A numerical investigation of fine particle laden flow in an oscillatory channel: the role of particle-induced density stratification

作者：Ozdemir Celalettin E^*; Hsu Tian Jian; Balachandar S

来源：Journal of Fluid Mechanics, 2010, 665: 1-45.

DOI：10.1017/S0022112010003769

• particle/fluid flows
• sediment transport
• stratified flows

Studying particle-laden oscillatory channel flow constitutes an important step towards understanding practical application. This study aims to take a step forward in our understanding of the role of turbulence on fine-particle transport in an oscillatory channel and the back effect of fine particles on turbulence modulation using an Eulerian-Eulerian framework. In particular, simulations presented in this study are selected to investigate wave-induced fine sediment transport processes in a typical coastal setting. Our modelling framework is based on a simplified two-way coupled formulation that is accurate for particles of small Stokes number (St). As a first step, the instantaneous particle velocity is calculated as the superposition of the local fluid velocity and the particle settling velocity while the higher-order particle inertia effect neglected. Correspondingly, only the modulation of carrier flow is due to particle-induced density stratification quantified by the bulk Richardson number, Ri. In this paper, we fixed the Reynolds number to be Re-Delta = 1000 and varied the bulk Richardson number over a range (Ri = 0, 1 x 10(-4), 3 x 10(-4) and 6 x 10(-4)). The simulation results reveal critical processes due to different degrees of the particle-turbulence interaction. Essentially, four different regimes of particle transport for the given Re-Delta are observed: (i) the regime where virtually no turbulence modulation in the case of very dilute condition, i. e. Ri similar to 0; (ii) slightly modified regime where slight turbulence attenuation is observed near the top of the oscillatory boundary layer. However, in this regime a significant change can be observed in the concentration profile with the formation of a lutocline; (iii) regime where flow laminarization occurs during the peak flow, followed by shear instability during the flow reversal. A significant reduction in the oscillatory boundary layer thickness is also observed; (iv) complete laminarization due to strong particle-induced stable density stratification.

• 出版日期2010-12