Exeptionnal seminar: Carlo Massimo Casciola (Sapienza University of Rome)

It has been known since the forties that a minuscule amount of long-chain polymers can achieve an enormous reduction of turbulent drag. This is the so-called Toms’ effect, exploited to reduce the cost of transporting oil through the trans-Alaskan pipeline or to increase the range of firemen's hoses. A long time elapsed before numerical simulation could attempt to partially shed light on the nature of the process, exploiting an effective description of viscoelastic fluids, the so-called FENE-P model. Recently, we proposed a new approach, where the single polymer chains are transported by the otherwise Newtonian fluid exchanging a backreaction force on the turbulent solvent. This model can account for the actual physicochemical properties of the real polymer molecules and, thanks to the computational power of the current GPU-accelerated, highly parallel supercomputers, allows simulating the realistic behavior of the turbulent polymer suspension, at, or close to, the actual experimental conditions. The talk will preliminarily illustrate the polymer model and describe the algorithm (ERPP - Exact Regularized Point Particle method) used to compute the polymer backreaction. The discussion will focus on the physical nature of the polymer response by showing novel numerical results at a large polymer concentration and Reynolds number. The issue of dumbbells vs multi-bead chains will be addressed, and, depending on time availability, it will be touched upon the subject of drag reduction by surfactant micelles, which can break and reform under the action of the turbulent shear.

References:
- F. Serafini, F. Battista, P. Gualtieri, and C.M. Casciola, “Polymers in turbulence: any better than dumbbells?”, Journal of Fluid Mechanics, 2024, to appear.
- F. Serafini, F. Battista, P. Gualtieri, and C.M. Casciola, “Kinetic energy budget in turbulent flows of dilute polymer solutions”, Flow, Turbulence, and Combustion, 2024.
- F. Serafini, F. Battista, P. Gualtieri, and C.M. Casciola, “The role of polymer parameters and configurations in dragreduced turbulent wall-bounded flows: comparison between FENE and FENE-P”, International Journal of Multiphase Flows, 2023.
- F. Serafini, F. Battista, P. Gualtieri, and C.M. Casciola, “Drag Reduction in Polymer-Laden Turbulent Pipe Flow”, Physics of Fluids, 2022.
- F. Serafini, F. Battista, P. Gualtieri, and C.M. Casciola, “Drag reduction in turbulent wall-bounded flows of realistic polymer solutions”, Physical Review Letters, 2022.

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