Numerical Simulation Of Flow Stability Of Buoyant-thermocapillary Convective Flow Under Shear Flow

The floating zone method is one of the technologies for the preparation of high quality crystals in industry.The oscillating flow of the melt in the floating zone produces stripes on the surface of the crystal,which seriously affects the quality of the crystal.As a scientific model of the crystal growth technology of the floating zone method,the study of the flow of liquid bridge fluid can further clarify the mechanism of the melt oscillating flow in the floating zone.At present,the method of restraining the flow of fluid inside the liquid bridge has external magnetic field,liquid sealed bridge,and external shear flow.The shear flow is a new way to interfere with the flow field in the liquid bridge,and the foreign and domestic scholars have relatively few studies on it.In this paper,the study is to interfere with the flow field in a liquid bridge by using the shear flow to reaearch the stability of buoyancy and thermal capillary convective.The research method of this paper is to write the corresponding program through the UDF of FLUENT to make the gas-liquid interface of the liquid bridge coupled together to enable the transfer of energy and momentum;By changing the temperature of the upper and lower rods of the liquid bridge,the flow velocity and direction of the shear airflow,the volume ratio of liquid to bridge fluid,the temperature of the shear airflow,we explore the flow stability of the liquid bridge's internal flow field.The research of this paper is divided into two parts:steady flow and oscillating flow.The results of this study are as follows:The study of steady flow:(1)The flow structure inside a liquid bridge under the action of shear flow:Initial state of single vortex core is formed by shear force in a liquid bridge.With the development of the flow,the flow field in the liquid bridge develops into three vortices with thermal capillary convection vortex center,shear flow force vortex center and flow vortex center.Then thermal capillary convective vortices compresses the vortex center of the shear gas until the center of the vortex disappears and presents the state of a single vortex.Then,the double vorticity state is formed by the thermal capillary convection near near the free surface.Finally,the buoyancy convective vortex center is formed by the buoyancy convection in the middle axis,and the whole liquid bridge presents a state of three vortices;(2)For the upper ventilation situation:the increase of the velocity of the shear flow and the increase of the volume ratio can cause the debilitating of the buoyancy convection vortex center and the the upper vortex center of thermal convection,and the growth of lower side of the vortex center of thermal convection;For the lower ventilation situation:the increase of the velocity of shear flow can make the buoyancy convective vortex center and the lower side vortex center of thermal capillary convection grow;The increase of the volume ratio causes the lower vortex center to gradually squeeze the vortex center on the upper side;(3)For the lower ventilation situation:the increase of the temperature difference between the upper and lower rad can increase the lower vorticity of the thermal capillary convection.The increase in the temperature of the shear flow can cause the decay of the lower side vortex center of thermal capillary convection and the expansion of the convective vortex center of the buoyancy.The study of oscillation flow:(1)The oscillation of the flow field in the liquid bridge is the result of the competition between the buoyancy convection and the thermal capillary convection.The oscillations of temperature and velocity on the free surface originate from the hot end,but at the half height of the liquid bridge,the velocity and temperature oscillate in the opposite direction,and the velocity oscillation is transmitted from the axis of liquid bridge to the free surface;(2)The critical starting time of the flow field transition can be delayed by increasing the velocity of shear flow,increasing the temperature of the shear flow and increasing the volume ratio.