1 October: CPF Seminar

Published in the Research School of Physics Event Horizon
Vol44 Issue39 30 September–4 October 2019

CPF Seminar

1 October Tuesday

11:00 am

Huxley Teaching H4.20

Dr. Rory Cerbus,

Okinawa Institute of Science and Technology, Japan

Title: Friction and fluctuations in transitional pipe flow

Abstract:

Pipe flow is laminar at low flow velocities and turbulent at high flow velocities. At intermediate velocities there is a transition wherein plugs of laminar flow alternate along the pipe with ``flashes" of a type of fluctuating, non-laminar flow which continue to be the object of intense study. Here we address two properties of flashes: friction and fluctuations. In the 19th century, Osborne Reynolds, who first reported flashes, sought to connect them with quantitative ``laws of resistance" whereby the fluid friction is determined as a function of the Reynolds number. While he succeeded for laminar and turbulent flows, the laws for transitional flows eluded him and remain unknown to this day. In seemingly unrelated work, A.N. Kolmogorov predicted that all turbulent flows are the same at small scales: the property of ‘small-scale universality’. Based on the restrictive assumptions invoked by Kolmogorov to demonstrate this universality, it is widely thought that only idealized turbulent flows conform to this framework. Using experiments and simulations that span a wide range of Reynolds number and by properly distinguishing between flashes and laminar plugs in the transitional regime, we uncover the law of resistance for flashes and demonstrate for the first time that small-scale universality holds even in low Reynolds number, inhomogeneous, unsteady transitional pipe flow.

Dr. Rory Cerbus is a Staff Scientist in the Fluid Mechanics Unit at the Okinawa Institute of Science and Technology (OIST) in Japan. Rory received his Ph.D. in Physics in 2014 from the University of Pittsburgh (USA) for experimental studies of two-dimensional turbulence. At OIST, Rory has continued working on two-dimensional turbulence in soap films and recently he has focused on experiments and simulations of transitional pipe flow.