论述了一种新型的微泵原理,该微泵将激光聚焦于管道内液体介质产生空化泡,利用空化泡生长和溃灭过程中产生的流体推进速度和推进力驱动流体运动。采用Volume Of Fluid方法模拟了管道内空化泡的动力学特性,计算了不同管径对管道内空化泡...论述了一种新型的微泵原理,该微泵将激光聚焦于管道内液体介质产生空化泡,利用空化泡生长和溃灭过程中产生的流体推进速度和推进力驱动流体运动。采用Volume Of Fluid方法模拟了管道内空化泡的动力学特性,计算了不同管径对管道内空化泡动力学特性的影响。研究结果表明:管道内空化泡在生长和溃灭过程中所产生的流速可以高速推动流体运动,随着管道的管径越小,管道内空化泡的第一次脉动周期越长,空化泡越稳定;同时,管道内空化泡生长和溃灭过程中附近流体的流速也随着管径减小而呈现增大的趋势。展开更多
采用直接模拟方法,研究气泡在浮力作用下的变形机理及气泡尾部驻涡形成机理。用二阶时空精度的变密度投影方法解Navier-Stokes方程,用VOF(volume of fluid)方法捕捉界面。获得了气泡平衡时的上升速度,并探讨气泡内部环流和气泡尾部驻涡...采用直接模拟方法,研究气泡在浮力作用下的变形机理及气泡尾部驻涡形成机理。用二阶时空精度的变密度投影方法解Navier-Stokes方程,用VOF(volume of fluid)方法捕捉界面。获得了气泡平衡时的上升速度,并探讨气泡内部环流和气泡尾部驻涡间的关系。展开更多
采用NGFM(New version of Ghost Fluid Method)处理复杂计算域的固壁边界,用RGFM(Real Ghost Fluid Method)求解气-水界面附近网格节点的状态参数,从而在直角坐标系下对复杂计算域的水下高压气泡膨胀问题进行数值模拟。流场控制方程选用...采用NGFM(New version of Ghost Fluid Method)处理复杂计算域的固壁边界,用RGFM(Real Ghost Fluid Method)求解气-水界面附近网格节点的状态参数,从而在直角坐标系下对复杂计算域的水下高压气泡膨胀问题进行数值模拟。流场控制方程选用Euler方程,用五阶WENO格式离散空间导数项,二阶Runge-Kutta法离散时间导数项;气-水界面追踪使用Level Set方法,对Level Set方程,用五阶HJ-WENO(Hamilton-Jacobi WENO)和三阶Runge-Kutta法求解。将计算结果与任意坐标系下的结果进行对比,验证了NGFM在笛卡尔网格中处理复杂形状固壁边界的可行性。得到了水下流场压力等值线图、高压气泡的演变过程以及特定点处的压力-时间曲线。计算结果表明,高压气泡在固壁反射激波的作用下,膨胀过程受到抑制;强激波在固壁的反射会导致固壁附近出现大范围的空化流动。展开更多
In this study we characterized and investigated the specific phenomenon of "companion drops" in the drop-ondemand(DOD) ink jetting process.A series of simulations based on a piezoelectric DOD printhead syste...In this study we characterized and investigated the specific phenomenon of "companion drops" in the drop-ondemand(DOD) ink jetting process.A series of simulations based on a piezoelectric DOD printhead system is presented,adapting the volume-of-fluid(VOF) interface-capturing method to track the boundary evolution and model the interfacial physics.The results illustrate the causality between the generation of companion drops and droplet deviation behavior,as well as their close correlations with ink jetting straightness and printing accuracy.The characteristics of companion drops are summarized and compared with those of satellite drops.Also,a theoretical mechanism for the generation of companion drops is presented,and their effects and behaviors are analyzed and discussed.Finally,the effects of critical factors on the generation of companion drops are investigated and characterized based on variations in the printable pressure range.Recommendations are given for the suppression of companion drops and for the improvement of printing accuracy.展开更多
文摘论述了一种新型的微泵原理,该微泵将激光聚焦于管道内液体介质产生空化泡,利用空化泡生长和溃灭过程中产生的流体推进速度和推进力驱动流体运动。采用Volume Of Fluid方法模拟了管道内空化泡的动力学特性,计算了不同管径对管道内空化泡动力学特性的影响。研究结果表明:管道内空化泡在生长和溃灭过程中所产生的流速可以高速推动流体运动,随着管道的管径越小,管道内空化泡的第一次脉动周期越长,空化泡越稳定;同时,管道内空化泡生长和溃灭过程中附近流体的流速也随着管径减小而呈现增大的趋势。
文摘研究了耦合Level Set(LS)方法处理介质界面算法,通过对比旋转流场和剪切流场下的界面捕捉情况,给出了各种不同方法在处理介质界面过程中的优缺点,分析了产生这种现象的原因。通过对比分析得到,耦合粒子Level Set(Particle Level Set,PLS)方法以及耦合Level Set和VOF(Coupled Level Set and Volume of Fluid,CLSVOF)方法相比于单纯的LS方法,在流体守恒性质方面有很大的提高,PLS方法可以根据撒播粒子和精确追踪示踪粒子修正LS界面;而CLSVOF方法可以通过重构界面和体积输运,重新初始化LS函数。在实际物理应用中,PLS方法多次重新撒播示踪粒子会降低界面精度,且对每个示踪粒子的追踪需要加大CPU内存,而CLSVOF方法更加高效和合理。
基金Project supported by the National Key Technology R&D Program(No. 2011BAD01B03)the Key Project of Science and Technology Program of Zhejiang Province (No. 2009C11099)the Zhejiang Provincial Natural Science Foundation (No. Y1110230)
文摘In this study we characterized and investigated the specific phenomenon of "companion drops" in the drop-ondemand(DOD) ink jetting process.A series of simulations based on a piezoelectric DOD printhead system is presented,adapting the volume-of-fluid(VOF) interface-capturing method to track the boundary evolution and model the interfacial physics.The results illustrate the causality between the generation of companion drops and droplet deviation behavior,as well as their close correlations with ink jetting straightness and printing accuracy.The characteristics of companion drops are summarized and compared with those of satellite drops.Also,a theoretical mechanism for the generation of companion drops is presented,and their effects and behaviors are analyzed and discussed.Finally,the effects of critical factors on the generation of companion drops are investigated and characterized based on variations in the printable pressure range.Recommendations are given for the suppression of companion drops and for the improvement of printing accuracy.
