Hydrodynamic forces on monodisperse assemblies of axisymmetric elongated particles: Orientation and voidage effects

Abstract

This work provides a recipe for creating drag, lift and torque closures for static assemblies of axisymmetric, non-spherical particles. Apart from Reynolds number Re and solids volume fraction ǫ s , we propose four additional parameters to characterize the flow through non-spherical particle assemblies. Two parameters consider the mutual orientations of particles (the orientation tensor eigenvalues S 1 and S 2 ) and two angles represent the flow direction (polar and azimuthal angles α and β). Interestingly, we observe that the hydrodynamic forces on the particles are independent of the mutual particle orientations. Rather, the most important parameter representing the particle configuration itself is the incident angle φ of the individual particles with respect to the incoming flow. Moreover, we observe that our earlier finding of sine-squared scaling of drag for isolated particles (Sanjeevi & Padding 2017) holds on average even for a multiparticle system in both the viscous and inertial regimes. Similarly, we observe that the average lift for a multiparticle system follows sine-cosine scaling, as is observed for isolated particles. Such findings are very helpful since the pressure drop of a packed bed or porous media can be computed just with the knowledge of orientation distribution of particles and their drag at φ = 0 • and φ = 90 • for a given Re and ǫ s . With the identified dependent parameters, we propose drag, lift and torque closures for multiparticle systems.

Analysis of Mobility Effects in Particle‐Gas Flows by Particle‐Resolved LBM‐DEM Simulations

“…The solids volume fraction φ is adjusted by the domain size to be either 0.2 or 0.4. The number of particles in the present work is comparable with the number of particles used in the above mentioned DNS studies investigating particle‐fluid forces in assemblies of spherical 2–11 and non‐spherical 18 particles, where it varies between 27 and 200 depending on the study.…”

“…Tab. 4 shows the deviations between the drag and lift forces computed in the PR‐DNS of spherocylinders and the respective forces obtained by the correlations of Sanjeevi and Padding 18. These correlations do not only depend on the superficial Reynolds number (Eq.…”

“…However, when considering the force magnitudes, these fluctuating force contributions do not cancel out in the ensemble average. This effect becomes less pronounced for increasing Reynolds numbers because the lift force contribution to the total particle‐fluid force becomes larger with increasing Reynolds number 18. Thus, the fluctuating force contribution in the lift force decreases.…”

“…Ratio of ensemble averaged drift force magnitude and drag force magnitude under different flow conditions: a) PR‐DNS values for spheres, b) comparison between DNS values and values predicted by the correlations of Sanjeevi and Padding 18 for cylinders and c) ratio of the two drift force components for cylinders obtained in the DNS. Note that the ratios are also time‐averaged in the case of moving particles and that the correlation prediction only contains the lift force contribution in the drift force.…”

Effect of particle orientation on the drag force in random arrays of oblate ellipsoids in low‐Reynolds‐number flows

“…Recently, for multi‐particle systems with nonspherical particles, the majority of studies are focused on investigating the drag force on elongated particles, such as prolate ellipsoids 7 and fibers 16 . Limited studies pay attention to oblate ellipsoids even if they are one of the most commonly particles in industrial applications.…”