现代医学手段诱发空蚀的形成及其影响

空泡在随液体流动过程中，当周围压力增加时，空泡体积将急剧缩小或溃灭。由于空泡溃灭过程发生于瞬间，因而在局部将产生极高的瞬时压强，当空泡溃灭发生在固体表面附近时，不断溃灭的空泡所产生的极高压强的反复作用，将破坏固体表面。对生物医学工程中的空泡和空蚀现象的形成、发展和溃灭过程及其危害，空蚀破坏机理及其影响因素，空泡演化过程的数值模拟研究等进行了综合论述，提出了研究空损伤现象需要解决的几个重要问题，为进一步深入研究和应用空化空蚀现象打下基础。     

受控喷丸对水轮机空蚀的作用

水机空馈破坏具有典型的机械疲劳破坏特征,针对其特点,提出采用受控喷丸工艺来减弱水轮机空蚀强度,延缓空蚀的发展,受控喷丸工艺是提高材料表面疲劳强度的有效方法,对水轮机过流部件采用受控喷丸处理,可提高水轮机抗空蚀性能,延长水机过流部件的使用寿命。     

铝熔体中超声辐射杆的空蚀实验及机理研究

超声辐射杆在铝熔体中产生空蚀严重制约其使用寿命及铝熔体的纯净度,针对这一问题,进行了铝熔体钛合金超声辐射杆空蚀试验,采用失重法及熔体Ti元素检测法描述了辐射杆空蚀进程,运用扫描式电子显微镜(SEM)及能谱仪对空蚀试样进行宏/微观形貌观察及成分检测,探讨空蚀各阶段机理.结果表明:辐射杆空蚀以端面为主,随时间推移由端面中心逐渐在横向辐射扩张并在纵向加深;空化孕育期是由于空化泡溃灭冲击辐射杆产生塑变引起的;空化加速期钛合金基体与铝熔体反应生成Al3Ti,该物质硬而脆的特性使钛合金基体在空化冲击作用下脱落是导致失重率快速上升的主要原因;钛合金辐射杆在铝熔体中的空化破坏是由空化泡溃灭冲击及化学腐蚀共同作用导致的.     

内燃机缸套空蚀的原因分析

为延缓与预防内燃机缸套空蚀，对引起内燃机缸套空蚀的原因进行了分析，指出了导致内燃机缸套空蚀的几个主要因素，这对延缓与预防缸套空蚀具有指导意义。     

空蚀诱发相变对金属材料抗空蚀性能的影响

用旋转圆盘试验机研究了4种金属材料的抗空蚀性能。结果表明：亚稳态金属材料Fe-Mn-Si合金，Fe-Cr-Mn-Ni和Fe-Cr-Ni不锈钢空蚀中分别诱发了密排六方晶体结构马氏体和体心立方晶体结构马氏体，其抗空蚀性能依次分别为0C13Ni5Mo的不锈钢的7．3倍，1．8倍和1．6倍；空蚀诱发马氏体相变有助于提高材料的抗空蚀性能，并与空蚀过程中动态相变对应力的响应密切相关；马氏体相变及其逆转变引起的能量耗散和伪弹性大大提高了Fe-Mn-Si合金的抗空蚀性能。     

抗空蚀材料分析

本文通过对空蚀破坏的分析,介绍了当今从软、硬两个方面出发研究的最新抗蚀材料制作方法。特别介绍了离子注入术在水轮机转轮坑蚀中的应用及 IPN 技术。     

船板涂层耐空蚀研究

因舰船船板水下表面蚀损严重,影响了作战寿命及效率,从实际需要及理论探讨,均要求对船板涂层耐空蚀作详细研究,为此,在高速水洞中选择了几种涂层做耐空蚀实验,用麻点率来衡量涂层的耐空蚀能力,选择出了耐空蚀性较好的涂层.     

空化初生的热力学影响研究

人非平衡热力学理论出发，建立了有相变发生时球形气核与围流液体之间能量流和物质流的方程式，在此基础上，确定了自由气核空化初生的条件，燕结合敢泡动力学对此进行了深入的讨论，提出了判断满足空化初生条件的标准。     

不锈钢空蚀磨蚀的形貌特征研究

本文利用转盘、高头水洞、ＳＥＭ、光学金相、ＥＤＡＸ和波谱等研究了奥氏体不锈钢表面发生纯空蚀、纯磨蚀、空蚀磨蚀共存、静水和动水腐蚀的形貌特征以及某些奇特现象；分析对比了黄河水轮机叶片的原体形貌；讨论了空蚀的机制。     

浅谈我处小水电站水轮机空蚀磨损及防护

本文介绍了小水电站水轮机因不同的运行条件、结构参数其空蚀磨损所造成的破坏程度也不相同,本文从实例出发,重点阐述了减少小轮机空蚀磨损的方法。     

初生空化数的计算模型

从“气核惯性失稳导致空化”这一观点出发,提出了应用于数值模拟的初生空化判别标准及其数学模型,采用Ｍｏｎｔｅ－Ｃａｒｌｏ方法模拟空化现象中的各种随机因素,在可靠度的意义下将气核空化初生与流场空化初生联系起来．以黄河小浪底工程消能泄洪洞为例,对三级串联孔板的初生空化数作了计算．     

Affected zone generated around the erosion pit on carbon steel surface at the incipient stage of vibration cavitation

The characteristics of erosion pits on a carbon steel surface were investigated at the incipient stage of cavitation erosion. After a 5-minute experiment performed in an ultrasonic vibration system, needle-like erosion pits appeared on the polished steel surface, and a specially affected zone was formed around the pit. The shape of the pit and the plastic deformation of the affected zone indicate that the me-chanical impaction on the surface is the main reason for the cavitation damage. On the other hand, the iridescent color, the decreased surface hardness and the precipitated carbides on the affected zone prove that the affected zone has experienced a tempering process with the temperature higher than 300℃. The lack of oxygen in the affected zone also proves that it is not a chemical oxygen result. A special phenomenon that a carbon ring forms in the affected zone is explained as a result of the tor- oidal bubbles＇ heating effect at the final stage of the bubble collapse.     

