Research on Deposition and Orientation Characteristics of Cylindrical Particles in Gas-Solid 2-Phase Turbulent Flow in Curved Tubes
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摘要:
针对在Reynolds数Re=3000 ~ 50000、Stokes数Stk=0.1 ~ 10、Dean数De=1400 ~ 2800的情况下，长径比β=2 ~ 12的圆柱状颗粒流经弯管湍流场时的取向与沉积特性进行了研究。圆柱状颗粒的运动采用细长体理论结合Newton第二定律进行描述，取向分布函数由Fokker-Planck方程给出，平均湍流场通过求解Reynolds平均运动方程结合Reynolds应力方程得到，作用在颗粒上的湍流脉动速度由动力学模拟扫掠模型描述。通过求解湍流场以及颗粒的运动方程和取向分布函数方程，得到并分析了沿流向不同截面和出口处颗粒的取向分布，讨论了各因素对颗粒沉积特性的影响。研究结果表明，随着Stk和颗粒长径比β的增加、De和Re的减少，颗粒的主轴更趋向于流动方向。颗粒的沉积率随着De，Re，Stk和颗粒长径比的增大而增加，所得结论对于工程实际应用具有参考价值。
Abstract:In the cases of Reynolds number Re=3 000~50 000, Stokes number Stk=0.1~10, Dean number De=1 400~2 800, the orientation and deposition characteristics of cylindrical particles with aspect ratio β=2~12 in turbulent flow in curved tubes were studied. The motion of cylindrical particles was described under the slender body theory combined with Newton’s 2nd law. The orientation distribution function of cylindrical particles was given by the Fokker Planck equation. The mean velocity of the flow was obtained by solving the Reynolds-averaged Navier-Stokes equation and the Reynolds stress equation. The turbulent fluctuating velocity acting on particles was described with the kinetic simulation sweeping model. By solving the equations of the turbulent flow, the particle motion and the orientation distribution function, the orientation distributions of particles on the cross sections in different axial positions and the outlet were obtained and analyzed. The effects of various parameters on the deposition rate of particles were discussed. The results showed that, the main axis of particles turns toward the flow direction with the increase of Stk and β, and the decrease of De and Re. The deposition rate of particles increases with De, Re and β. However, it shows a non-monotonic trend with the change of Stk
. The work has reference values for practical engineering application.
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图 4 平均轴向速度和轴向脉动速度均方根的分布(Re=10500, De=2460)：（a） 平均轴向速度；（b） 轴向脉动速度均方根
Figure 4. Distributions of the mean axial velocity and the RMS value of the fluctuating axial velocity (Re=10500, De=2460): (a) the mean axial velocity; (b) the RMS value of the fluctuating axial velocity
图 5 横截面上颗粒平均取向分布(Re=30000, Stk = 1, De=2200，β=8)
Figure 5. Distributions of mean orientations of particles on the cross section (Re =30000, Stk =1, De=2200，β=8)
图 6 不同Stk时，颗粒平均取向分布(Re=30000, De=2200, β=8)
Figure 6. Distributions of particle orientations for different Stk values (Re =30000, De =2200, β=8)
图 7 不同De时，颗粒平均取向分布(Re =30000, Stk=1, β=8)
Figure 7. Distributions of particle orientations for different De values (Re=30000, Stk=1, β=8)
图 8 不同Re时，颗粒取向分布(De=2200, Stk=1, β=8)
Figure 8. Distributions of particle orientations for different Re values (De=2200, Stk=1, β=8)
图 9 不同β时，颗粒取向分布(Re=30000, De =2200, Stk=1)
Figure 9. Distributions of particle orientations for different β values (Re=30000, De =2200, Stk=1)
图 10 不同Stk下的颗粒通过率(De=1862, Re=10500, β=1)
Figure 10. The pass ratio of particles at different Stk values (De=1862, Re=10500, β=1)
图 11 不同颗粒长径比时沉积率与Stk的关系(Re=30000, De=2200)
Figure 11. The relationship between the deposition rate and Stk at different particle aspect ratios (Re=30000, De=2200)
图 12 不同Re下沉积率与Stk的关系(De=2200, β=8)
Figure 12. The relationship between the deposition rate and Stk at different Re values (De =2200, β=8)
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