title: Simple framework for understanding the universality of the maximum drag reduction asymptote in turbulent flow of polymer solutions.
abstract: Self-consistent direct numerical simulations of turbulent channel flows of dilute polymer solutions exhibiting friction drag reduction (DR) show that an effective Deborah number defined as the ratio of polymer relaxation time to the time scale of fluctuations in the vorticity in the mean flow direction remains O(1) from the onset of DR to the maximum drag reduction (MDR) asymptote. However, the ratio of the convective time scale associated with streamwise vorticity fluctuations to the vortex rotation time decreases with increasing DR, and the maximum drag reduction asymptote is achieved when these two time scales become nearly equal. Based on these observations, a simple framework is proposed that adequately describes the influence of polymer additives on the extent of DR from the onset of DR to MDR as well as the universality of the MDR in wall-bounded turbulent flows with polymer additives.
authors.affiliation: School of Energy and Power Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, People's Republic of China.|Materials Research and Innovation Laboratory, Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: Chang-Feng
authors.initials: CF
authors.lastname: Li
authors.affiliation: Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, New York 13244, USA.
authors.forename: Radhakrishna
authors.initials: R
authors.lastname: Sureshkumar
authors.affiliation: Materials Research and Innovation Laboratory, Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: Bamin
authors.initials: B
authors.lastname: Khomami
mesh_terms: D017276:Friction; D057446:Hydrodynamics; D011108:Polymers / Q000737:chemistry*; D012212:Rheology; D012399:Rotation; D012996:Solutions
chemical_list: D011108:Polymers; D012996:Solutions