单泡空化振动系统的动力学数值模拟

根据微气泡的动力学方程,用数值计算的方法,采用改进的初始半径对单泡超声空化现象进行了研究。分析表明：气泡的振动对初始半径这个参量很敏感;气泡崩溃速率随气泡初始半径的增加而增大,在一定范围内能保证空化泡稳定的振动,在初始半径为1.6μm处空化程度最强,如果继续增大初始半径则空化程度减弱甚至消失、同时,将分析结果与前人的实验数据比较,发现在考虑液体的可压缩性以后对单泡最佳空化区域有很大的改进。     

超声空化影响因素

在对超声空化的有关理论进行研究的基础上，研究、分析与总结了影响超声空化的液体若干物理参数、声场参数、环境压力等各种因素，为诸如超声空化清洗设备的研究、开发等超声空化技术的实际应用提供有效的帮助。     

空泡溃灭冲击波对流场携带颗粒的作用

讨论了无限大小域中考察液体压缩性影响下空泡溃灭冲击波对固体颗粒的作用，求得了固体颗粒所获得的最大速度，当满足一定条件时，固体颗粒运动速度值之高足以打坏现有水工建筑物所用的混凝土，引起固壁的大面积剥落，形成空蚀，冲击和磨蚀的恶性循环。     

Relationship between the geometric features of carbon steel cavitation erosion debris and the cavitation erosion stages

The debris produced in vibration cavitation tests of three kinds of carbon steel were collected. Their geometric features were analyzed quantitatively and observed respectively by a profilometer and a scanning electronic microscope (SEM) with reference to the investigation of the cavitation damaged surface by SEM and X-ray diffraction (XRD). It was found that among the debris produced in all cavitation erosion stages, more than 45% were platelets because of the occurrence of dislocation and cleavage fracture, and only less than 25% were strands. The number of granule was small in the first cavitation erosion stage and increased rapidly to the number comparable with that of platelets in the next stage, and then reduced in the third stage. The sphericity values of the debris varied in accordance with the stages of cavitation damage, which were 0.3―0.4 in the incubation stage, 0.5―0.7 in the acceleration stage and not less than 0.5 in the maximum rate stage, although a slight decrease occurred in the third stage.     

空化技术理论及应用研究进展

空化技术由于其复杂的流体动力学过程引起的一系列特殊变化,具有特殊的光、力、声等特性,因此研究其机理和应用具有非常重要的意义。从空化理论的产生、数学描述和测量模拟,以及传统和新型应用(机加工、化工、医疗等领域)现状几个方面对空化技术做了回顾和总结,重点对主要的结论和代表性的研究成果做了概括描述,并对其今后的发展做了展望。     

A phenomenological model of mass-exchange between the inside and outside of a cavitation bubble

The mass-exchange between the inside and outside of a cavitation bubble is a complicated process with several kinds of exchange forms acting together, such as gas diffusion, gas-liquid phase transition, chemical reactions and so on. A phenomenological model of mass-exchange was proposed, in which the pressure difference is considered as the drive. Compared with the previous physical models, it has a simpler form and less computational cost. Combining it with Rayleigh-Plesset equation, the equilibrium radius is calculated when the mass-exchange achieves the dynamic balance. The result shows that the equilibrium radius has multiple values. The relationships between the equilibrium radius and the driving ultrasound (pressure amplitude and frequency) are evaluated. We also investigated how these relationships were affected by the model parameters. Finally, the bubble radius evolution in the sulfuric acid driven by different pressures was measured. The experimental result that the equilibrium radius changes with the pressure agrees with the numerical results well. Supported by the National Natural Science Foundation of China (Grant Nos. 10434070, 10704037), the Key Project of Chinese Ministry of Education (Grant No. 103078) and the Young Scholar Technological Innovation Projects of Jiangsu Province (Grant No. BK2007569)     

超声空化泡溃灭冲击波作用固壁面的实验研究

对抛光后的6061铝进行超声振动空蚀实验,发现当超声振动头与材料表面的距离低于1 mm左右材料表面会有明显的空蚀效果。通过实验研究空蚀时间和超声振幅对材料表面粗糙度以及硬度的影响,发现:材料表面粗糙度和硬度先随着空蚀时间的增加而增大;在一定时间后出现平缓过渡期,这是由于材料表面波峰被空化泡溃灭冲击波作用后坍塌所致;继续增加空蚀时间,材料表面粗糙度和硬度会缓慢增大;材料表面粗糙度和硬度随着超声振幅的增大先增大后减小,在超声振幅为10.8μm左右达到最大空蚀效果。     

Effect of roughness and wettability of silicon wafer in cavitation erosion

Material damage of silicon wafer with different roughness and wettability was investigated by using the self-made vibration cavitation apparatus in de-ionized water. Various roughness and wettability of silicon wafer were achieved by changing their morphology and depositing Au, diamond-like carbon films （DLC films） on them. Surface morphology was observed with a scanning electron microscope （SEM） and a surface profilometer, and wettability was characterized by the contact angle measurement. The cavitation erosion results showed that many tiny pits and cracks appeared on the wafer surface as a result of brittle fractures; the number and size of the pits and cracks increased with experiment time, which made material flake away finally; cavitation occurred more easily on the silicon wafer surface with the augment of roughness or contact angle by changing surface morphology or depositing Au, DLC thin film on it, which consequently aggravated cavitation damage.