Eventos Anais de eventos
ENCIT 2016
16th Brazilian Congress of Thermal Sciences and Engineering
Numerical analysis of the developing time in turbulent drag reducing plane Couette flows
Submission Author:
Anselmo Soeiro Pereira , ES
Co-Authors:
Gilmar MOMPEAN, Edson Soares
Presenter: Anselmo Soeiro Pereira
doi://10.26678/ABCM.ENCIT2016.CIT2016-0548
Abstract
The addition of a small amount of polymers of high molecular weight can lead to a pressure drop decrease in turbulent flows. Over the years, numerous studies have been conducted in attempts to make practical use of polymer-induced drag reduction: long-distance transport of liquids, oil well operations, fire-fighting, transport of suspensions and slurries, and biomedical applications. However, many aspects concerning its main mechanism are yet unclear. One of those aspects is the initial development of the turbulent structures and polymer deformation over time. As an attempt to further understand the drag reduction over this developing time, we analyse a turbulent Couette flow of a FENE-P fluid by aiding of direct numerical simulation. We show that the initial interactions between the mean shear flow, turbulent structures, and polymer stretching are the key to understand the step-by-step evolution of the drag reduction (DR). Few instants after the beginning of the simulation, DR assumes expressive negative values before starting to increase and reaches its maximum value. When DR is minimum (in fact negative), polymers experience their highest deformation state. In other words, DR and polymer stretching evolve in an asynchronous way. A point which also deserves attention is the fact that the asymptotic value of the drag reduction is below its maximum one. We propose in this work to analyse the difference between the maximum drag reduction and its asymptotic value only by means of fluid dynamics.
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