基于LBM-DEM耦合模型的多孔射流喷动床内流动特性

Flow characteristics in porous jet spouted bed with LBM-DEM coupled model

研究喷动床内颗粒的流动特性对于喷动床的设计和优化具有重要意义。基于格子Boltzmann方法(LBM)-离散单元法(DEM)的数学模型,综合考虑固体运动对流场的影响,气相采用修正后的格子Boltzmann方程计算,颗粒-颗粒以及颗粒-壁面之间的碰撞采用离散单元法软球模型,颗粒所受气体曳力采用Gidaspow曳力模型,流固耦合基于牛顿第三定律,从介观角度深入剖析了多孔射流稠密气固流化床内流动机理。采用Fortran语言编程对上述模型进行求解,通过复现气泡在鼓泡床中的演化过程,有效验证了LBM-DEM耦合模型的准确性。研究了单喷口系统与多喷口系统在不同射流速度下的空隙率、颗粒拟温度、床层膨胀高度以及颗粒动能与势能等典型参数变化。结果表明:单喷口射流气速增加时,气体对颗粒的携带能力增强,喷泉区扩大,床内空隙率分布增大,速度脉动变大,颗粒拟温度升高,床层膨胀高度提高;而在多喷口系统中,相邻喷口间存在较强的横向扰动,在床层底部喷泉区出现明显射流合并,位于中心射流区域的颗粒获得较高动量,喷口数的增加使得床层膨胀高度提高27.50%,时均空隙率范围扩大,颗粒拟温度升高,且射流合并高度随喷口数量的增加而降低28.57%,颗粒势能增加66.07%,动能减少48.48%。以上分析结果表明基于修正格子Boltzmann方法与离散单元法相结合的耦合模型可以作为分析稠密气固两相流内在机理的有效工具。

It is important to study the flow characteristics of particles in spouted bed for the design and optimization.Based on the lattice Boltzmann method (LBM)-discrete element method (DEM),considering the influence of solid motion on the flow field comprehensively,the gas phase is calculated by the modified lattice Boltzmann equation,the collision between particles and particle-wall is calculated by the soft sphere model of discrete element method,the gas drag force of particles is modeled by the Gidaspow drag force model,and the fluid-solid coupling is based on the Newton’s third law.The flow mechanism of porous jet in the dense gas-solid fluidized bed is analyzed from the mesoscopic point of view.The above model is solved by Fortran language programming.The accuracy of LBM-DEM coupling model is validated effectively by reproducing the evolution process of bubbles in bubbling bed.The variation of void fraction,particle pseudo-temperature,bed expansion height,particle kinetic energy and potential energy of single-nozzle system and multi-nozzle system at different jet velocities are studied.The results show that with the increase of gas velocity of single nozzle jet,the carrying capacity of gas to particles increases,the fountain area enlarges,the voidage distribution in the bed increases,the velocity fluctuation increases,the pseudo-temperature of particles increases,and the expansion height of the bed increases.In multi-nozzle system,there is strong lateral disturbance between adjacent nozzles,and obvious jet coalescence occurs in the fountain area at the bottom of the bed,which is located at the center of the jet.With the increase of nozzle number,the bed expansion height increases by 27.50%,the time-averaged voidage range enlarges,the particle pseudo-temperature increases,the jet merging height decreases by 28.57%,the particle potential energy increases by 66.07%,and the kinetic energy decreases by 48.48%.The above analysis results show that the coupled model based on the modified lattice Boltzmann method and discrete element method can be used as an effective tool to analyze the internal mechanism of dense gas-solid two-phase flow.