The coupled level-set and volume of fluid(CLSVOF)method is an advanced interface-capturing method that has been extended to handle overset grid systems.However,artificial uneven interface may be observed across block ...The coupled level-set and volume of fluid(CLSVOF)method is an advanced interface-capturing method that has been extended to handle overset grid systems.However,artificial uneven interface may be observed across block boundaries of different sizes and geometries.We present an improved inter-grid VOF interpolation and mass correction scheme to address the issue.To demonstrate the capability of the improved CLSVOF method,it is applied to the simulation of a container ship in pitch and heave motions under both head sea and following sea irregular wave conditions.Our simulation proves that the improved CLSVOF method is capable of revealing detailed physics difficult to see with other methods.Those phenomena simulated in our work include the extensive greenwater propagation on the ship deck,the breakup of overtopping waves into small droplets,and the formation and collapse of air pockets in sudden bow and stern slamming which cause strong and highly localized impacts on the ship bow,stern,and rudder.展开更多
本文利用CLSVOF-IB方法研究海洋管道所受的流体作用力及其涡激振动特性,其中CLSVOF(Coupled Level-Set and VOF)方法用来模拟海洋自由波面,浸入边界(immersed boundary,IB)方法用于模拟海洋管道与流体之间的相互作用力。计算结果表明,CL...本文利用CLSVOF-IB方法研究海洋管道所受的流体作用力及其涡激振动特性,其中CLSVOF(Coupled Level-Set and VOF)方法用来模拟海洋自由波面,浸入边界(immersed boundary,IB)方法用于模拟海洋管道与流体之间的相互作用力。计算结果表明,CLSVOF-IB方法能够准确分析海洋立管的流固耦合特性,可通过选择合适的管道直径和来流速度来解决管道的流致振动问题。此外通过改变流体傅汝德数(Fr数),结果还表明该数值方法能较好捕捉海洋管道与海洋自由波面的相互作用过程。展开更多
为了考察液滴的撞击对液膜变形行为的影响规律,利用CLSVOF(coupled level set and volume of fluid)方法模拟双液滴同时撞击平面液膜后的流动过程,获得了不同水平间隔距离、不同撞击速度的两液滴撞击平面液膜后的演变过程特点,通过分析...为了考察液滴的撞击对液膜变形行为的影响规律,利用CLSVOF(coupled level set and volume of fluid)方法模拟双液滴同时撞击平面液膜后的流动过程,获得了不同水平间隔距离、不同撞击速度的两液滴撞击平面液膜后的演变过程特点,通过分析不同时刻压力场分布,探索了两液滴水平间隔距离、韦伯数和撞击速度对双液滴同时撞击液膜后流动过程、形态及对水花高度和中心射流高度的影响。结果表明,碰撞速度较大时的中心液膜射流高度大于碰撞速度较小时的;We数较大时中心射流顶端将产生二次液滴;液滴间距对撞击后初始时(3 ms之前)撞击点两侧的开始水花高度没有明显影响。展开更多
A splashing crown is commonly observed when a high-speed drop impacts a liquid film. The influence of the liquid viscosity on the crown＇s evolution is not yet clear. We review several existing theories of this proble...A splashing crown is commonly observed when a high-speed drop impacts a liquid film. The influence of the liquid viscosity on the crown＇s evolution is not yet clear. We review several existing theories of this problem, and carry out a series of numerical simulations. We find that a three-segment model can describe the crown＇s motion. In the very early stage when the crown is barely visible, the influence of viscosity is small. Later, a shallow water approach used in most existing models is applicable as long as the initial conditions are formulated properly. They depend on viscous dissipation in the intermediate period. Preliminary estimation based on a dissipation function is proposed to characterize the influence of viscosity in this problem.展开更多
The interactions between the bubbles and the particles near structures are important issues for the applications of the cavitation in the fluid machinery.To study the hidden microscopic mechanisms,a numerical method f...The interactions between the bubbles and the particles near structures are important issues for the applications of the cavitation in the fluid machinery.To study the hidden microscopic mechanisms,a numerical method for simulating the laser-generated bubble between the solid wall and a particle is developed in this paper with