The unsteady drag force on a cylinder immersed in a dilute granular flow

This paper presents results from hard-particle discrete element simulations of a two-dimensional dilute stream of particles accelerating past an immersed fixed cylinder. Simulation measurements of the drag force F-d are expressed in terms of a dimensionless drag coefficient, C-d=F-d/[1/2 rho nu U-2(D+d)], where rho is the particle density, nu is the upstream solid fraction, U is the upstream instantaneous velocity, and D and d are the cylinder and particle diameters, respectively. Measurements indicate that the cylinder's unsteady drag coefficient does not vary significantly from its steady (nonaccelerating) drag coefficient for both frictionless and frictional particles implying that the added mass for the flow is negligible. However, the drag coefficient is larger than its nominal value during an initial transient stage, during which a shock wave develops in front of the cylinder. Once the shock has developed, the drag coefficient remains constant despite the stream's acceleration. The duration of the shock development transient stage is a function of the number of particle/cylinder collisions. (C) 2006 American Institute of Physics.