## Turbulence in dilute solutions away from solid boundaries

By: Carlos Silva

From: Dep. de Eng, Mecânica do Instituto Superior Técnico

At: C1, 1.4.14

[2021-10-21]

It is well known that when minute amounts of polymer are added into a Newtonian fluid the resulting fluid solution displays stark differences compared to a Newtonian fluid. A particularly important feature of these solutions is the very high drag reduction they are able to provide in wall bounded flows. This is related to the transfer of an important fraction of the kinetic energy of the flow into the polymer molecules, where it is stored as elastic energy. This presentation focuses on the universal aspects of this fluid-polymers interaction, and of the energy cascade process away from solid boundaries. The presentation will start by a discussion of i) the kinetic energy budgets and spectral transfer, and the shape of the energy spectrum for viscoelastic fluids at high Reynolds numbers, before addressing ii) the development of subgrid-scale closures for these flows. Finally, we will present iii) a theory for viscoelastic turbulent jets and wakes and, iv) we will describe the mechanism of turbulent entrainment for viscoelastic fluids.

This presentation discusses several features of the turbulence dynamics in polymer solutions away from solid boundaries. The topics discussed include:

i) The energy budgets and spectral transfer, and the shape of the energy spectrum at high Reynolds numbers

ii) The development of subgrid-scale closures: the distortion similarity model

iii) The turbulent entrainment in viscoelastic turbulence

iv) The theory of turbulent viscoelastic jets and wakes

**Project**UIDB/00618/2020