Elastoviscoplastic fluid flow past a circular cylinder
Abstract
The combined effect of fluid elasticity and yield-stress on the flow past a circular cylinder is studied by two-dimensional direct numerical simulation. We analyze the effects of yield-stress, elasticity, shear-thinning, and shear-thickening on the wake characteristics using the Saramito constitutive model. The elastoviscoplastic (EVP) wake flow is studied at a moderate Reynolds number (Re = 100) where two-dimensional vortex shedding occurs in the Newtonian case. We find that in the shear-thinning elastoviscoplastic flow, when yield stress increases, the drag coefficient and root mean square of the lift coefficient both decrease, while the length of the recirculation bubble LRB increases. These changes indicate that the wake oscillation amplitude decreases with an increasing yield stress. For shear-thickening however, the drag coefficient CD increases at a large Bingham number, and the wake becomes chaotic. The comparison of viscoelastic fluid and EVP fluid reveals that the polymer stresses, tr(τp), decay considerably less downstream of the cylinder in the EVP case, indicating that significant stresses persist at large distances. We observe that shear-thinning competes with elastic and yield stresses and counteracts their effect, while shear-thickening enhances elastic and yield stress effects, so that the flow pattern can change from periodic to a chaotic flow.