On the transition to turbulence of a viscoplastic fluid past a confined cylinder: A numerical study

Abstract

Three-dimensional direct numerical simulations of a Bingham fluid flowing past a confined circular cylinder have been used in order to investigate viscoplastic effects in the wake-transition regime. The case of a cylinder confined in a plane channel with a fixed blockage ratio (ratio of the cylinder diameter to the channel height) of 0.2 has been studied, for values of the Bingham number and Reynolds numbers (based on the cylinder diameter and bulk flow velocity) in the range 0. <. Bn≤5 and 150. ≤. Re≤. 600, respectively. The critical Reynolds number for the onset of three-dimensional flow regime has been shown to increase linearly with Bingham number, at least in the range of parameters considered. Two distinct modes of three-dimensional instability (modes A and B) have been identified in the flow, and the influence of viscoplastic effects on the evolution of these instabilities have been described. Significant deviations in the structure of the far wake from the Newtonian case have been observed and associated with a disruption of underlying processes that are known to operate in the Newtonian wake. Despite these structural differences, it has been shown that the evolution of the Strouhal number with Reynolds number in the viscoplastic fluid exhibits two discontinuous changes that are associated with the onset of the different instabilities in the flow, a behavior that mirrors the behavior in Newtonian fluids. © 2015 Elsevier Inc.