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# Elastoviscoplastic fluid flow past a circular cylinder

Mar 2023

The combined effect of fluid elasticity and yield-stress on the flow past acircular cylinder is studied by two-dimensional direct numerical simulation. Weanalyze the effects of yield-stress, elasticity, shear-thinning, andshear-thickening on the wake characteristics using the Saramito constitutivemodel. The elastoviscoplastic (EVP) wake flow is studied at a moderate Reynoldsnumber (Re = 100) where two-dimensional vortex shedding occurs in the Newtoniancase. We find that in the shear-thinning elastoviscoplastic flow, when yieldstress increases, the drag coefficient and root mean square of the liftcoefficient both decrease, while the length of the recirculation bubble$L_{RB}$ increases. These changes indicate that the wake oscillation amplitudedecreases with an increasing yield stress. For shear-thickening however, thedrag coefficient $C_D$ increases at a large Bingham number, and the wakebecomes chaotic. The comparison of viscoelastic fluid and EVP fluid revealsthat the polymer stresses, tr($\tau^p$), decay considerably less downstream ofthe cylinder in the EVP case, indicating that significant stresses persist atlarge distances. We observe that shear-thinning competes with elastic and yieldstresses and counteracts their effect, while shear-thickening enhances elasticand yield stress effects, so that the flow pattern can change from periodic toa chaotic flow.

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