化空泡的有效利用具有重要意义.本文采用分子动力学模拟的方法, 对正则系综条件下系统中空化的发生特性进行研究, 分析空化发生的机理, 讨论温度、数密度等因素对空化发生的影响, 并与格子Boltzmann方法进行了比较.模拟结果表明: 温度和数密度的变化, 都对系统中的空化产生显著影响.其中, 温度升高, 使系统中空化空泡的形成由稳定变得不稳定, 最终难以形成.数密度降低, 则会促进空化空泡的形成.随着数密度的减小, 温度对空化空泡形成的影响程度下降.     

绕空化器自然空化与通气空化的对比

本文采用高速全流场显示技术和动态应变式测力系统相结合对比了绕圆盘空化器自然空化流场与通气空化流场流动结构和影响因素。结果表明,自然空化和通气空化在流场形态上有着相同的发展过程:初生空化、带状空化、团状空化、半透明超空化和透明超空化;空化数是自然空化主要影响因素之一,通气量是通气空化主要影响因素之一。通气能够促进绕空化器空化流动发展程度。