Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session E27: Turbulence: Polymers/Drag Reduction |
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Chair: Vincent Terrapon, University of Liege Room: 2009 |
Sunday, November 23, 2014 4:45PM - 4:58PM |
E27.00001: Turbulence scalings in pipe flows exhibiting polymer-induced drag reduction Ivan Zadrazil, Christos Markides Non-intrusive laser based diagnostics technique, namely Particle Image Velocimetry, was used to in detail characterise polymer induced drag reduction in a turbulent pipe flow. The effect of polymer additives was investigated in a pneumatically-driven flow facility featuring a horizontal pipe test section of inner diameter 25.3 mm and length 8 m. Three high molecular weight polymers (2, 4 and 8 MDa) at concentrations of 5 -- 250 wppm were used at Reynolds numbers from 35000 to 210000. The PIV derived results show that the level of drag reduction scales with different normalised turbulence parameters, e.g. streamwise and spanwise velocity fluctuations, vorticity or Reynolds stresses. These scalings are dependent of the distance from the wall, however, are independent of the Reynolds numbers range investigated. [Preview Abstract] |
Sunday, November 23, 2014 4:58PM - 5:11PM |
E27.00002: Tampering with the turbulent energy cascade with polymer additives Pedro Valente, Carlos da Silva, Fernando Pinho We show that the strong depletion of the viscous dissipation in homogeneous viscoelastic turbulence reported by previous authors does not necessarily imply a depletion of the turbulent energy cascade. However, for large polymer relaxation times there is an onset of a polymer-induced kinetic energy cascade which competes with the non-linear energy cascade leading to its depletion. Remarkably, the total energy cascade flux from both cascade mechanisms remains approximately the same fraction of the kinetic energy over the turnover time as the non-linear energy cascade flux in Newtonian turbulence. [Preview Abstract] |
Sunday, November 23, 2014 5:11PM - 5:24PM |
E27.00003: On the connection between Maximum Drag Reduction and Newtonian fluid flow Richard Whalley, Jae-Sung Park, Anubhav Kushwaha, David Dennis, Michael Graham, Robert Poole To date, the most successful turbulence control technique is the dissolution of certain rheology-modifying additives in liquid flows, which results in a universal maximum drag reduction (MDR) asymptote. The MDR asymptote is a well-known phenomenon in the turbulent flow of complex fluids; yet recent direct numerical simulations of Newtonian fluid flow have identified time intervals showing key features of MDR. These intervals have been termed ``hibernating turbulence'' and are a weak turbulence state which is characterised by low wall-shear stress and weak vortical flow structures. Here, in this experimental investigation, we monitor the instantaneous wall-shear stress in a fully-developed turbulent channel flow of a Newtonian fluid with a hot-film probe whilst simultaneously measuring the streamwise velocity at various distances above the wall with laser Doppler velocimetry. We show, by conditionally sampling the streamwise velocity during low wall-shear stress events, that the MDR velocity profile is approached in an additive-free, Newtonian fluid flow. This result corroborates recent numerical investigations, which suggest that the MDR asymptote in polymer solutions is closely connected to weak, transient Newtonian flow structures. [Preview Abstract] |
Sunday, November 23, 2014 5:24PM - 5:37PM |
E27.00004: ABSTRACT WITHDRAWN |
Sunday, November 23, 2014 5:37PM - 5:50PM |
E27.00005: Multi-scale study on process of contravariant and covariant polymer elongation and drag reduction in viscoelastic turbulence Kiyosi Horiuti, Shu Suzuki We study the elongation process of polymers released in the Newtonian homogeneous isotropic turbulence by connecting a mesoscopic description of ensemble of elastic dumbbells using Brownian dynamics (BDS) to the macroscopic description for the fluid using DNS. The dumbbells are allowed to be advected non-affinely with the macroscopically-imposed deformation. More drastic drag reduction is achieved when non-affinity is maximum than in the complete affine case. In the former case, the dumbbell is convected as a covariant vector, and in the latter as a contravariant vector. We derive the exact solution for the governing equation of the motion of dumbbells. The maximum stretching of dumbbell is achieved when the dumbbell aligns in the direction of vorticity in the contravariant case, and when the dumbbell directs outward perpendicularly on the vortex sheet in the covariant case. Alignment in the BDS-DNS data agrees with the theoretical results. In the mixture of contravariant and covariant dumbbells, the covariant dumbbells are transversely aligned with the contravariant dumbbells. Compared with the cases without mixture, stretching of covariant dumbbell is enhanced, while that of contravariant dumbbell is reduced. Application of this phenomenon is discussed. [Preview Abstract] |
Sunday, November 23, 2014 5:50PM - 6:03PM |
E27.00006: Breakup of colloidal aggregates in turbulent channel flow Alfredo Soldati, Cristian Marchioli Breakup of small aggregates in turbulence is of high relevance to industrial applications (from processing of colloids and nanomaterials to flocculation) and environmental processes (marine snow formation). In spite of their importance, breakup phenomena are poorly understood from a fundamental viewpoint and a basic description of breakup dynamics is still lacking. In this work we examine the complex role of turbulence and the way it generates fluctuating hydrodynamic stresses to which an aggregate is exposed. We use pseudo-spectral DNS and Lagrangian tracking to determine the breakup rate of sub-Kolmogorov colloidal massless aggregates in non-homogeneous anisotropic turbulence, considering both instantaneous and ductile breakup. Instantaneous breakup occurs when the stress generated by the surrounding fluid exceeds the critical value required to break that aggregate: $\sigma > \sigma_{cr}$. Ductile breakup is consequence of a non-instantaneous process activated when $\sigma > \sigma_{cr}$ and occurs when the energy dissipated by the surrounding fluid, $E=\int \epsilon(\tau|\sigma > \sigma_{cr})$d$\tau$ with $\epsilon$ the fluid kinetic energy dissipation rate and $\tau$ time, exceeds the critical breakup value. Effects on breakup rates due to aggregate inertia will also be discussed. [Preview Abstract] |
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