共查询到18条相似文献,搜索用时 737 毫秒
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为了揭示刚性界面附近气泡空化参数与微射流的相互关系, 从两气泡控制方程出发, 利用镜像原理, 建立了考虑刚性壁面作用的空化泡动力学模型. 数值对比了刚性界面与自由界面下气泡的运动特性, 并分析了气泡初始半径、气泡到固壁面的距离、声压幅值和超声频率对气泡溃灭的影响. 在此基础上, 建立了气泡溃灭速度和微射流的相互关系. 结果表明: 刚性界面对气泡振动主要起到抑制作用; 气泡溃灭的剧烈程度随气泡初始半径和超声频率的增加而降低, 随着气泡到固壁面距离的增加而增加; 声压幅值存在最优值, 固壁面附近的气泡在该最优值下气泡溃灭最为剧烈; 通过研究气泡溃灭速度和微射流的关系发现, 调节气泡溃灭速度可以达到间接控制微射流的目的. 相似文献
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格子Boltzmann方法伪势多相模型具有高效性和复杂几何边界实施的简易性。该文采用改进作用力的伪势多相模型,通过优化参数实现最大程度的热力学一致性,进而提高模型的密度比和稳定性。分别从伪速度、网格不变性、Young-Laplace验证等方面研究了改进模型的性能。通过改进的模型模拟了复杂几何固壁附近空泡溃灭过程。分析了空化泡溃灭阶段的密度场、压力场和速度场演化过程,以及复杂几何固壁附近的空泡动力学特性。结果表明伪势格子Boltzmann方法在探索空泡溃灭和复杂几何固壁间的相互作用规律研究中是一种有效的工具。 相似文献
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为了对双泡耦合的声空化过程进行模拟,本文从流体动力学控制方程和流体体积分数模型出发,在Fluent软件中构建双泡耦合超声空化三维有限元仿真模型,对超声波驱动下流体中双泡耦合声空化动力学过程进行数值模拟,并通过对空化气泡周围声场的变化进行分析研究双泡耦合声空化的非线性动力学特性.结果显示:在超声波驱动下,球形气泡先缓慢扩张,扩张到最大半径后迅速收缩直至溃灭;耦合双气泡间存在相互作用力,使得空化气泡的扩张受到抑制、气泡收缩时间增长;空化气泡在收缩阶段的能量转换能力增强,相比单气泡声空化,耦合双气泡溃灭时气泡内部的压强更大.本文分析结果将为超声空化泡群的动力学过程模拟提供参考. 相似文献
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近壁微气泡溃灭特性的深入研究对靶向给药和基因治疗等技术具有较好的指导作用。该文基于数值模拟技术,采用有限体积法结合流体体积模型对超声作用下的近壁微气泡溃灭特性进行了研究,分析了超声对近壁微气泡溃灭动力学过程的影响。结果表明气泡溃灭最大射流速度与近壁距离无量纲参数在1.1~1.6范围内时成正比,与超声频率在10~60 Hz范围内时成正比,与气泡初始半径在50~100μm范围内时成反比;近壁气泡的二次溃灭最大射流速度大于一次溃灭,二次溃灭的作用更加明显。超声参数对近壁气泡溃灭过程存在较大影响,该研究为超声在医学上的应用提供了依据。 相似文献
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在不同深度条件下的水下构建物超声清洗中,声空化是重要的源动力之一。为探明水下环境压力对声空化的影响,本文基于数值计算的方法,通过对超声波作用下气泡动力学的研究,讨论了环境压力对空化泡溃灭时的气泡最大半径、释放能量以及溃灭功率等因素的影响。结果表明:空化泡最大半径与环境压力在一定范围内呈近似线性关系;随着环境压力增大,空化泡释放能量和溃灭功率均显著减小,且两者在变化趋势和变化幅度上几乎一致;当环境压力大于声压幅值时,空化泡的最大半径、内部压强、内部温度与释放能量均远低于空化发生在环境压力小于声压幅值时的情形。 相似文献
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受限空泡的溃灭是气泡动力学的核心问题,研究表明毫米尺度的空泡溃灭可以拉动附近同尺度的悬浮颗粒运动.本文针对受限空泡溃灭在微尺度下的行为开展研究,通过气泡驱动的球形微马达实验,给出了微气泡溃灭形成射流从而显著推动马达前进的现象,但由于溃灭时间很短,Micro PIV系统不能给出足够的流动细节.进而采用基于流体体积的数值手段模拟了这一过程,获得了流场的时空分布,并通过积分估算了微球获得的冲量,给出了微球所能达到的速度.结果表明这一问题与尺度密切相关,微尺度下空泡溃灭足以推动微球显著运动,在气泡尺寸固定的情况下,微球半径越小,微球与气泡间距离越近,推动的效果越明显.冲量定理则定性地解释了宏观尺度与微尺度下存在差异的原因.这一特殊的微流动问题不但扩展了空化研究的尺度范围,揭示了微尺度下空泡与颗粒作用的特性,而且对提高微马达的驱动效率也具有重要意义. 相似文献
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Cavitation Bubble Collapse near a Curved Wall by the Multiple-Relaxation-Time Shan-Chen Lattice Boltzmann Model 下载免费PDF全文
《中国物理快报》2017,(8)
The cavitation bubble collapse near a cell can cause damage to the cell wall. This effect has received inereasing attention in biomedical supersonics. Based on the lattice Boltzmann method, a multiple-relaxation-time Shan-Chen model is built to study the cavitation bubble collapse. Using this model, the cavitation phenomena induced by density perturbation are simulated to obtain the coexistence densities at certain temperature and to demonstrate the Young-Laplace equation. Then, the cavitation bubble collapse near a curved rigid wall and the consequent high-speed jet towards the wall are simulated. Moreover, the influences of initial pressure difference and bubble-wall distance on the cavitation bubble collapse are investigated. 相似文献
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The thermodynamic of cavitation bubble collapsing is a complex fundamental issue for cavitation application and prevention. The pseudopotential and thermal multi-relaxation-time lattice Boltzmann method (MRT-LBM) is adopted to investigate the thermodynamic of collapsing cavitation bubble in this paper. The simulation results satisfy the maximum temperature equation of the bubble collapse, which derived from the Rayleigh-Plesset (R-P) equation. The validity of thermal MRT-LBM in simulating the collapse process of cavitation bubble is verified. It shows that the temperature evolution of vapor-liquid phase is well captured. Furthermore, the two-dimensional (2D) temperature, velocity and pressure field of the bubble near a solid wall are analyzed. The maximum temperature inside the bubble and wall temperature under different position offset parameters are discussed in details. 相似文献
