Turbulent drag reduction by spanwise wall forcing. Part 1: Large-eddy simulations

Abstract

Turbulent drag reduction through streamwise travelling waves of spanwise wall oscillation is investigated over a wide range of Reynolds numbers. Here, in Part 1, wall-resolved large-eddy simulations in a channel flow are conducted to examine how the frequency and wavenumber of the travelling wave influence the drag reduction at friction Reynolds numbers $R{e}_{\tau }=951$ and $4000$. The actuation parameter space is restricted to the inner-scaled actuation (ISA) pathway, where drag reduction is achieved through direct attenuation of the near-wall scales. The level of turbulence attenuation, hence drag reduction, is found to change with the near-wall Stokes layer protrusion height ${\ell }_{0.01}$. A range of frequencies is identified where the Stokes layer attenuates turbulence, lifting up the cycle of turbulence generation and thickening the viscous sublayer; in this range, the drag reduction increases as ${\ell }_{0.01}$ increases up to $30$ viscous units. Outside this range, the strong Stokes shear strain enhances near-wall turbulence generation leading to a drop in drag reduction with increasing ${\ell }_{0.01}$. We further find that, within our parameter and Reynolds number space, the ISA pathway has a power cost that always exceeds any drag reduction savings. This motivates the study of the outer-scaled actuation (OSA) pathway in Part 2, where drag reduction is achieved through actuating the outer-scaled motions.

References in corpus (6)

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Cited by in corpus (6)

• Turbulent drag reduction by spanwise wall forcing. Part 2: High-Reynolds-number experiments
• On the relationship between manipulated inter-scale phase and energy-efficient turbulent drag reduction
• Turbulent skin-friction drag reduction via spanwise forcing at high Reynolds number
• Response of a turbulent boundary layer to steady, square-wave-type transverse wall-forcing
• Spanwise wall forcing can reduce turbulent heat transfer more than drag
• Direct numerical simulations of supersonic three-dimensional turbulent boundary layers