considerations of the viscosities and the compressibility of the gas and the liquid phases,as well as the surface tension between them.The gas-liquid interface is tracked by the coupling level set and the volume of fluid(CLSVOF)method.The numerical results clearly reveal that the particle can influence the cavitation bubble behaviors.The potential damage of the nearby structures is numerically quantified in terms of the wall pressure,which helps better understand the synergetic effects of the particle on the cavitation.The effects of three dimensionless parameters on the wall pressure are also investigated,especially,on the peak pressure,namely,γ1(defined as L_(1)/R_(max),where L_(1)is the distance from the center of the initial bubble to the solid wall and R_(max)is the maximum bubble radius),γ_(2)(defined as L_(2)/R_(max),where L_(2)is the distance from the lower surface of the spherical particle to the initial bubble center)andθ(defined as Rp/R_(max),where Rp is the spherical particle radius).Further numerical results show that these parameters play a dominant role in determining the peak pressure.When y_(1)<1.00,the peak pressure on the solid wall during the bubble collapse is mainly resulted from the liquid jet.Whenγ1>1.00,the peak pressure is caused by the shock wave.With the increase ofθor decrease ofγ_(2),the peak pressure increases.Whenγ_(2)>2.00,the effect of the particle on the bubble behavior can be neglected.展开更多
The Large Eddy Simulation （LES） of the wave breaking over a muddy seabed is carried out with a Coupled Level Set and Volume Of Fluid （CLSVOF） method to capture the interfaces.The effects of the mud on the wave bre...The Large Eddy Simulation （LES） of the wave breaking over a muddy seabed is carried out with a Coupled Level Set and Volume Of Fluid （CLSVOF） method to capture the interfaces.The effects of the mud on the wave breaking are studied.The existence of a mud layer beneath an otherwise rigid bottom is found to have a similar effect as an increase of the water depth.As compared with the case of a simple rigid bottom,the inception of the wave breaking is evidently delayed and the breaking intensity is much reduced.The dissipation of the wave energy is shown to have very different rates before,during and after the breaking.Before and after the breaking,the mud plays an important role.During the breaking,however,the turbulence as well as the entrainment of the air also dissipate a large amount of energy.展开更多
基金This work was supported by the Ocean Systems Simulation and Control Laboratory(OSSCL)Consortium.
文摘The coupled level-set and volume of fluid(CLSVOF)method is an advanced interface-capturing method that has been extended to handle overset grid systems.However,artificial uneven interface may be observed across block boundaries of different sizes and geometries.We present an improved inter-grid VOF interpolation and mass correction scheme to address the issue.To demonstrate the capability of the improved CLSVOF method,it is applied to the simulation of a container ship in pitch and heave motions under both head sea and following sea irregular wave conditions.Our simulation proves that the improved CLSVOF method is capable of revealing detailed physics difficult to see with other methods.Those phenomena simulated in our work include the extensive greenwater propagation on the ship deck,the breakup of overtopping waves into small droplets,and the formation and collapse of air pockets in sudden bow and stern slamming which cause strong and highly localized impacts on the ship bow,stern,and rudder.
