Low-and high-drag intermittencies in turbulent channel flows

Rishav Agrawal, Henry C.H. Ng, Ethan A. Davis, Jae Sung Park, Michael D. Graham, David J.C. Dennis, Robert J. Poole

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


Recent direct numerical simulations (DNS) and experiments in turbulent channel flow have found intermittent low-and high-drag events in Newtonian fluid flows, at Reτ = uτ h/ν between 70 and 100, where uτ, h and ν are the friction velocity, channel half-height and kinematic viscosity, respectively. These intervals of low-drag and high-drag have been termed “hibernating” and “hyperactive”, respectively, and in this paper, a further investigation of these intermittent events is conducted using experimental and numerical techniques. For experiments, simultaneous measurements of wall shear stress and velocity are carried out in a channel flow facility using hot-film anemometry (HFA) and laser Doppler velocimetry (LDV), respectively, for Reτ between 70 and 250. For numerical simulations, DNS of a channel flow is performed in an extended domain at Reτ = 70 and 85. These intermittent events are selected by carrying out conditional sampling of the wall shear stress data based on a combined threshold magnitude and time-duration criteria. The use of three different scalings (so-called outer, inner and mixed) for the time-duration criterion for the conditional events is explored. It is found that if the time-duration criterion is kept constant in inner units, the frequency of occurrence of these conditional events remain insensitive to Reynolds number. There exists an exponential distribution of frequency of occurrence of the conditional events with respect to their duration, implying a potentially memoryless process. An explanation for the presence of a spike (or dip) in the ensemble-averaged wall shear stress data before and after the low-drag (or high-drag) events is investigated. During the low-drag events, the conditionally-averaged streamwise velocities get closer to Virk’s maximum drag reduction (MDR) asymptote, near the wall, for all Reynolds numbers studied. Reynolds shear stress (RSS) characteristics during these conditional events are investigated for Reτ = 70 and 85. Except very close to the wall, the conditionally-averaged RSS is higher than the time-averaged value during the low-drag events.

Original languageEnglish (US)
Article number1126
Pages (from-to)1-28
Number of pages28
Issue number10
StatePublished - Oct 2020


  • Channel flow
  • Hibernating turbulence
  • Hot-film anemometry
  • Turbulence

ASJC Scopus subject areas

  • Information Systems
  • General Physics and Astronomy
  • Electrical and Electronic Engineering
  • Mathematical Physics
  • Physics and Astronomy (miscellaneous)


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