In this paper,we study the onset and development of three-dimensional convection in a tilted porous layer saturated with a liquid.The layer is subjected to a gravitational field and a strictly vertical temperature gra...In this paper,we study the onset and development of three-dimensional convection in a tilted porous layer saturated with a liquid.The layer is subjected to a gravitational field and a strictly vertical temperature gradient.Typically,problems of thermal convection in tilted porous media saturated with a liquid are studied by assuming constant different temperatures at the boundaries of the layer,which prevent these systems from supporting conductive(non-convective)states.The boundary conditions considered in the present work allow a conductive state and are representative of typical geological applications.In an earlier work,we carried out a linear stability analysis of the conductive state.It was shown that at any layer tilt angles,the most dangerous type of disturbances are longitudinal rolls.Moreover,a non-zero velocity component exists in z-direction.In the present work,threedimensional non-linear convection regimes are studied.The original three-dimensional problem is reduced to two-dimensional one with an analytical expression for the velocity z-component v_(z)=v_(z)(x,y).It is shown that the critical Rayleigh number values obtained through numerical solutions of the obtained 2D problem by a finite difference method for different layer inclination angles,are in a good agreement with those predicted by the linear theory.The number of convective rolls realized in nonlinear calculations also fits the linear theory predictions for a given cavity geometry.Calculations carried out at low supercriticalities show that a direct bifurcation takes place.With increasing supercriticality,no transitions to other convective regimes are detected.The situation studied in this problem can be observed in oil-bearing rock formations under the influence of a geothermal temperature gradient,where the ensuing fluid convection can affect the distribution of oil throughout the layer.展开更多
In the present work, the microstructures of A356 feedstock cast via a pipe consisting of partial inclined and partial vertical sections were investigated. The experimental results indicate that semisolid feedstock wit...In the present work, the microstructures of A356 feedstock cast via a pipe consisting of partial inclined and partial vertical sections were investigated. The experimental results indicate that semisolid feedstock with ideal microstructures can be obtained at higher temperatures 645℃ and above by the proposed process, and the solid shell inside the pipe can be avoided at the optimum pouring temperature. Thus the process is attractive for industrial applications. The slanted angle of inclined section has an influence on the optimum pouring temperature. That is, the bigger the slanted angle, the higher the optimum pouring temperature, but accordingly, the greater the possibility of solid shell occurring inside the pipe. Therefore, small slanted angle should be considered first on the premise of ensuring a certain nucleation. The formation of semisolid feedstock is owed to the coactions of wall nucleation and stirring resulting from fluid flow. The inclined section greatly affects nucleation, and the vertical section has an important effect on both nucleation and generating stirring.展开更多
基金financial support from the Ministry of Science and Higher Education of the Russian Federation(Topic No.121031700169-1).
文摘In this paper,we study the onset and development of three-dimensional convection in a tilted porous layer saturated with a liquid.The layer is subjected to a gravitational field and a strictly vertical temperature gradient.Typically,problems of thermal convection in tilted porous media saturated with a liquid are studied by assuming constant different temperatures at the boundaries of the layer,which prevent these systems from supporting conductive(non-convective)states.The boundary conditions considered in the present work allow a conductive state and are representative of typical geological applications.In an earlier work,we carried out a linear stability analysis of the conductive state.It was shown that at any layer tilt angles,the most dangerous type of disturbances are longitudinal rolls.Moreover,a non-zero velocity component exists in z-direction.In the present work,threedimensional non-linear convection regimes are studied.The original three-dimensional problem is reduced to two-dimensional one with an analytical expression for the velocity z-component v_(z)=v_(z)(x,y).It is shown that the critical Rayleigh number values obtained through numerical solutions of the obtained 2D problem by a finite difference method for different layer inclination angles,are in a good agreement with those predicted by the linear theory.The number of convective rolls realized in nonlinear calculations also fits the linear theory predictions for a given cavity geometry.Calculations carried out at low supercriticalities show that a direct bifurcation takes place.With increasing supercriticality,no transitions to other convective regimes are detected.The situation studied in this problem can be observed in oil-bearing rock formations under the influence of a geothermal temperature gradient,where the ensuing fluid convection can affect the distribution of oil throughout the layer.
基金supported by the National KeyBasic Research Foundation of China under grant No.2006CB605203the National Hi-Tech Research Founda-tion of China under grant No. 2006AA03Z115 the National Natural Science Foundation of China under grantNo.50774007.
文摘In the present work, the microstructures of A356 feedstock cast via a pipe consisting of partial inclined and partial vertical sections were investigated. The experimental results indicate that semisolid feedstock with ideal microstructures can be obtained at higher temperatures 645℃ and above by the proposed process, and the solid shell inside the pipe can be avoided at the optimum pouring temperature. Thus the process is attractive for industrial applications. The slanted angle of inclined section has an influence on the optimum pouring temperature. That is, the bigger the slanted angle, the higher the optimum pouring temperature, but accordingly, the greater the possibility of solid shell occurring inside the pipe. Therefore, small slanted angle should be considered first on the premise of ensuring a certain nucleation. The formation of semisolid feedstock is owed to the coactions of wall nucleation and stirring resulting from fluid flow. The inclined section greatly affects nucleation, and the vertical section has an important effect on both nucleation and generating stirring.
