A large-scale control strategy for drag reduction in turbulent boundary layers

Wade Schoppa, Fazle Hussain

Research output: Contribution to journalArticlepeer-review

113 Scopus citations

Abstract

Using direct numerical simulations of turbulent channel flow, we present a new method for skin friction reduction, enabling large-scale flow forcing without requiring instantaneous flow information. As proof-of-principle, x-independent forcing, with a z wavelength of 400 wall units and an amplitude of only 6% of the centerline velocity, produces a significant sustained drag reduction: 20% for imposed counterrotating streamwise vortices and 50% for colliding, z-directed wall jets. The drag reduction results from weakened longitudinal vortices near the wall, due to forcing-induced suppression of an underlying streak instability mechanism. In particular, the forcing significantly weakens the wall-normal vorticity ωy flanking lifted low-speed streaks, thereby arresting the streaks' sinuous instability which directly generates new streamwise vortices in uncontrolled flows. These results suggest promising new drag reduction techniques, e.g., passive vortex generators or colliding spanwise jets from x-aligned slots, involving durable actuators and no wall sensors or control logic.

Original languageEnglish
Pages (from-to)1049-1051
Number of pages3
JournalPhysics of Fluids
Volume10
Issue number5
DOIs
StatePublished - May 1998

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