Numerical study of an unsteady flow of thixotropic liquids past a cylinder

Abstract

This paper presents a numerical study of a complex fluid flow past a circular cylinder. The fluid is a thixotropic viscoplastic material. Thixotropy is a time-dependent rheological property associated with the material's microstructure, which can be broken and/or built up during a flowing process. It is modeled using a structural parameter representing the structural state, which can vary from being completely broken to fully structured. Effects of the thixotropic parameters controlling the rate of the structural breakdown and recovery processes on the flow characteristics are investigated. Either the Herschel-Bulkley model or the Bingham model is employed together with Papanastasiou's regularization scheme. A review on the determination of the regularization parameter is carried out; a new approach to this is thus proposed. Various flow aspects such as the unyielded/rigid zones, the structural evolution, and the vortex structures are analyzed. Results show that at Re = 150 and Bn ≤ 5, the flow is nonstationary with periodic vortex shedding. The structural state is found to correlate well with the vortex structures. A full structural recovery can happen either within or beyond the yield boundary, or even beyond the computational domain. Moreover, the drag coefficient is reported and discussed.