The effects of polymer / surfactant additives on the flow and heat transfer around a circular cylinder in periodic vortex shedding

Abstract

This study focuses on the flow and heat transfer properties of dilute poly mer/surfactant solutions using Newtonian, and inelastic/elastic non-Newtonian con stitutive models. The results are discussed in terms of drag and lift coefficients, vortex shedding frequency, vortex formation length, separation angle, the critical Reynolds number for the onset of vortex shedding, local and average Nusselt numbers. Drag re duction is observed for shear thinning fluids; moreover, the vortex shedding frequency increases, and the vortex formation length decreases under shear thinning. Fluid elas ticity leads to an increase in the drag coefficient and vortex formation length, and a decrease in the vortex shedding frequency and separation angle. The onset of vortex shedding is earlier under shear thinning whereas it is delayed under shear thickening. It is also observed that weakly elastic effects have almost no impact on the onset of peri odic vortex shedding. Blockage effect causes to increase time-averaged drag coefficient and Strouhal number and it delays the onset of laminar vortex shedding for Newtonian and shear thickening fluids. For non-isothermal flow condition, heat transfer enhance ment is observed under inelastic shear thinning effects through an increase of the local and average Nusselt numbers, however purely viscoelastic effects lead to a decrease in the rate of convective heat transfer for the studied range of parameters. Temperature gradients decrease in the wake region under elasticity whereas shear thinning leads to an increase in the gradients and to the formation of elongated and clustered isotherms.