Drag coefficients for elongated/flattened irregular particles based on particle-resolved direct numerical simulation

Drag is a fundamental force on the motion of particles. In this study, the effects of particle surface roughness, particle volume fraction, and interactions on particle drag coefficients were investigated using 3D reconstruction of particles and particle-resolved direct numerical simulation (PR-DNS). The results demonstrate that a model based on the shape parameter group, including particle sphericity, flatness ratio, and roughness parameter, could accurately explain variations in the drag coefficients of irregular particles. The impact of roughness (Sef) can be established by relating the smooth particle drag coefficient (CD,s) and the Reynolds number (Rep) to the rough particle drag coefficient (CD), which is expressed as CD = CD, s{1 + [0.0311 ln (Sef − 0.962) + 0.102]Rep0.114}. In addition, the particle flatness equation based on the maximum, intermediate and minimum projected areas of a particle can achieve a reasonable calculation of the flatness ratio throughout the full range of incidence angle. Accordingly, two new models for predicting the drag coefficients of irregular particles are proposed. The average relative errors of the models are 6.82% and 9.91%. The models are applicable to Rep range from 1 to 200, sphericity from 0.71 to 0.86, flatness ratio from 0.82 to 1.44, and particle surface roughness parameter from 1 to 1.24. Furthermore, a new drag coefficient model is correlated based on the model of Wen and Yu [1], which shows the influence of the particle volume fraction. The new shape parameter group and corrections are expected to improve the accuracy of Euler–Lagrangian simulations of uniform suspension systems comprising moderately elongated/flattened irregular particles.