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Turbulent Drag Reduction by a Near Wall Surface Tension Active Interface

In this work we study the turbulence modulation in a viscosity-stratified two-phase flow using Direct Numerical Simulation (DNS) of turbulence and the Phase Field Method (PFM) to simulate the interfacial phenomena. Specifically we consider the case of two immiscible fluid layers driven in a closed r...

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Autores principales: Ahmadi, Somayeh, Roccon, Alessio, Zonta, Francesco, Soldati, Alfredo
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Springer Netherlands 2018
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6044243/
https://www.ncbi.nlm.nih.gov/pubmed/30069147
http://dx.doi.org/10.1007/s10494-018-9918-2
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author Ahmadi, Somayeh
Roccon, Alessio
Zonta, Francesco
Soldati, Alfredo
author_facet Ahmadi, Somayeh
Roccon, Alessio
Zonta, Francesco
Soldati, Alfredo
author_sort Ahmadi, Somayeh
collection PubMed
description In this work we study the turbulence modulation in a viscosity-stratified two-phase flow using Direct Numerical Simulation (DNS) of turbulence and the Phase Field Method (PFM) to simulate the interfacial phenomena. Specifically we consider the case of two immiscible fluid layers driven in a closed rectangular channel by an imposed mean pressure gradient. The present problem, which may mimic the behaviour of an oil flowing under a thin layer of different oil, thickness ratio h(2)/h(1) = 9, is described by three main flow parameters: the shear Reynolds number Re(τ) (which quantifies the importance of inertia compared to viscous effects), the Weber number We (which quantifies surface tension effects) and the viscosity ratio λ = ν(1)/ν(2) between the two fluids. For this first study, the density ratio of the two fluid layers is the same (ρ(2) = ρ(1)), we keep Re(τ) and We constant, but we consider three different values for the viscosity ratio: λ = 1, λ = 0.875 and λ = 0.75. Compared to a single phase flow at the same shear Reynolds number (Re(τ) = 100), in the two phase flow case we observe a decrease of the wall-shear stress and a strong turbulence modulation in particular in the proximity of the interface. Interestingly, we observe that the modulation of turbulence by the liquid-liquid interface extends up to the top wall (i.e. the closest to the interface) and produces local shear stress inversions and flow recirculation regions. The observed results depend primarily on the interface deformability and on the viscosity ratio between the two fluids (λ).
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spelling pubmed-60442432018-07-30 Turbulent Drag Reduction by a Near Wall Surface Tension Active Interface Ahmadi, Somayeh Roccon, Alessio Zonta, Francesco Soldati, Alfredo Flow Turbul Combust Article In this work we study the turbulence modulation in a viscosity-stratified two-phase flow using Direct Numerical Simulation (DNS) of turbulence and the Phase Field Method (PFM) to simulate the interfacial phenomena. Specifically we consider the case of two immiscible fluid layers driven in a closed rectangular channel by an imposed mean pressure gradient. The present problem, which may mimic the behaviour of an oil flowing under a thin layer of different oil, thickness ratio h(2)/h(1) = 9, is described by three main flow parameters: the shear Reynolds number Re(τ) (which quantifies the importance of inertia compared to viscous effects), the Weber number We (which quantifies surface tension effects) and the viscosity ratio λ = ν(1)/ν(2) between the two fluids. For this first study, the density ratio of the two fluid layers is the same (ρ(2) = ρ(1)), we keep Re(τ) and We constant, but we consider three different values for the viscosity ratio: λ = 1, λ = 0.875 and λ = 0.75. Compared to a single phase flow at the same shear Reynolds number (Re(τ) = 100), in the two phase flow case we observe a decrease of the wall-shear stress and a strong turbulence modulation in particular in the proximity of the interface. Interestingly, we observe that the modulation of turbulence by the liquid-liquid interface extends up to the top wall (i.e. the closest to the interface) and produces local shear stress inversions and flow recirculation regions. The observed results depend primarily on the interface deformability and on the viscosity ratio between the two fluids (λ). Springer Netherlands 2018-04-25 2018 /pmc/articles/PMC6044243/ /pubmed/30069147 http://dx.doi.org/10.1007/s10494-018-9918-2 Text en © The Author(s) 2018 Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
spellingShingle Article
Ahmadi, Somayeh
Roccon, Alessio
Zonta, Francesco
Soldati, Alfredo
Turbulent Drag Reduction by a Near Wall Surface Tension Active Interface
title Turbulent Drag Reduction by a Near Wall Surface Tension Active Interface
title_full Turbulent Drag Reduction by a Near Wall Surface Tension Active Interface
title_fullStr Turbulent Drag Reduction by a Near Wall Surface Tension Active Interface
title_full_unstemmed Turbulent Drag Reduction by a Near Wall Surface Tension Active Interface
title_short Turbulent Drag Reduction by a Near Wall Surface Tension Active Interface
title_sort turbulent drag reduction by a near wall surface tension active interface
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6044243/
https://www.ncbi.nlm.nih.gov/pubmed/30069147
http://dx.doi.org/10.1007/s10494-018-9918-2
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