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arXiv 1906.01249physics.flu-dyncond-mat.soft
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湍流槽道流中小惯性颗粒的界面解析模拟

Interface-resolved simulations of small inertial particles in turbulent channel flow

Pedro Costa, Luca Brandt, Francesco Picano

AI总结:

本文通过界面解析与单向耦合点粒子DNS的直接对比,研究了湍流槽道流中小惯性颗粒的动力学,发现近壁区因强剪切诱导升力导致两者统计结果存在显著定性差异。

摘要:

我们展示了界面解析与单向耦合点粒子直接数值模拟(DNS)之间的直接比较,研究对象为无重力、且含有小惯性颗粒的湍流槽道流,颗粒-流体密度比高,直径约为 $3$ 个粘性单位。在所考虑的最稀疏流动中,固相体积分数为 $O(10^{-5})$,颗粒对流动的反馈可忽略不计;而在体积分数为 $O(10^{-4})$ 时,发现了与无载荷情况的显著差异,特别是阻力增加了约 $10\%$。这归因于由湍泳效应在壁面引起的致密颗粒层,该层以较大的颗粒-流体表观滑移速度流动。因此,将最稀疏的情况作为基准,以评估一种广泛使用的点粒子模型的有效性,该模型中颗粒动力学仅由惯性力和非线性阻力产生。在槽道主体中,点粒子DNS得到的颗粒速度一阶和二阶矩与界面解析DNS的结果吻合良好。然而,在近壁面区域,大多数统计量显示出重大的定性差异。我们表明,这种差异源于近壁区域作用在颗粒上的强剪切诱导升力。Saffman(J. Fluid Mech., vol. 22 (2), 1965, pp. 385--400)提出的升力模型很好地捕捉了这一机制,而其他旨在更宽颗粒雷诺数范围内扩展升力模型、更为复杂的常用方法,实际上可能会低估本文分析情况下近壁颗粒速度脉动的幅度。

英文摘要:

We present a direct comparison between interface-resolved and one-way-coupled point-particle direct numerical simulations (DNS) of gravity-free turbulent channel flow laden with small inertial particles, with high particle-to-fluid density ratio and diameter of about $3$ viscous units. The most dilute flow considered, solid volume fraction $O(10^{-5})$, shows the particle feedback on the flow to be negligible, whereas differences with respect to the unladen case, noteworthy a drag increase of about $10\%$, are found for a volume fraction $O(10^{-4})$. This is attributed to a dense layer of particles at the wall, caused by turbophoresis, flowing with large particle-to-fluid apparent slip velocity. The most dilute case is therefore taken as the benchmark for assessing the validity of a widely used point-particle model, where the particle dynamics results only from inertial and nonlinear drag forces. In the bulk of the channel, the first- and second-order moments of the particle velocity from the point-particle DNS agree well with those from the interface-resolved DNS. Close to the wall, however, most of the statistics show major qualitative differences. We show that this difference originates from the strong shear-induced lift force acting on the particles in the near-wall region. This mechanism is well captured by the lift force model due to Saffman (J. Fluid Mech., vol. 22 (2), 1965, pp. 385--400), while other widely used, more elaborate, approaches aiming at extending the lift model for a wider range of particle Reynolds numbers can actually underpredict the magnitude of the near-wall particle velocity fluctuations for the cases analysed here.

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