Abstract:

The particle vibration in a gas-solid fluidized bed has a significant effect on transfer process. Lattice Boltzmann method coupled with an improved immersed moving boundary method is used to simulate the single particle vibration with different amplitude A/D and frequency k = f_e/f₀, and the effect of two-particle vibration with different arrangement and spacing on the drag coefficient, lift coefficient and vortex shedding frequency. The results show that when one single particle oscillating transversely at Re = 100, with increasing A/D, particle locking range becomes larger and the drag coefficient inside the locking interval is larger than that outside, which is beneficial to transfer process. When one single particle oscillating stream wisely at A/D = 1.50, the fluid flow mode changes from 2S→2P→2P+2S→chaos with increasing k. At the same A/D when k < 1.25, the drag coefficient of the transversely oscillating particles is larger than that of the stream wisely oscillating particles, but when k > 1.25, it is opposite. Therefore, the particle transversely oscillating is more favorable for transport at k < 1.25, and the particle stream wisely oscillating is more favorable for transport at k > 1.25. The formation of mutual inhibition vortices of the series double particles reduces the drag coefficient, which is not conductive to the transfer, on the contrary, the parallel double particles promote the transfer, and the effect is the best when H = 3D. The above numerical results provide an idea for strengthening transfer process.

Key words: lattice Boltzmann method, immersed moving boundary, particle vibration, drag coefficients, vortex shedding, lock-in

摘要：

流化床内部颗粒振动对传递过程有着重要影响。格子Boltzmann方法耦合改进的浸入运动边界法模拟了不同振幅比A/D和频率比k = f_e/f₀下的单颗粒振动情况，并研究了不同排布和间距的双颗粒振动对传递过程中升阻力系数以及涡脱落频率的影响。结果表明，颗粒Reynolds数Re = 100，单颗粒横向振动时，振幅增大导致锁定区间变大，颗粒锁定区间内的曳力系数大于锁定区间外，有利于传递。单颗粒流向振动，A/D = 1.50时，随振动频率增大，流体流动模式为：2S模式 → 2P模式 → 2P+2S模式 → 混沌。相同振幅下k < 1.25时，颗粒横向振动的曳力系数大于流向振动的曳力系数；k > 1.25时则与之相反。因此，当k < 1.25时，横向振动更有利于传递；k > 1.25时，流向振动更有利于传递。串联双颗粒相互抑制涡的形成使曳力系数减小，不利于传递；相反，并联双颗粒促进传递作用，且在间距H = 3D时效果最佳。以上数值结果为强化传递过程提供了一种思路。

关键词: 格子Boltzmann方法, 浸入运动边界法, 颗粒振动, 曳力系数, 泻涡模式, 锁定现象