Viscoplastic flow past a cylinder near a moving wall

Abstract

The flow of kaolinite mixed with water at mass fractions ≤28.5% past a cylinder near a moving wall is numerically investigated. The fluid is a non-Newtonian yield stress one and modeled as a Bingham plastic fluid. Simulations are performed at Reynolds numbers of 100≤Re≤1000 and Bingham numbers of 6.3≤Bn≤1153.1, which correspond to generalized Reynolds numbers of 0.55≤Regen≤503.6. Effects of the wall with the gap ratio varied in the range of G/D=0.1 and G/D=9 on the flow structures and the drag and lift coefficients are analyzed. The flow regime spans from laminar steady without and with boundary layer separation (and with two static unyielded zones formed at the front and rear stagnation points) to unsteady with periodic shedding of vortices behind the cylinder (and almost no unyielded zones in the near field). At small gaps, i.e., G/D≤1, both the drag and lift coefficients increase rapidly as the gap is decreased. They also increase with decreasing Regen. At G/D=9, influence of the wall is negligible, three approximations of the drag coefficient as a function of Regen are proposed.