A numerical model of powder snow avalanches is developed based the tllermal model in the field of fluid mechanics. The model consists of theconservative equation of fluid phase, the conservative equation of the solid phase, the momentum equation and the equation of the kinetic energy of turbulence. Some constitution relationships, i. e. the entrainment coefficients of ambient fluid, the entrainment coefficient of snow particles on the bed and the shape facotors are expressed by the functions of the slope angle. This model is examined by the experimental data of inclined thermals using the mixture of water and solid particles in the laboratory. The numerical calculations are carried out to simulate the powder snow avalanche occurring at the Yokokura, Katsuyama city in Fukui Prefecture. The reasonable numerical results are obtained. It can explain the longitudinal variations of the height, the speed, the concentration of snow particles, the kinetic energy of turbulence and the distructive power of the avalanche.
This paper expounds some important functional multiphase fluids which are related to biological and medical systems. Artificial blood or blood substitute, gel-dispersed fluid, micro capsule dispersed fluid for the intelligent drug delivery system, micelle of liquid crystal, liquid crystal dispersed fluid and thixotropic fluid are explained and their characteristics and applications are discussed.
Gas was injected into a bath through a nozzle attached to an immersed top lance. The injection angle was changed from zero (upward injection) to π/2 (horizontal injection) to investigate the effect of injection angle on the frequency of bubble formation. In the case of upward injection, the direction of the inertia force of injected gas and that of the buoyancy force acting on the injected gas is the same, while in the case of horizontal injection, the two directions are perpendicular to each other. The frequency of bubble formationfB was significantly influenced by the injection angle. It increased monotonically as the injection angle increased from 0 to π/2. An empirical equation was derived for correlating measuredfB data. In addition, the effect of turbulence transition in nozzle flow on the frequency of bubble formation was discussed.
The aim of this papar is to show the mechanism of instability of the Finite Difference Equation (FDE) for a linearized system of Two Fluid Model (TFM) equations by means of the eigenvalues of the coefficient matrix in the modified equation. First, the modified equations of FDE are introduced from the FDE which was obtained by discretizing the linearized system using the two step Lax-Wendroff scheme. Then, we make sure from the modified equations that the instability of the FDE is caused by ill-posedness of original TFM equation system. Furthermore, von Neumann's stability discriminant equation is concretely and analytically expressed by the sum of damping term and growing term, which consist of numerical diffusion from its lowest even order derivative term of the modified equation, and complex eigenvalue due to ill-posedness of the system, respectively. Finally, the influence of these two terms on the stability is directly shown for the various spatial grid sizes.
This papar is concerned with numerical simulation of a bubbly flow which is generated by continuous release of bubbles with various arrangements from the bottom of a vessel in gravitational field. The flow was analyzed as a continuum in which density and viscosity changed owing to existence of the bubbles. The availability of the exact solution of B. B. O.'s equation with constant acceleration during small time interval made it easy to analyze the motion of the bubbles in the flow. The velocity and pressure fields based on one fluid model were calculated using the SIMPLE method. For initially asymmetric arrangement of bubbles or asymmetric release position, the flow tends to be unstable, even if asymmetry is slight. For initially symmetric arrangement, small bubbles, released from symmetric bottom position of a vessel, are caught in vortices generated by rising bubbles and the flow. tends also to be unstable because of the slight difference of number density of the bubbles in the vortices. This tendency becomes to be weak when large bubbles are mixed with the small bubbles.
Two water purification techniques in wide-closed water area polluted by waste water were developed using two types of aeraters which could generate a large quantity of micro-bubbles, which diameters are less than 100 micron, and form large-scale circulating secondary flows in the whole water area. The efficiency of the techniques was experimentally proved for two kinds of waste water quality in fields.The results indicate that the both aeration systems play a great important role of waste water purification and the growth of animals and plants.