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A. A. Aganin M. A. Ilgamov L. A. Kosolapova V. G. Malakhov 《Thermophysics and Aeromechanics》2016,23(2):211-220
The cavitation bubble dynamics, the variation of pressure and velocity fields of the surrounding liquid in the process of the bubble axisymmetric compression near a planar solid wall are considered. It is assumed that the liquid is at rest at the initial moment of time, and the bubble has a spheroidal shape. The liquid is assumed inviscid and incompressible, its motion being potential. The bubble surface deformation and the liquid velocity on the surface are computed by the Euler scheme using the boundary element method until the moment of the collision of some parts of the bubble surface with one another. The influence of the distance of the bubble from the wall and its initial nonsphericity on the liquid pressure and velocity fields, the bubble shape, and the pressure inside the bubble at the end of the time interval under consideration are studied. The maximum pressure in liquid is shown to realize at the bottom of the cumulative jet arising at the bubble collapse with direction to the wall. In the upper part of this jet, the velocity and pressure are practically constant, and the pressure in the jet is approximately equal to the pressure in the bubble. 相似文献
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Investigation of cavitation bubble collapse in hydrophobic concave using the pseudopotential multi-relaxation-time lattice Boltzmann method 下载免费PDF全文
《中国物理 B》2021,(4)
The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect.The complexity of this topic is that the cavitation bubble collapse includes many extreme physical phenomena and variability of different solid surface properties.In the present work,the cavitation bubble collapse in hydrophobic concave is studied using the pseudopotential multi-relaxation-time lattice Boltzmann model(MRT-LB).The model is modified by involving the piecewise linear equation of state and improved forcing scheme.The fluid-solid interaction in the model is employed to adjust the wettability of solid surface.Moreover,the validity of the model is verified by comparison with experimental results and grid-independence verification.Finally,the cavitation bubble collapse in a hydrophobic concave is studied by investigating density field,pressure field,collapse time,and jet velocity.The superimposed effect of the surface hydrophobicity and concave geometry is analyzed and explained in the framework of the pseudopotential LBM.The study shows that the hydrophobic concave can enhance cavitation effect by decreasing cavitation threshold,accelerating collapse and increasing jet velocity. 相似文献
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Thermodynamic behaviors and interactions between bubble pairs are important to better understand the cavitation phenomena. In this study, a compressible two-phase model, accounting for thermal effects to investigate the thermodynamic behaviors and interactions between bubble pairs, is developed in OpenFOAM. The volume of fluid (VOF) method is adopted to capture the interface. Validations are performed by comparing the simulation results of a single bubble and bubble pairs with corresponding experimental data. The dynamical behaviors of bubble pairs and their thermodynamic effect at different relative distances γ are investigated and discussed, which help reveal the bubble cloud dynamics. The quantitative analysis of γ effects on the maximum temperature during bubble collapse is performed with three distinct stages identified. For a single bubble collapsing near the rigid surface, the thermodynamic characteristics at different relative distances are similar to that of the bubble pairs, but the maximum temperature is higher since the single bubble can collapse to a smaller volume. 相似文献
