Numerical simulation based on phase field method is performed to describe solidification process of pure material in a free or forced flow. The evolution of the interface is showed, and the effects of mesh grid and fl...Numerical simulation based on phase field method is performed to describe solidification process of pure material in a free or forced flow. The evolution of the interface is showed, and the effects of mesh grid and flow velocity on succinonitrite shape are studied. These results indicate that crystal grows into an equiaxial dendrite in a free flow and into an asymmetrical dendritic in a forced flow. With increasing flow velocity, the upstream dendritic arm tip grows faster and the downstream arm grows slower. However, the evolution of the perpendicular tip has no significant change. In addition, mesh grid has no influence on dendritic growth shape when mesh grid is above 300×300.展开更多
Numerical simulation based on phase field method was performed to describe the solidification of silicon. The effect of anisotropy, undercooling and coupling parameter on dendrite growth shape was investigated. It is ...Numerical simulation based on phase field method was performed to describe the solidification of silicon. The effect of anisotropy, undercooling and coupling parameter on dendrite growth shape was investigated. It is indicated that the entire facet dendrite shapes are obtained by using regularized phase field model. Steady state tip velocity of dendrite drives to a fixed value when γ≤0.13. With further increasing the anisotropy value, steady state tip velocity decreases and the size is smaller. With the increase in the undercooling and coupling parameter, crystal grows from facet to facet dendrite. In addition, with increasing coupling parameter, the facet part of facet dendrite decreases gradually, which is in good agreement with Wulff theory.展开更多
Numerical simulation based on phase field method was developed to describe the solidification of two-dimensional isothermal binary alloys. The evolution of the interface morphology was shown and the effects of phase f...Numerical simulation based on phase field method was developed to describe the solidification of two-dimensional isothermal binary alloys. The evolution of the interface morphology was shown and the effects of phase field parameters were formulated for succinonitrile-acetone alloy. The results indicate that an anti-trapping current(ATC) can suppress many trapped molten packets, which is caused by the thickened interface. With increasing the anisotropy value from 0 to 0.05, a small circular seed grows to develope secondary dendritic, dendritic tip velocity increases monotonically, and the solute accumulation of solid/liquid interface is diminished distinctly. Furthermore, with the increase of the coupling parameter value, the interface becomes unstable and the side branches of crystals appear and grow gradually.展开更多
Based on schlieren imaging method the shock wave generated by diesel injector has been investigated,and the influences of ambient gas property, the progress of the spray, ambient gas density and ambient gas temperatur...Based on schlieren imaging method the shock wave generated by diesel injector has been investigated,and the influences of ambient gas property, the progress of the spray, ambient gas density and ambient gas temperature on shock wave have been analyzed. The results show that:the images of spray shock wave are cleaner using sulfur hexafluoride(SF6) as ambient gas than using the nitrogen(N2); at the beginning of injection, shock wave phenomenon does not generate immediately as the fuel leave the nozzle because of the needle movement, and the hesitation is decided by the injection condition and characteristics of injector. The generation of shock wave in the spray tip and the detachment of shock wave from the spray tip show little effect on the spray macroscopic characteristics. The ambient gas density and temperature have a significant effect on the maximum of spray tip velocity, types of shock wave and the detachment timing of shock wave from the spray tip.展开更多
The formula for the analytical calculations of the shaped charge jetting parameters exhibit an explicit dependence upon the Gurney velocity of an explosive material.Many attempts have been done to approximate the char...The formula for the analytical calculations of the shaped charge jetting parameters exhibit an explicit dependence upon the Gurney velocity of an explosive material.Many attempts have been done to approximate the characteristic constant 2E^(1/2) and to make its use more efficient.It is shown herein that the characteristic Gurney velocity parameter depends on the ratio of the Chapman Jouguet-pressure to explosive impulse ratio by the formula:2E^(1/2)=0.2415(P_(CJ)/I_(SP)ρ_0)-970.76,where PCJis the Chapman Jouguet pressure(Pa),ISPis the specific impulse of the explosive used as a monopropellant(N·s/kg)andρois the explosive density(kg/m^3).The proposed empirical formula was found to be reasonable and quite accurate approximation that can be implemented over a wide range of explosives,where the maximum deviation between the measured and the calculated Gurney velocities was nearly 6%.Besides,the proposed approach has been used analytically to calculate the jet tip velocity of a small caliber shaped charge,which is measured experimentally.The difference between the measured and the calculated jet tip velocity was only 1.6%.展开更多
基金supported by the Major Program of the National Natural Science Foundation of China (Nos.50331040 and 60171034).
