The characteristics of dynamic pressure in an impinging jet were experimentally studied. The instantaneous signals of dynamic pressure resulted from the turbulence in the jetting fluid were measured through a piezoele...The characteristics of dynamic pressure in an impinging jet were experimentally studied. The instantaneous signals of dynamic pressure resulted from the turbulence in the jetting fluid were measured through a piezoelectric sensor and recorded by a computer. The pressure signals at central axial position of the jetting fluid were sampled at different fluid pressure. The measured signals obviously possessed periodical characteristics. After analyzing the signals with FFT method, it was found that there was an inherent frequency in the dynamic pressure signals. The inherent frequency increases with the average velocity of the jetting fluid at the nozzle outlet, which is consistent with the theoretical analysis. It was supposed that the dynamic pressure signals are transformed from the fluctuating fluid velocities resulted from the turbulence in the jetting fluid. The inherent frequency corresponds to the minimum eddy scale in the turbulent jet. The smaller the eddy scale is, the higher the inherent frequency is. Higher velocity of the fluid at the outlet leads to a stronger turbulent strength. The fluctuation velocities with high inherent frequency resulted in a strong shear force field, which enables the fluid to be micro-mixed fleetly and the agglomerate of solid particles to be dispersed effectively.展开更多
Large-scale molecular dynamics simulations are used to study the dynamic processes of a nano-droplet impacting on hydrophobic surfaces at a microscopic level. Both the impact phenomena and the velocity distributions a...Large-scale molecular dynamics simulations are used to study the dynamic processes of a nano-droplet impacting on hydrophobic surfaces at a microscopic level. Both the impact phenomena and the velocity distributions are recorded and analyzed. According to the simulation results, similar phenomena are obtained to those in macro-experiments. Impact velocity affects the spread process to a greater degree than at a level of contact angle when the velocity is relatively high.The velocity distribution along the X axis during spread is wave-like, either W- or M-shaped, and the velocity at each point is oscillatory; while the edges have the highest spread velocity and there are crests in the distribution curve which shift toward the edges over time. The distribution along the Y axis is <- or >-shaped, and the segments above the middle have the lowest decrease rate in the spreading process and the highest increase rate in the retraction process.展开更多
A Lattice Boltzmann Method (LBM) with two-distribution functions is employed for simulating the two-phase flow induced by a liquid droplet impinging onto the film of the same liquid on solid surface.The model is suita...A Lattice Boltzmann Method (LBM) with two-distribution functions is employed for simulating the two-phase flow induced by a liquid droplet impinging onto the film of the same liquid on solid surface.The model is suitable for solution of twophase flow problem at high density and viscosity ratios of liquid to vapor and phase transition between liquid and its vapor.The roles of the vapor flow,the density ratio of liquid to vapor and the surface tension of the droplet in the splashing formation are discussed.It is concluded that the vapour flow induced by the droplet fall and splash in the whole impinging process may affect remarkably the splash behaviour.For the case of large density ratio of liquid to vapor a crown may engender after the droplet collides with the film.However,for the case of small density ratio of liquid to vapor a "bell" like splash may be observed.展开更多
Y984028 is a new lherzolitic shergottite,consisting of poikilitic and non-poikilitic lithologies.The mafic silicates are FeO-poor,and the chromite is TiO 2-poor in the poikilitic lithology compared to the grains in th...Y984028 is a new lherzolitic shergottite,consisting of poikilitic and non-poikilitic lithologies.The mafic silicates are FeO-poor,and the chromite is TiO 2-poor in the poikilitic lithology compared to the grains in the non-poikilitic lithology.This meteorite shares similarmineral petrography andmineral chemistry with GRV 99027,but is not paired with the latter because of their different shock-induced features.Y984028 was severely shocked and experienced no significant thermal metamorphism after the main impact event.Hence,Y984028 serves as a probe for the study of meteorite impact processes on terrestrial surfaces.The melt veins in Y984028 are characterized by the absence of any high-pressure polymorphs,the presence of abundant smallmineral fragments,and the prevailing granulation textures of olivine and chromite.These features are consistent with adiabatic melting during the release of shock-induced high-pressure and quenching at ambient pressure.展开更多
