On the coexistence of elastic and inertial regimes in viscoelastic turbulent jets

Jets and puffs are a simplified representation of many natural, biological and industrial flows. A striking example is the puff of air exhaled by an individual; the emitted breath carries a large number of small-size droplets of biological fluid, which are all potential virus carriers. The turbulent flow in the exhaled puff determines the dispersion of these droplets; understanding of the turbulent flow allowed for scientifically-grounded prevention guidelines. In our work, we use direct numerical simulations to study the dynamics of Newtonian and non-Newtonian turbulent round jets at relatively high Reynolds number. The non-Newtonian fluid is viscoelastic and is represented using an Oldroyd-B model. We are interested in how fluid elasticity modifies the flow; to this aim we consider viscoelastic fluids having different polymer relaxation times. We will report how the non-Newtonian contribution modifies the bulk jet statistics, as for instance the centerline velocity and jet thickness, and the turbulent flow. Turbulent kinetic energy power spectra show the contribution from the polymers: a new decay rate appears in addition to the classic $-5/3$ observed in Newtonian turbulence.