论文标题
在湍流热对流中稀释微粒的运输和沉积
Transport and deposition of dilute microparticles in turbulent thermal convection
论文作者
论文摘要
我们分析了湍流雷利 - 贝纳德对流中稀微粒的转运和沉积行为。对$ 10^{8} $的瑞利号（$ ra $）进行二维直接数值模拟，而prandtl编号（$ pr $）为0.71（对应于空气的工作流体）。拉格朗日点粒子模型用于描述湍流中微粒的运动。我们的结果表明，悬浮的颗粒在湍流中均匀分布，小于$ 10^{ - 3} $，它们倾向于以$ 10^{ - 3} \ Lessim st \ Lessim st \ Lessim ST \ Lesssim 10^{ - 2} $聚类为频段。在更大的$ st $时，微粒将在对流中迅速沉积。我们还计算了粒子轨迹的均方位移（MSD）。在短时间间隔，MSD表现出弹道性，并且在垂直和侧向的各向同性方向上是各向同性的。在更长的时间间隔内，MSD反映了颗粒的限制运动，并且在不同方向上是各向异性的。我们进一步获得了壁上粒子沉积位置的相图，并根据粒子的密度和直径确定了三个沉积状态。一个有趣的发现是，分散的颗粒更喜欢沉积在出现热羽的垂直壁上，这可以通过倾斜细胞和改变大规模循环的旋转方向来验证。
We analyze the transport and deposition behavior of dilute microparticles in turbulent Rayleigh-Bénard convection. Two-dimensional direct numerical simulations were carried out for the Rayleigh number ($Ra$) of $10^{8}$ and the Prandtl number ($Pr$) of 0.71 (corresponding to the working fluids of air). The Lagrangian point particle model was used to describe the motion of microparticles in the turbulence. Our results show that the suspended particles are homogeneously distributed in the turbulence for the Stokes number ($St$) less than $10^{-3}$, and they tend to cluster into bands for $10^{-3} \lesssim St \lesssim 10^{-2}$. At even larger $St$, the microparticles will quickly sediment in the convection. We also calculate the mean-square displacement (MSD) of the particle's trajectories. At short time intervals, the MSD exhibits a ballistic regime, and it is isotropic in vertical and lateral directions; at longer time intervals, the MSD reflects a confined motion for the particles, and it is anisotropic in different directions. We further obtained a phase diagram of the particle deposition positions on the wall, and we identified three deposition states depending on the particle's density and diameter. An interesting finding is that the dispersed particles preferred to deposit on the vertical wall where the hot plumes arise, which is verified by tilting the cell and altering the rotation direction of the large-scale circulation.
