Abstract Laboratory experiments were conducted to study the dynamics of particle clouds released vertically downward into stagnant water. The importance of nozzle diameter, sand particle mass, and particle size were studied in the form of an aspect ratio and Stokes number. The axial and radial profiles of sand concentration and velocity of particle clouds were measured by an accurate and robust optical probe (PV6). Empirical formulations were developed to explain the variations in sand concentration and velocity profiles. It was found that the zone of jet development was smaller in particle clouds than in single-phase water jets and sand jets. Laboratory measurements also indicated that the centerline sand concentration in particle clouds decreased with a slower rate in comparison to single-phase buoyant and sand jets. Important parameters such as mass, momentum fluxes, and drag and entrainment coefficients were calculated inside particle clouds to better understand the evolution of particle clouds in stagnant water. The radial variation of drag coefficient indicated a particle grouping effect in the core region of particle clouds where the drag coefficients decreased from 0.4 to less than 0.1. The entrainment coefficient decreased non-linearly in the radial direction. A new mathematical correlation was also developed to calculate the distribution of entrainment coefficient inside particle clouds. It was observed that the aspect ratio can significantly alter the radial entrainment coefficient in transverse directions. The inter-particle collision of particle clouds was evaluated by calculating the Bagnold number in both axial and radial directions. It was found that the inter-particle collision occurred for x/do ≤ 10 for St = 0.74 and for St = 0.52, and the Bagnold number values were smaller than 45 for x/do ≥ 20, indicating that a micro viscose regime controls the flow in these particle cloud dynamics.

中文翻译：

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停滞水中的粒子云动力学

摘要 进行了实验室实验以研究垂直向下释放到死水中的粒子云的动力学。以纵横比和斯托克斯数的形式研究了喷嘴直径、砂粒质量和粒度的重要性。沙粒浓度和粒子云速度的轴向和径向剖面由精确而坚固的光学探头 (PV6) 测量。开发了经验公式来解释砂浓度和速度剖面的变化。发现粒子云中的射流发展区小于单相水射流和沙射流。实验室测量还表明，与单相浮力和砂射流相比，粒子云中的中心线砂浓度下降速度较慢。在粒子云内部计算了质量、动量通量、阻力和夹带系数等重要参数，以更好地了解粒子云在死水中的演化。阻力系数的径向变化表明粒子云核心区域存在粒子群效应，阻力系数从0.4下降到小于0.1。夹带系数在径向上非线性降低。还开发了一种新的数学相关性来计算粒子云内部的夹带系数分布。据观察，纵横比可以显着改变横向的径向夹带系数。通过计算轴向和径向上的巴格诺德数来评估粒子云的粒子间碰撞。