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Energy Cascade In Transitional Pipe Flows
Speaker Dr Rory T. Cerbus
Okinawa Institute of Science and Technology
Fluid Mechanics Unit, Okinawa, Japan
Date 19 May 2017 (Friday)
Time 15:00 - 16:00
Venue Room 4472 (Lifts 25-26), HKUST
In 1883 Osborne Reynolds discovered a peculiar state for flow of water in a pipe [1]. This state corresponds to the transition from the quiescent, laminar state at low Re (Reynolds number, a dimensionless measure of the flow velocity) to the roiling, turbulent state at high Re. The laminar state is devoid of fluctuations; the turbulent state is inundated by a broad range of fluctuations. The transitional state is distinct from the laminar and turbulent states, and consists of localized patches-- "flashes"--of fluctuations. Later work unveiled many features of these flashes: they can proliferate or fade away, maintain their shape or continually expand [2,3,4]. The nature of the fluctuations in the flashes, however, remained unknown. We conduct experiments of flow of water in a pipe and focus on the fluctuations in the flashes. Our results suggest a startling conclusion: the fluctuations in the flashes partake in the well-known Richardson-Kolmogorov energy cascade, the signature of high Re turbulent state. To wit, transition is not a distinct state: the flashes are turbulent [5].



  1. Reynolds, O. Proc. Roy. Soc. Lond. 35, 84–99 (1883).
  2. Wygnanski, I. & Champagne, F. J. Fluid Mech. 59, 281–335 (1973).
  3. Eckhardt, B., Schneider, T. M., Hof, B. & Westerweel, J. Annu. Rev. Fluid Mech. 39, 447– 468 (2007).
  4. Mullin, T. Ann. Rev. Fluid Mech. 43, 1–24 (2011).
  5. Rory T. Cerbus, Chien-chia Liu, Gustavo Gioia, Pinaki Chakraborty, arXiv:1701.04048