Unsteady flow of shear-thickening fluids around an impulsively moving circular cylinder

Abstract

Unsteady flow past an impulsively moving circular cylinder in both Newtonian and shear-thickening fluids is investigated numerically. Two impulsive motions are simulated: impulsive start and impulsive stop. The Carreau viscosity model is used for shear-thickening fluids with the range of the power index 1 ≤ n ≤ 2. The Reynolds number is Re=40 base on the cylinder diameter. Simulation results of shear-thickening fluids are compared with the Newtonian case. Significant increase in the viscosity due to the impulsive motion impacts on flow features, including vortical structures, zero shear point on the cylinder surface, pressure profile, and the drag force. Current results indicate that vortical structures generated by the impulsive motion weaken and diffuse faster for a larger power index. The zero shear point on the cylinder surface is associated to the flow separation in impulsively started flow and the re-attachment in the impulsively stopped flow. The shear-thickening effect delays the separation and the re-attachment process, which is intertwined with slow development of adverse pressure gradient in shear-thickening fluids. The total drag increases as the power index increases. Contribution of the friction and the pressure drag to the total is discussed in details. The impact of the Carreau number Cu on the non-Newtonian behavior is numerically investigated as well. © 2019 Elsevier B.V.