On the transition between turbulence regimes in particle-laden channel flows

Abstract

Turbulent wall-bounded flows exhibit a wide range of regimes with significant interaction between scales. The fluid dynamics associated with single-phase channel flows is predominantly characterized by the Reynolds number. Meanwhile, vastly different behaviour exists in particle-laden channel flows, even at a fixed Reynolds number. Vertical turbulent channel flows seeded with a low concentration of inertial particles are known to exhibit segregation in the particle distribution without significant modification to the underlying turbulent kinetic energy (TKE). At moderate (but still low) concentrations, enhancement or attenuation of fluid-phase TKE results from increased dissipation and wakes past individual particles. Recent studies have shown that denser suspensions significantly alter the two-phase dynamics, where the majority of TKE is generated by interphase coupling (i.e. drag) between the carrier gas and clusters of particles that fall near the channel wall. In the present study, a series of simulations of vertical particle-laden channel flows with increasing mass loading is conducted to analyse the transition from the dilute limit where classical mean-shear production is primarily responsible for generating fluid-phase TKE to high-mass-loading suspensions dominated by drag production. Eulerian–Lagrangian simulations are performed for a wide range of particle loadings at two values of the Stokes number, and the corresponding two-phase energy balances are reported to identify the mechanisms responsible for the observed transition.

Two mechanisms of modulation of very-large-scale motions by inertial particles in open channel flow

“…In particle-laden flow, Richter (2015) finds that the particle-induced, Stokes-numberdependent source/sink of TKE varies with wavelength, and is possibly associated with the particle clusters themselves (Capecelatro et al 2018). Focusing exclusively on the inner region, Wang & Richter (2019) find that low inertia particles enhance LSMs whereas high inertia particles attenuate LSMs, which can help explain the positive particle feedbackΨ 11 for case2 ( figure 13(b)) but negative for case5 ( figure 13(e)).…”

“…There has been substantial progress in understanding inertial particle dynamics in the inner layer (i.e. related to LSMs), for instance the phenomena of particle clustering and segregation (Pan & Banerjee 1995;Marchioli & Soldati 2002;Sardina et al 2012), drag reduction (Dritselis & Vlachos 2008), high particle loading and cluster dynamics (Capecelatro et al 2018), particle inducing upscale energy transfer and transportation (Richter 2015), and regeneration cycle modulation (Wang & Richter 2019). However to the best of our knowledge, very little attention has been paid to particle clustering and modulation of VLSMs in the outer layer.…”

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

“…Gualtieri et al (2015); Horwitz & Mani (2016); Ireland & Desjardins (2017). Investigations of particleladen turbulent flows in the two-way coupling regime are found in Vreman et al (2009);Capecelatro et al (2018).…”

Inertial particle velocity and distribution in vertical turbulent channel flow: A numerical and experimental comparison

“…The particle/wall collisions also affect the particle-induced turbulence modulation [49]. In addition, particles at high mass loading tend to decrease the thickness of the boundary layer and increase the skin friction [50], and act as the primary source of turbulence generation [8,9].…”