Dynamic coefficient of friction and granular drag force in dense particle flows: Experiments and DEM simulations

The vertical granular drag force on objects held stationary in a moving bed of nickel pellets with diameters in the range 1–10mm has been measured and compared with Discrete Element Method (DEM) simulations. Experiments were carried out with horizontal wooden rods, and horizontal and vertical thin plates made of mild steel or Teflon. The experimental data are correlated by semi-empirical equations based on the “supported mass” of pellets in the region above the object, and dynamic friction coefficients acting on vertical surfaces from least-squares regression. Dynamic coefficients of friction for nickel on steel and nickel on Teflon are reported. The correlation is compared with an expression based on Janssen's equation using the experimentally determined coefficients of friction. These results are compared with DEM simulations, which examine the effects of particle size distribution, mass flow rate, plate friction coefficient μ and the simulation parameter K1, which is analogous to a spring constant. The correlation follows the trends of the data and the DEM results agree well with the experimental data over a wide range of conditions. The DEM simulations were carried out on Graphics Processing Units (GPU) that enabled a speed-up factor of ~40, and some aspects of the implementation on GPUs are discussed.