Article In: scopus

Turbulent entrainment in viscoelastic fluids

JOURNAL OF FLUID MECHANICS

Abreu H.; Pinho F.T.; Da Silva C.B. — 2022

Key information

Authors:

Abreu H. (Hugo Rafael Lopes Abreu); Pinho F.T.; Da Silva C.B. (Carlos Frederico Neves Bettencourt da Silva)

Published in

March 10, 2022

Abstract

Direct numerical simulations (DNS) of turbulent fronts spreading into an irrotational flow region are used to analyse the turbulent entrainment mechanism for viscoelastic fluids. The simulations use the FENE-P fluid model and are initiated from DNS of isotropic turbulence with Weissenberg and turbulence Reynolds numbers varying in the ranges 1.30≤Wi≤3.46 and 206≤Re_λ^0≤404 , respectively. The enstrophy dynamics near the turbulent/non-turbulent interface (TNTI) layer, that separates regions of turbulent and irrotational flow, includes a new mechanism – the viscoelastic production – caused by the interaction between the vorticity field and the polymer stresses. This term can be a sink or a source of enstrophy in the turbulent core region of the flow, depending on the Weissenberg number, and contributes to the initial growth of the enstrophy in the viscous superlayer, together with the viscous diffusion, which is the only mechanism present for Newtonian fluids. For low and moderate Weissenberg numbers the scaling of the TNTI layer is similar to the scaling of TNTI layers for Newtonian fluids, but this is no longer the case at high Weissenberg numbers where the enstrophy tends to be concentrated into thin vortex sheets instead of vortex tubes. Finally, it is shown that the substantial decrease of the entrainment rates observed in turbulent flows of viscoelastic fluids, compared with Newtonian fluids, is caused by a reduction of the surface area and fractal dimension of the irrotational boundary, originated by the depletion of ‘active’ scales of motion in the fluid solvent caused by the viscoelasticity.

Publication details

Authors in the community:

Title of the publication container

JOURNAL OF FLUID MECHANICS

First page or article number

31

Last page

31

Volume

934

Issue

A36

DOI

10.1017/jfm.2021.1139

Fields of Science and Technology (FOS)

mechanical-engineering - Mechanical engineering

Publication language (ISO code)

eng - English

Rights type:

Only metadata available

Financing entity

Fundação para a Ciência e a Tecnologia

Identifier for the funding entity: PCIF/GFC/0109/2017