Experiments in Hibernating Turbulence
Abstract
Recent studies have revealed that turbulence appears to be organized around underlying structures in state space that correspond to specific time-dependent patterns in physical space. Some of these patterns exhibit very low drag, and their appearance can be promoted in principle to achieve skin friction reduction. One very successful approach to reduction of skin friction, albeit only in liquids, is to add small amounts of additives such as longchain linear polymers. These non-Newtonian polymer solutions display a so-called "maximum drag reduction" (MDR) phenomenon, at which very large levels of drag reduction are found, and the mean velocity profile has a universal form known as the Virk asymptote. Recent work from the collaborator s group (Graham) has brought together these observations and, using computations at low Reynolds number in a minimal channel flow geometry, discovered that even in Newtonian flow there exist transient low drag periods (denoted "hibernating turbulence") very much like those found at high levels of drag reduction in polymer solutions. Working in collaboration with the Graham group, the PI s group has produced the first experimental observations of such hibernating turbulent events performed using a conditional sampling approach devised by the PI and collaborator Graham to show unequivocally that the MDR profile is found transiently in Newtonian channel flow. This collaborative experimental work unambiguously shows that the signature of drag reduction in polymer solutions is present transiently in Newtonian flow, giving impetus to the idea that it can be exploited to promote skin friction reduction.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 23, 2016
- Source ID
- FA95501610076
Entities
People
- Robert J Poole
Organizations
- Air Force Office of Scientific Research
- United States Air Force
- University of Liverpool