Marangoni-thermocapillary Convection Under Coupling Effect Of Axial Magnetic Field And Pool Rotation In Shallow Annular Pool

There is fluid flow on the free interface submitted to the uneven distribution of surface tension,which is induced by the temperature gradient.The flow is named Marangoni convection or thermocapillary convection: one is Marangoni convection caused by the temperature gradient perpendicular to the free interface,and the other one is thermocapillary convection is caused by temperature gradient parallel to the free interface.There is Marangoni-thermocapillary convection in the process of crystal growth by Czochralski method,which will complicate melt flow and reduce the quality of crystal growth.At present,there have been numbers of research studies on Marangoni-thermocapillary convection under a single external force,but few studies have been done on coupling various external forces.The effect of coupling multiple forces on Marangoni-thermocapillary convection is better than that of single external force.Therefore,the Marangoni-thermocapillary convection in an annular shallow pool is studied by coupling axial magnetic field and pool rotation.The effects of axial magnetic field,pool rotation and their coupling on Marangoni-thermocapillary convection are studied by means of three-dimensional numerical simulation,and the flow mechanism is analyzed.The results are helpful to enrich and develop the dissipative structure theory of complex flow in liquid layer and provide theoretical guidance for the crystal growth.The main works and results are list as follows:Firstly,a series of three-dimensional numerical simulations of Marangonithermocapillary convection are carried out,which is under the interaction of horizontal temperature gradient and heat flux on the bottom in a shallow annular pool.Three different flow states(three-dimensional steady flow,periodic oscillatory flow and aperiodic oscillatory flow)are determined and their characteristics are analyzed.Secondly,the effects of axial magnetic field,pool rotation and their coupling on the steady Marangoni-thermocapillary convection are studied.It is found that they have different restraining effects on temperature fluctuation,radial flow and circumferential flow.In order to suppress the three-dimensional steady flow into axisymmetric steady state,it is needed to apply a higher rotation rate under the smaller magnetic field intensity.Thirdly,the effects of axial magnetic field,pool rotation and their coupling on the periodic oscillatory Marangoni-thermocapillary convection are studied.It is found that they all change the free surface temperature fluctuation structure.The instability of the flow will be enhanced under the slight external force.The mechanism of flow transition is explained by analyzing the process of flow transition under the action of each of them.In order to suppress the three-dimensional steady flow into axisymmetric steady state,it is needed to apply a lower rotation rate under the larger magnetic field intensity.Finally,the effects of axial magnetic field,pool rotation and their coupling on the non-periodic oscillatory Marangoni-thermocapillary convection are studied.It is found that the pool rotation enhances the radial flow and a higher rotation rate will lead to a further enhancement.The temperature fluctuation structure on the free surface will change many times when the magnetic field intensity or the rotation rate increases.In order to suppress the aperiodic oscillatory flow to axisymmetric steady state,it is needed to apply a higher rotation rate under the larger magnetic field intensity.