Different industrial applications involve wide range of non-spherical particles. The present work investigates a simplified drag model that can be used for larger scale Euler-Lagrangian fluidization simulations. The flow around different prolate (needle-like) and oblate (disc-like) spheroids is studied using a multi-relaxation-time lattice Boltzmann method. We compute the mean drag coefficient CD,ϕ at different incident angles ϕ for a wide range of Reynolds numbers (Re). We show that the sine-squared drag law CD,ϕ = CD,ϕ=0∘ + (CD,ϕ=90∘−CD,ϕ=0∘)sin2ϕ holds up to large Reynolds numbers Re = 2000. The sine-squared dependence of CD occurs at Stokes flow (very low Re) due to linearity of the flow fields. We explore the physical origin behind the sine-squared law at high Re, and reveal that surprisingly, this does not occur due to linearity of flow fields. Instead, it occurs due to an interesting pattern of pressure distribution contributing to the drag, at higher Re, for different incident angles.
The present results demonstrate that it is possible to perform just two simulations at ϕ = 0∘ and ϕ = 90∘ for a given Re and obtain particle shape specific CD at arbitrary incident angles. Similarly, we find that the equivalent theoretical equation of lift coefficient CL can provide a decent approximation, even at high Re, for prolate spheroids. Such a drag and lift law valid for needle-like prolate spheroids is very useful for Euler-Lagrangian fluidization simulations of non-spherical particles. The drag law has limited applicability to flatter oblate spheroids, which do not exhibit the sine-squared interpolation, even for Re = 100, due to stronger wake-induced drag.
See more of this Group/Topical: Particle Technology Forum