Variation of drag, lift and torque in a suspension of ellipsoidal particles

Previous research has mostly been focused on the drag force in fluid-particle assemblies. However, when the particle geometry is non-spherical, secondary forces and torque may no longer be negligible. In this study particle-resolved simulations are performed to study the drag force, other secondary forces, and torque in flow through a fixed random suspension of ellipsoidal particles with sphericity (Psi = 0.887). The incompressible Navier-Stokes equations are solved using the Immersed Boundary Method (IBM). The suspension of ellipsoidal particles is simulated for solid fraction between 0.1 and 0.35 using 191 to 669 particles, respectively, at low to moderate Reynolds numbers (10 <= Re <= 200). The results show that the mean drag and lift force and torque with flow incidence angle follow trends similar to that found for isolated particles. However, there are large variations in these quantities under the same conditions of Reynolds number, void fraction, and incidence angle which become more significant as the Reynolds number increases, leading to the conclusion that local flow conditions in the suspension have a large impact on forces and torques experienced by a particle. Secondary lift and lateral forces are compared to the drag force on each particle at the same Reynolds number and solid fraction. The results show that approximately 80% of particles for lift and 60% for lateral force exhibit values <10% of the drag force at low Reynolds numbers, but a significant number of particles exhibit values >10% (17% for lift and 50% for lateral force) as the Reynolds number increases, leading to the conclusion that neglecting secondary forces could lead to inaccuracies. The mean value of torque coefficient increases with void fraction and decreases with Reynolds number. However, torque on individual particles at the same mean flow conditions show large variations about the mean, even acting in the opposite direction to that indicated by the mean value. (C) 2018 Elsevier B.V. All rights reserved.