Simulation Of Drag Force For Irregular Particle And Multi-particles Using The Lattice Boltzmann Method

Gas-solid tow-phase flow is very common in various industrial practice. In particular, there exists a lot of complex irregular particles and multi-particles in coal-fired power plant boilers. The properties of irregular particle and multi-particles in impressible viscous flow were investigated in this paper, especially the drag force of particles. To be specific, the following conclusions can be drawn.Starting from the flow past cylinder and sphere, the drag and lift coefficients and strouhal number were calculated among various Reynolds number and shown a great agreement with the others, which ensures the reliability of LBM method.Secondly, the pressure drop in Stokes flow of four non-circular particles, including triangular, quatrefoil, trilobal and rectangular particles, was calculated. The triangular and trilobal particles have the same structure and show that they both have the largest pressure drop when placed 0° degree, and get a smaller pressure drop when orientation angle is larger. The quatrefoil particle is very insensitive to the orientation angle while the rectangular particle is the most sensitive. Comparison of four kinds of particles shows that the rectangular particle with 0° degree has the minimal pressure drop while trilobal particle has the maximum when placed 0° and ?= 2.Thirdly, the flow properties and drag force of simple particle array, eight-particle array and random particles were investigated. The hard sphere Monte Carlo method was used to generate the random particles. The quantitative relationship between drag force of simple particle array and volume fraction was validated. For eight-particle array, the flow velocity of mainstream direction at the central point increases with the increase of Reynolds number, and shows a good agreement with the experimental results. And for random particles, the probability density of velocity at the void space peaks at vz=0 with larger volume fraction, then shows a bimodal distribution when volume fraction decreases to 0.35 and finally shows a unimodal distribution when volume fraction continues to decrease. In addition, the probability density of normalize drag force of random particles satisfies a Gaussian distribution with average value of one and standard deviation of 0.518.Fourthly, the drag force of two-dimensional point-source aggregates and three-dimensional finite size particle aggregates in Stokes flow was investigated. For 2D problems, the isotropy of aggregate is weak for fewer particles, which shows a great difference between various flow directions. Then, we got a fitting formula to calculate the drag force of 2D aggregate with various volume fractions based on the existing formula of cylinders. Besides, the quantitative relations between drag force and particle number and projected area for 3D aggregates were also obtained.Finally, two more special conditions considering slip boundary and particle moving were studied. The flow past cylinder with slip boundary was simulated at various Reynolds number and Knudsen number. Then the sedimentation of single particle in two-dimensional channel was simulation and the terminal sedimentation velocity and drag force of particle were also calculated.