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The removal of the adsorbed oil droplet is critical to deoiling treatment of oil-bearing solid waste. Ultrasonic cavitation is regarded as an extremely useful method to assist the oil droplets desorption in the deoiling treatment. In this paper, the effects of cavitation micro-jets on the oil droplets desorption were studied. The adsorbed states of oil droplets in the oil-contaminated sand were investigated using a microscope. Three representative absorbed states of the oil droplets can be summarized as: (1) the individual oil droplet adsorbed on the particle surface (2) the clustered oil droplets adsorbed on the particle surface; (3) the oil droplet adsorbed in a gap between particles. The micro-jet generation during the bubble collapse near a rigid wall under different acoustic pressure amplitudes at an ultrasonic frequency of 20 kHz was investigated numerically. The desorption processes of the oil droplets at the three representative absorbed states under micro-jets were also simulated subsequently. The results showed that the acoustic pressure has a great influence on the velocity of micro-jet, and the initial diameter of cavitation bubbles is significant for the cross-sectional area of micro-jets. The wall jet caused by a micro-jet impacting on the solid wall is the most important factor for the removal of the absorbed oil droplets. The oil droplet is broken by the jet impinging, and then it breaks away from the solid wall due to the shear force generated by the wall jet. In addition to a higher sound pressure, the cavitation bubble at a larger initial diameter is more important for the desorption of the clustered oil droplets. Conversely, the micro-jet generated by the cavitation bubble at a smaller initial diameter (0.1 mm) is more appropriate for the desorption of the oil droplet in a narrow or sharp-angled gap. 相似文献
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Cavitation bubble behavior and bubble–shock wave interaction near a gelatin surface as a study of in vivo bubble dynamics 总被引:1,自引:0,他引:1
The collapse of a single cavitation bubble near a gelatin surface, and the interaction of an air bubble attached to a gelatin surface with a shock wave, were investigated. These events permitted the study of the behavior of in vivo cavitation bubbles and the subsequent tissue damage mechanism during intraocular surgery, intracorporeal and extracorporeal shock wave lithotripsy. Results were obtained with high-speed framing photography. The cavitation bubbles near the gelatin surface did not produce significant liquid jets directed at the surface, and tended to migrate away from it. The period of the motion of a cavitation bubble near the gelatin surface was longer than that of twice the Rayleigh's collapse time for a wide range of relative distance, L/Rmax, excepting for very small L/Rmax values (L was the stand-off distance between the gelatin surface and the laser focus position, and Rmax was the maximum bubble radius). The interaction of an air bubble with a shock wave yielded a liquid jet inside the bubble, penetrating into the gelatin surface. The liquid jet had the potential to damage the gelatin. The results predicted that cavitation-bubble-induced tissue damage was closely related to the oscillatory bubble motion, the subsequent mechanical tissue displacement, and the liquid jet penetration generated by the interaction of the remaining gas bubbles with subsequent shock waves. The characteristic bubble motion and liquid jet formation depended on the tissue's mechanical properties, resulting in different damage mechanisms from those observed on hard materials. 相似文献