Abstract
.Particle-laden turbulent flows occur in a variety of industrial applications as well as in naturally occurring flows. While the numerical simulation of such flows has seen significant advances in recent years, it still remains a challenging problem. Many studies investigated the rheology of dense suspensions in laminar flows as well as the dynamics of point-particles in turbulence. Here we employ a fully-resolved numerical simulation based on a lattice Boltzmann scheme, to investigate turbulent flow with large neutrally buoyant particles in a pipe flow at low Reynolds number and in dilute regimes. The energy input is kept fixed resulting in a Reynolds number based on the friction velocity around 250. Two different particle radii were used giving a particle-pipe diameter ratio of 0.05 and 0.075. The number of particles is kept constant resulting in a volume fraction of 0.54% and 1.83%, respectively. We investigated Eulerian and Lagrangian statistics along with the stresslet exerted by the fluid on the spherical particles. It was observed that the high particle-to-fluid slip velocity close to the wall corresponds locally to events of high energy dissipation, which are not present in the single-phase flow. The migration of particles from the inner to the outer region of the pipe, the dependence of the stresslet on the particle radial positions and a proxy for the fragmentation rate of the particles computed using the stresslet have been investigated.Graphical abstract
Highlights
Two-phase flows dispersed with either particles or bubbles are relevant to many natural and industrial problems and under most practical conditions these flows are turbulent [1, 2]
The fact that the fragmentation rate computed from our simulations shows scaling corresponding to the HIT case for small critical values of stresslet, despite the finite-size particles and the different method to quantify to fragmentation, suggests that the microscopic mechanism causing fragmentation is consistent over a wide range of size and stress magnitude
The present work outlines a novel approach of using stresslet, computed from a finite-size representation of particles, in combination with a Direct Numerical Simulation (DNS) of turbulence to study the phenomenology of particles fragmentation in turbulent flow
Summary
Two-phase flows dispersed with either particles or bubbles are relevant to many natural and industrial problems and under most practical conditions these flows are turbulent [1, 2]. There has been some significant work using the immersed boundary method to study suspensions of finite-size particles in a turbulent channel flow for volume fractions varying up to 20%, where researchers looked into the modification of the Eulerian flow field by the dispersed phase [17,18,19], as well as the modified scaling laws in the presence of the particles [20]. In either type of fragmentation, either for particle aggregates or living cells, the phenomenology of turbulent fragmentation is still not fully understood because of the inherent complexity of the flow field along with the intricacy of the particle morphology in determining how the hydrodynamic forces redistribute over the structure of the particle and how stresses accumulate in critical locations resulting in damage or even fragmentation of particles. We will introduce a novel definition of particle circulation frequency using the time signal of the radial position of the particles
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