An Improved Two-phase Lattice Boltzmann Model And Its Applications In Magnetic Fluid Sensor

Magnetic fluid is a new functional material with both fluidity and magnetism,and its application fields are very wide.Magnetic fluid sensor is one of the applications with unique properties of magnetic fluid,and it is also a main direction of the development of new materials used in sensors.At present,magnetic fluid sensors have been widely used in structural health monitoring and detection.Compared with the traditional acceleration sensors,magnetic fluid acceleration sensors have the advantages of high sensitivity,high precision and short response time,etc.However,the existing magnetic fluid acceleration sensors are usually capacitors or inductance,which results in large volume and mass of sensors.With the development of science and technology,sensors are developing towards lost cost,high sensitivity and miniaturization.In this paper,based on lattice Boltzmann method,a two-phase flow model with mass conservation and accurate interface capture is developed,and the dynamic behaviors of the two-phase flow in the magnetic fluid sensors are studied.The present researches can provide theoretical guidance for the design of low-cost,high-sensitivity and miniaturized magnetic fluid sensors.The flow mechanism affects the macro characteristics,which is the key of magnetic fluid control technology.In fact,the motion of bubbles in the magnetofluid is influenced by many factors,and the its motion behavior and mechanism are very complex.Therefore,it is very important to study the influence of magnetic field on bubbles and the flow characteristics of magnetic fluid two-phase flow,and grasp the characteristics of multi-field coupling and interface interference in two-phase flow of magnetic fluid.The present research work is as follows:(1)A lattice Boltzmann model with mass conservation for simulating two-phase flow,which is based on the Z-S-C model proposed by Shao et al,is presented.A mass correction is introduced into the interfacial lattice Boltzmann equation(LBE)to compensate the mass losses or offset the mass increases caused by the numerical and modeling diffusion.Through a series of classical validation examples,it is verified that the present model has a good performance of maintaining mass conservation.(2)An interfacial lattice Boltzmann flux solver(ILBFS),which is based on lattice Boltzmann method(LBM)and traditional methods,is proposed to solve multiphase flow with large density ratio.In the ILBFS,the physical variables at cell centers are given from the solution of macroscopic governing differential equation by the finite volume method.At each cell interface,the inviscid and viscous fluxes in the Cahn-Hilliard equation are evaluated simultaneously by local reconstruction solution of the standard LBE.The reliability and high accuracy of ILBFS capturing the interface of multiphase flow are verified by several benchmark problems.(3)A numerical framework,based on the mass correction model,ILBFS proposed previously and the magnetic self-correcting process,is established,and its reliability and effectiveness are verified by simulating deformation of a ferrofluid droplet under a uniform magnetic field.(4)According to the working principle magnetic fluid two-phase flow sensor,the numerical simulation of magnetic two-phase flow in the sensor was carried out when the sensor was placed horizontally,longitudinally and affected by vibration flow.The effects of magnetic field intensity,magnetic susceptibility,viscous force and surface tension on bubble deformation and motion in magnetic fluid sensor and the influence of dynamic behavior on the change of magnetic flux were explore.In view of the situation of the magnetic fluid two-phase flow sensor placed horizontally and longitudinally,the results show that the shape of the bubble in the magnetic fluid two-phase flow sensor will not cause the change of magnetic flux in the magnetic field region,and thus the induced electromotive force will not be generated,and the volume fraction of the bubble in the magnetic field region will cause the magnetic flux to change,thus the induced electromotive force can be generated.At the same time,the influence of the horizontal sinusoidal vibration flow on the bubble volume and magnetic flux in the magnetic field region is also explored.When the magnetic flux of a single bubble is affected by the sinusoidal magnetic flux,it can be found that the volume and magnetic flux of bubbles in the magnetic field fluctuate sinusoidally,which can produce induced electromotive force.Moreover,when the magnetic field is slightly wider than the initial diameter of the bubble,it is more sensitive to detect the vibration signal source.