Speaker
A Mazzino
Description
The role of polymer additives on
Rayleigh-Taylor turbulence is investigated by means of direct numerical
simulations (DNS) of Oldroyd-B viscoelastic model. The dynamics of polymer
elongations follows adiabatically the self-similar evolution of the turbulent
mixing layer and shows the appearance of a strong feedback on the flow which
originates a cut off for polymer elongations. The viscoelastic effects on the
mixing properties of the flow are twofold. Mixing is appreciably enhanced at
large scales (the mixing layer growth-rate is larger than that of the purely
Newtonian case) and depleted at small scales (thermal plumes are more coherent
with respect to the Newtonian case). The observed speed up of the thermal
plumes, together with an increase of the correlations between temperature field
and vertical velocity, contributes to a significant enhancement of heat
transport.
Our findings are consistent with a scenario of drag reduction
induced by polymers.
