No abstract

We study the flow past a finite-length yawed 3D cylinder by a Finite Volume / Fictitious Domain (FV/FD) method developed in [63]. We validate our non-boundary-fitted method against boundary-fitted numerical results for a finite-length cylinder whose axis is parallel to the streamwise direction. Drag and lift forces exerted on the cylinder and vortex shedding onset and frequency are carefully analysed. Satisfactory agreement with published results give strong confidence in the numerical methodology provided the boundary layer is accurately resolved. Then, we carry out a detailed study of the flow past a yawed cylinder of aspect ratio L/D = 3 (where L is the cylinder length and D is the cylinder diameter) at moderate Reynolds numbers (25 Re 250). We show that the wake pattern depends strongly on Re and the yaw angle θ with respect to the streamwise direction. Various regimes are encountered including standing-eddy pattern, steady shedding of one and two pairs of counter-rotating vortices, periodic shedding of two pairs of counter-rotating vortices and unsteady shedding of hairpin shaped vortices. The standing-eddy pattern regime shows different forms of behaviour and symmetry as function of θ. Hydrodynamic forces exerted on the cylinder are well approximated by laws derived in the Stokes flow regime (benefitting from the linearity of the equations), even for moderate Reynolds numbers. This result is in agreement with recent findings of Sanjeevi and Padding [53] who studied the flow past spheroidal particles.For the highest Reynolds numbers (Re = 150, 200, 250) we show that simple force laws can be derived from simple geometrical assumptions. These simple laws yield a satisfactory match with our numerical results.

Micro/meso simulation of a fluidized bed in a homogeneous bubbling regime, International Journal of Multiphase Flow, 92, 93-111, we performed a one-to-one comparison of micro-scale Particle-Resolved Simulation (PRS) results and meso-scale two-way coupled Euler-Lagrange (a. k. a. DEM-CFD for Discrete Element Method-Computational Fluid Dynamics) simulation results in a homogeneous bi-periodic liquid/solid fluidized bed. These data showed an acceptable agreement between micro-and meso-scale predictions for integral measures as, e.g., pressure drop and bed height. However, particles fluctuations are markedly underpredicted in DEM-CFD simulations, especially in the direction transverse to the main flow.

The present work studies particle resolved simulations of liquid/solid and gas/solid fluidization in a cuboid domain with periodic lateral boundary conditions. The focus is on investigating particles’ dynamics, while a particular care is devoted to the spatial grid resolution and statistical time convergence of the results. A statistical analysis of particles’ motion and fluid fluctuations asserts the intrinsic differences in the flow characteristics and mixing properties of these two configurations. Results reveal anisotropic mechanisms driving particles’ motion and highlight the dominance of diffusive and convective mechanisms in liquid/solid and gas/solid regimes, respectively. Following a framework similar to that of Nicolai et al. [“Particle velocity fluctuations and hydrodynamic self-diffusion of sedimenting non-Brownian spheres,” Phys. Fluids 7(1), 12–23 (1995)], we estimate the correlation time and the fluctuation length of particles’ motion. A force budget analysis is discussed to gain more insight into the role of collision in isotropization of the system. Owing to the wide range of employed grid resolutions and accurate error analysis, the present dataset is also deemed to be useful in calibrating the grid resolution for a desired accuracy of the solution in a fluidization configuration.