Abstract
Particles are present in many natural and industrial multiphase flows. In most practical cases, particle shape is not spherical, leading to additional difficulties for numerical studies. In this paper, DNS of turbulent channel flows with finite-size prolate spheroids is performed. The geometry includes a straight wall-bounded channel at a frictional Reynolds number of 180 seeded with particles. Three different particle shapes are considered, either spheroidal (aspect ratio λ=2 or 4) or spherical (λ=1). Solid-phase volume fraction has been varied between 0.75% and 1.5%. Lattice Boltzmann method (LBM) is used to model the fluid flow. The influence of the particles on the flow field is simulated by immersed boundary method (IBM). In this Eulerian-Lagrangian framework, the trajectory of each particle is computed individually. All particle-particle and particle-fluid interactions are considered (four-way coupling). Results show that, in the range of examined volume fractions, mean fluid velocity is reduced by addition of particles. However, velocity reduction by spheroids is much lower than that by spheres; 2% and 1.6%, compared to 4.6%. Maximum streamwise velocity fluctuations are reduced by addition of particle. By comparing particle and fluid velocities, it is seen that spheroids move faster than the fluid before reaching the same speed in the channel center. Spheres, on the other hand, move slower than the fluid in the buffer layer. Close to the wall, all particle types move faster than the fluid. Moreover, prolate spheroids show a preferential orientation in the streamwise direction, which is stronger close to the wall. Far from the wall, the orientation of spheroidal particles tends to isotropy.
Highlights
Particulate suspensions are common in a wide range of industrial applications and environmental processes
We study the effect of prolate spheroids on the turbulent flow field
Lattice Boltzmann method is a promising alternative to classical CFD approaches that are based on Navier-Stokes equations
Summary
Particulate suspensions are common in a wide range of industrial applications and environmental processes. Icy clouds, biomass combustion, crystallization and pharmaceutical processes.[1,2,3] The importance and vast application of particle-laden flows necessitate proper simulation and prediction of particle-fluid interactions. Pan and Banerjee[8] used a pseudo-spectral method to model particle-laden turbulent flows in open channels with particle volume fractions of φ ∼ 10−4. Kajishima et al.[9] simulated an upward turbulent flow in a vertical channel with solid spherical particles. Uhlmann[10] simulated the motion of fully-resolved spherical particles in a vertical channel flow (φ = 4.2 × 10−3) with direct numerical
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