文摘The characteristics of dynamic pressure in an impinging jet were experimentally studied. The instantaneous signals of dynamic pressure resulted from the turbulence in the jetting fluid were measured through a piezoelectric sensor and recorded by a computer. The pressure signals at central axial position of the jetting fluid were sampled at different fluid pressure. The measured signals obviously possessed periodical characteristics. After analyzing the signals with FFT method, it was found that there was an inherent frequency in the dynamic pressure signals. The inherent frequency increases with the average velocity of the jetting fluid at the nozzle outlet, which is consistent with the theoretical analysis. It was supposed that the dynamic pressure signals are transformed from the fluctuating fluid velocities resulted from the turbulence in the jetting fluid. The inherent frequency corresponds to the minimum eddy scale in the turbulent jet. The smaller the eddy scale is, the higher the inherent frequency is. Higher velocity of the fluid at the outlet leads to a stronger turbulent strength. The fluctuation velocities with high inherent frequency resulted in a strong shear force field, which enables the fluid to be micro-mixed fleetly and the agglomerate of solid particles to be dispersed effectively.
基金supported by the National Natural Science Foundation of China(Grant No.51109178)the Science and Technology Innovation Foundation ofNorthwestern Polytechnical University,China(Grant No.JC20120218)
文摘Large-scale molecular dynamics simulations are used to study the dynamic processes of a nano-droplet impacting on hydrophobic surfaces at a microscopic level. Both the impact phenomena and the velocity distributions are recorded and analyzed. According to the simulation results, similar phenomena are obtained to those in macro-experiments. Impact velocity affects the spread process to a greater degree than at a level of contact angle when the velocity is relatively high.The velocity distribution along the X axis during spread is wave-like, either W- or M-shaped, and the velocity at each point is oscillatory; while the edges have the highest spread velocity and there are crests in the distribution curve which shift toward the edges over time. The distribution along the Y axis is <- or >-shaped, and the segments above the middle have the lowest decrease rate in the spreading process and the highest increase rate in the retraction process.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.10872123,11032007)the Ministry of Education in China (Grant No.IRT0844)+1 种基金the Opening Fund of State Key Laboratory of Nonlinear MechanicsShanghai Program for Innovative Research Team in Universities
文摘A Lattice Boltzmann Method (LBM) with two-distribution functions is employed for simulating the two-phase flow induced by a liquid droplet impinging onto the film of the same liquid on solid surface.The model is suitable for solution of twophase flow problem at high density and viscosity ratios of liquid to vapor and phase transition between liquid and its vapor.The roles of the vapor flow,the density ratio of liquid to vapor and the surface tension of the droplet in the splashing formation are discussed.It is concluded that the vapour flow induced by the droplet fall and splash in the whole impinging process may affect remarkably the splash behaviour.For the case of large density ratio of liquid to vapor a crown may engender after the droplet collides with the film.However,for the case of small density ratio of liquid to vapor a "bell" like splash may be observed.
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-110 and KZCX2-YW-Q08)
文摘Y984028 is a new lherzolitic shergottite,consisting of poikilitic and non-poikilitic lithologies.The mafic silicates are FeO-poor,and the chromite is TiO 2-poor in the poikilitic lithology compared to the grains in the non-poikilitic lithology.This meteorite shares similarmineral petrography andmineral chemistry with GRV 99027,but is not paired with the latter because of their different shock-induced features.Y984028 was severely shocked and experienced no significant thermal metamorphism after the main impact event.Hence,Y984028 serves as a probe for the study of meteorite impact processes on terrestrial surfaces.The melt veins in Y984028 are characterized by the absence of any high-pressure polymorphs,the presence of abundant smallmineral fragments,and the prevailing granulation textures of olivine and chromite.These features are consistent with adiabatic melting during the release of shock-induced high-pressure and quenching at ambient pressure.
