A direct numerical investigation of two-way interactions in a particle-laden turbulent channel flow

Abstract

Understanding the two-way interactions between finite-size solid particles and a wall-bounded turbulent flow is crucial in a variety of natural and engineering applications. Previous experimental measurements and particle-resolved direct numerical simulations revealed some interesting phenomena related to particle distribution and turbulence modulation, but their in-depth analyses are largely missing. In this study, turbulent channel flows laden with neutrally buoyant finite-size spherical particles are simulated using the lattice Boltzmann method. Two particle sizes are considered, with diameters equal to 14.45 and 28.9 wall units. To understand the roles played by the particle rotation, two additional simulations with the same particle sizes but no particle rotation are also presented for comparison. Particles of both sizes are found to form clusters. Under the Stokes lubrication corrections, small particles are found to have a stronger preference to form clusters, and their clusters orientate more in the streamwise direction. As a result, small particles reduce the mean flow velocity less than large particles. Particles are also found to result in a more homogeneous distribution of turbulent kinetic energy (TKE) in the wall-normal direction, as well as a more isotropic distribution of TKE among different spatial directions. To understand these turbulence modulation phenomena, we analyse in detail the total and component-wise volume-averaged budget equations of TKE with the simulation data. This budget analysis reveals several mechanisms through which the particles modulate local and global TKE in the particle-laden turbulent channel flow.

Flow modulation by a few fixed spherical particles in a turbulent channel flow

“…In the work of Vreman & Kuerten (2018), particles were placed near the channel centre. However, according to the previous studies of turbulent channel flows laden with freely moving particles (see, e.g., Shao et al (2012), Picano et al (2015), Eshghinejadfard et al (2017) and Peng, Ayala & Wang (2019b)), the most intensive flow modulation happens in the near-wall regions. The particle configuration adopted by Vreman & Kuerten (2018) may bring some difficulty to the assessment of how the modulation effects brought by particles interact with the near-wall turbulence.…”

“…Lubrication models are needed to deal with the unresolved short-range hydrodynamic interactions. However, the selection of a lubrication model and its numerical effects on the observations of flow modulation are yet to be fully understood (see Peng et al 2019b). The second issue is the insufficient local grid resolution near the wall when particles can move freely.…”

“…Since particles can slip on the channel wall while fluid cannot, freely moving particles appearing in the near-wall region may create large local velocity gradients that require very fine grid resolutions to resolve, which were not usually affordable. In the reported TKE budget analyses with every term explicitly computed, the errors were beyond 10 % (see Santarelli et al 2016;Peng & Wang 2019;Peng et al 2019b). This level of error complicates reliable quantitative analyses of the results.…”

Statistics of temperature and thermal energy dissipation rate in low-Prandtl number turbulent thermal convection

“…One is that LB method is easy to be implemented and parallelized, benefiting from its local nonlinearity, while the other is that LB method has lower numerical dissipation compared to conventional second-order computational fluid dynamics methods [24][25][26] . During the past several decades, the LB method has been successfully applied to DNS of turbulent flows, including decaying homogeneous isotropic turbulence 27,28 , turbulent channel and pipe flows 29,30 , and turbulent thermal convective flows 31 .…”

Collision-induced breakage of agglomerates in homogenous isotropic turbulence laden with adhesive particles

“…It may not hold for particles that are considerably larger than the Kolmogorov scale. In the latter case, particle-resolved simulations would be needed to precisely calculate the flow around and forces on particles (Ernst, Dietzel & Sommerfeld 2013; Liu & Wu 2019; Peng, Ayala & Wang 2019; Wang et al 2019).…”