文摘本文利用CLSVOF-IB方法研究海洋管道所受的流体作用力及其涡激振动特性,其中CLSVOF(Coupled Level-Set and VOF)方法用来模拟海洋自由波面,浸入边界(immersed boundary,IB)方法用于模拟海洋管道与流体之间的相互作用力。计算结果表明,CLSVOF-IB方法能够准确分析海洋立管的流固耦合特性,可通过选择合适的管道直径和来流速度来解决管道的流致振动问题。此外通过改变流体傅汝德数(Fr数),结果还表明该数值方法能较好捕捉海洋管道与海洋自由波面的相互作用过程。
文摘为了考察液滴的撞击对液膜变形行为的影响规律,利用CLSVOF(coupled level set and volume of fluid)方法模拟双液滴同时撞击平面液膜后的流动过程,获得了不同水平间隔距离、不同撞击速度的两液滴撞击平面液膜后的演变过程特点,通过分析不同时刻压力场分布,探索了两液滴水平间隔距离、韦伯数和撞击速度对双液滴同时撞击液膜后流动过程、形态及对水花高度和中心射流高度的影响。结果表明,碰撞速度较大时的中心液膜射流高度大于碰撞速度较小时的;We数较大时中心射流顶端将产生二次液滴;液滴间距对撞击后初始时(3 ms之前)撞击点两侧的开始水花高度没有明显影响。
基金Project supported by the National Natural Science Foundation of China(Nos.11672310 and 11372326)the National Basic Research Program of China(No.2014CB04680202)
文摘A splashing crown is commonly observed when a high-speed drop impacts a liquid film. The influence of the liquid viscosity on the crown＇s evolution is not yet clear. We review several existing theories of this problem, and carry out a series of numerical simulations. We find that a three-segment model can describe the crown＇s motion. In the very early stage when the crown is barely visible, the influence of viscosity is small. Later, a shallow water approach used in most existing models is applicable as long as the initial conditions are formulated properly. They depend on viscous dissipation in the intermediate period. Preliminary estimation based on a dissipation function is proposed to characterize the influence of viscosity in this problem.
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the National Natural Scicncc Foundation of China(Grant No.51876220)the Fundamental Research Funds for the Central Universities(Grant No.ZX20190184).
文摘The interactions between the bubbles and the particles near structures are important issues for the applications of the cavitation in the fluid machinery.To study the hidden microscopic mechanisms,a numerical method for simulating the laser-generated bubble between the solid wall and a particle is developed in this paper with considerations of the viscosities and the compressibility of the gas and the liquid phases,as well as the surface tension between them.The gas-liquid interface is tracked by the coupling level set and the volume of fluid(CLSVOF)method.The numerical results clearly reveal that the particle can influence the cavitation bubble behaviors.The potential damage of the nearby structures is numerically quantified in terms of the wall pressure,which helps better understand the synergetic effects of the particle on the cavitation.The effects of three dimensionless parameters on the wall pressure are also investigated,especially,on the peak pressure,namely,γ1(defined as L_(1)/R_(max),where L_(1)is the distance from the center of the initial bubble to the solid wall and R_(max)is the maximum bubble radius),γ_(2)(defined as L_(2)/R_(max),where L_(2)is the distance from the lower surface of the spherical particle to the initial bubble center)andθ(defined as Rp/R_(max),where Rp is the spherical particle radius).Further numerical results show that these parameters play a dominant role in determining the peak pressure.When y_(1)<1.00,the peak pressure on the solid wall during the bubble collapse is mainly resulted from the liquid jet.Whenγ1>1.00,the peak pressure is caused by the shock wave.With the increase ofθor decrease ofγ_(2),the peak pressure increases.Whenγ_(2)>2.00,the effect of the particle on the bubble behavior can be neglected.
基金Project supported by the National Natural Science Foundation of China (Grant No.51109119)the State key Laboratory of Hydro-science and Engineering,Tsinghua University (Grant No.2011-KY-1)
文摘The Large Eddy Simulation （LES） of the wave breaking over a muddy seabed is carried out with a Coupled Level Set and Volume Of Fluid （CLSVOF） method to capture the interfaces.The effects of the mud on the wave breaking are studied.The existence of a mud layer beneath an otherwise rigid bottom is found to have a similar effect as an increase of the water depth.As compared with the case of a simple rigid bottom,the inception of the wave breaking is evidently delayed and the breaking intensity is much reduced.The dissipation of the wave energy is shown to have very different rates before,during and after the breaking.Before and after the breaking,the mud plays an important role.During the breaking,however,the turbulence as well as the entrainment of the air also dissipate a large amount of energy.
