Research Fellows Directory
Professor Dwight Barkley
University of Warwick
This research concerns the turbulent motion of fluids.
We fluid flows through a pipe, channel, or duct, there are two basic forms of motion. At low speeds, the motion is smooth and the fluid moves along straight paths with little resistance. At higher speeds, the motion is typically turbulent with fluid moving along very complex whirling paths which causes much more resistance to pumping. This second situation applies to almost all cases one encounters in daily life, for example, the water flowing through the pipes in your home.
This study addresses a fundamental question, what happens as one slowly turns down the speed of fluid flowing through a pipe? How does turbulent motion at high speeds give way to smooth motion at low speeds? The answer is not that the complex motion becomes less and less complex as the speed is decreased such that eventually fluid moves along straight lines, nor is the answer that the turbulent motion abruptly terminates at some speed. Instead what occurs is a fascinating interplay of smooth and turbulent motion.
Below a well-defined speed, some regions of fluid begin to move smoothly, while most of the fluid remains fully turbulent. The smooth regions appear and disappear in a complex random way -- there arises a turbulence-within-turbulence. Significantly, this research suggests that this turbulence-within-turbulence is fundamentally responsible for maintaining complex whirling flow in the pipe at these flow speeds. Below another well-defined speed, smooth motion becomes dominant and only isolated turbulent patches exist within the flow. Such isolated patches of turbulence are thought to exist for only finite time before ultimately decaying to smooth flow.
While this research does not presently tell us how to make more efficient pipes, it addresses a fundamental connection between undesirable turbulent motion and more desirable smooth motion, and it gives us insight into what makes turbulent flow so persistent.