Analysis of polymer drag reduction mechanisms from energy budgets

• Published in: International journal of heat and fluid flow 2013-10, Vol.43, p.52-61
• Main Authors: Thais, L., Gatski, T.B., Mompean, G.
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Computational fluid dynamics; Drag; Drag reduction; Energy budgets; Exact sciences and technology; FENE-P model; Flows in ducts, channels, nozzles, and conduits; Fluid dynamics; Fluid flow; Fundamental areas of phenomenology (including applications); Physics; Statistics; Turbulence; Turbulence control; Turbulent channel flow; Turbulent flow; Turbulent flows, convection, and heat transfer; Viscoelastic fluid
• ISSN: 0142-727X; 1879-2278
• DOI: 10.1016/j.ijheatfluidflow.2013.05.016

•Direct numerical simulation data of turbulent Newtonian and viscoelastic channel flows at high Reynolds number are produced.•A complete picture of the energy exchange between the mean, turbulent and polymeric fields is provided.•The main transfer of energy is from the turbulence to the polymer.•The amplitude of the energy transfer remains constant between low and high drag reduction regimes. The transfer of energy in drag reducing viscoelastic flows is analyzed through a sequence of energetic budgets that include the mean and turbulent kinetic energy, and the mean polymeric energy and mean elastic potential energy. Within the context of single-point statistics, this provides a complete picture of the energy exchange between the mean, turbulent and polymeric fields. The analysis utilizes direct simulation data of a fully developed channel flow at a moderately high friction Reynolds number of 1000 and at medium (30%) and high (58%) drag reduction levels using a FENE-P polymeric model. Results show that the primary effect of the interaction between the turbulent and polymeric fields is to transfer energy from the turbulence to the polymer, and that the magnitude of this transfer does not change between the low and high drag reduction flows. This one-way transfer, with an amplitude independent of the drag reduction regime, comes in contradiction with the purely elastic coupling which is implicit within the elastic theory of the polymer drag reduction phenomenon by Tabor and De Gennes (Europhys. Lett. 2, pp. 519–522, 1986).