Elastoviscoplastic flows past a cylinder: Fluid-mechanical aspects and dynamic mode decomposition analysis

Abstract

When undergoing deformation, elastoviscoplastic fluids exhibit simultaneous viscous, elastic, and plastic characteristics. This study presents an extensive numerical investigation into how the combined elasticity and plasticity of such fluids influence the flow dynamics past a circular cylinder in the laminar vortex-shedding regime. By varying dimensionless numbers, such as the Weissenberg and Bingham numbers, this study elucidates their effects on various fluid-mechanical aspects, including streamlines, vorticity, drag and lift forces, and vortex-shedding frequency. The results show significant differences in the vortex street length, width, and shedding frequency downstream of the cylinder when both fluid elasticity and plasticity are present, compared to Newtonian fluids or fluids with only elasticity under the same flow conditions. Notably, flow field fluctuations are suppressed as fluid elasticity increases, an effect further accentuated by the introduction of fluid plasticity. These rheological behaviors also have a pronounced effect on the drag and lift forces acting on the cylinder. In particular, the drag forces increase with the Weissenberg and Bingham numbers while lift forces decrease. Furthermore, this study conducts the dynamic mode decomposition (DMD) analysis, a widely used reduced order modeling technique, to obtain insights into the coherent flow structures associated with the time-resolved vorticity fields for various fluids. This analysis uncovers hidden differences in the downstream vorticity structures of various fluid types using only a few DMD modes, differences that are not apparent from simple vorticity plots alone. Overall, the findings of this study are valuable for manipulating fluid-dynamical aspects, particularly the vortex-shedding phenomenon from bluff bodies, which is observed in many practical applications and natural processes.