Turbulent energy routes in viscoelastic wall turbulence

Abstract

A small amount of long chain polymers dissolved in an otherwise Newtonian flow is known to reduce dramatically drag in wall bounded flows. This corresponds to a drastic change in the mean velocity profile, where the slope of the log-law in the near wall region passes from 2.5 to 11.7, see Virk (1975). This phenomenon is the most reported of a thorough alteration of the dynamics of wall turbulence, but it is still lacking a satisfactory esplanation. To advance in this direction, in the present contribution we will extend the scale by scale analysis of a viscoelastic channel flow already presented in our previous paper in Palma & Lopes (2007) discussing the alteration of the energy fluxes from production to Newtonian and non-Newtonian dissipation. The proposed framework, which had been used by Marati et al. (2004) and recently applied to larger Reynolds number Newtonian turbulence, Cimarelli et al. (2011), simultaneously describes the dynamics of turbulent fluctuations in the space of scales and in the physical space, and can be used to understand the alteration of the mechanisms of formation and sustainment of the turbulent fluctuations in the near-wall region.