文摘Numerical simulation based on phase field method is performed to describe solidification process of pure material in a free or forced flow. The evolution of the interface is showed, and the effects of mesh grid and flow velocity on succinonitrite shape are studied. These results indicate that crystal grows into an equiaxial dendrite in a free flow and into an asymmetrical dendritic in a forced flow. With increasing flow velocity, the upstream dendritic arm tip grows faster and the downstream arm grows slower. However, the evolution of the perpendicular tip has no significant change. In addition, mesh grid has no influence on dendritic growth shape when mesh grid is above 300×300.
基金Projects(50331040 60171034) supported by the National Natural Science Foundation of China
文摘Numerical simulation based on phase field method was performed to describe the solidification of silicon. The effect of anisotropy, undercooling and coupling parameter on dendrite growth shape was investigated. It is indicated that the entire facet dendrite shapes are obtained by using regularized phase field model. Steady state tip velocity of dendrite drives to a fixed value when γ≤0.13. With further increasing the anisotropy value, steady state tip velocity decreases and the size is smaller. With the increase in the undercooling and coupling parameter, crystal grows from facet to facet dendrite. In addition, with increasing coupling parameter, the facet part of facet dendrite decreases gradually, which is in good agreement with Wulff theory.
基金Projects(50331040 60171034) supported by the National Natural Science Foundation of China
文摘Numerical simulation based on phase field method was developed to describe the solidification of two-dimensional isothermal binary alloys. The evolution of the interface morphology was shown and the effects of phase field parameters were formulated for succinonitrile-acetone alloy. The results indicate that an anti-trapping current(ATC) can suppress many trapped molten packets, which is caused by the thickened interface. With increasing the anisotropy value from 0 to 0.05, a small circular seed grows to develope secondary dendritic, dendritic tip velocity increases monotonically, and the solute accumulation of solid/liquid interface is diminished distinctly. Furthermore, with the increase of the coupling parameter value, the interface becomes unstable and the side branches of crystals appear and grow gradually.
基金supported by the National Natural Science Foundation of China (51076118, 51006075)the Fundamental Research Funds for the Central Universities (1700219089)+1 种基金China Postdoctoral Science Foundation (2013M531209)Shanghai Rising-Star Program (11QH1402500)
文摘Based on schlieren imaging method the shock wave generated by diesel injector has been investigated,and the influences of ambient gas property, the progress of the spray, ambient gas density and ambient gas temperature on shock wave have been analyzed. The results show that:the images of spray shock wave are cleaner using sulfur hexafluoride(SF6) as ambient gas than using the nitrogen(N2); at the beginning of injection, shock wave phenomenon does not generate immediately as the fuel leave the nozzle because of the needle movement, and the hesitation is decided by the injection condition and characteristics of injector. The generation of shock wave in the spray tip and the detachment of shock wave from the spray tip show little effect on the spray macroscopic characteristics. The ambient gas density and temperature have a significant effect on the maximum of spray tip velocity, types of shock wave and the detachment timing of shock wave from the spray tip.
文摘The formula for the analytical calculations of the shaped charge jetting parameters exhibit an explicit dependence upon the Gurney velocity of an explosive material.Many attempts have been done to approximate the characteristic constant 2E^(1/2) and to make its use more efficient.It is shown herein that the characteristic Gurney velocity parameter depends on the ratio of the Chapman Jouguet-pressure to explosive impulse ratio by the formula:2E^(1/2)=0.2415(P_(CJ)/I_(SP)ρ_0)-970.76,where PCJis the Chapman Jouguet pressure(Pa),ISPis the specific impulse of the explosive used as a monopropellant(N·s/kg)andρois the explosive density(kg/m^3).The proposed empirical formula was found to be reasonable and quite accurate approximation that can be implemented over a wide range of explosives,where the maximum deviation between the measured and the calculated Gurney velocities was nearly 6%.Besides,the proposed approach has been used analytically to calculate the jet tip velocity of a small caliber shaped charge,which is measured experimentally.The difference between the measured and the calculated jet tip velocity was only 1.6%.
