Turbulent skin-friction reduction by wavy surfaces

Abstract

Direct numerical simulations of fully-developed turbulent channel flows with wavy walls are undertaken. The wavy walls, skewed with respect to the mean flow direction, are introduced as a means of emulating a Spatial Stokes Layer (SSL) induced by in-plane wall motion. The transverse shear strain above the wavy wall is shown to be similar to that of a SSL, thereby affecting the turbulent flow, and leading to a reduction in the turbulent skin-friction drag. The pressure- and friction-drag levels are carefully quantified for various flow configurations, exhibiting a combined maximum overall-drag reduction of about 0.5%. The friction-drag reduction is shown to behave approximately quadratically for small wave slopes and then linearly for higher slopes, whilst the pressure-drag penalty increases quadratically. Unlike in the SSL case, there is a region of increased turbulence production over a portion of the wall, above the leeward side of the wave, thus giving rise to a local increase in dissipation. The transverse shear-strain layer is shown to be approximately Reynolds-number independent when the wave geometry is scaled in wall units.

References in corpus (8)

• Streamwise-traveling waves of spanwise wall velocity for turbulent drag reduction
• Reynolds-dependence of turbulent skin-friction drag reduction induced by spanwise forcing
• Experimental assessment of drag reduction by traveling waves in a turbulent pipe flow
• Streamwise oscillation of spanwise velocity at the wall of a channel for turbulent drag reduction
• The laminar generalized Stokes layer and turbulent drag reduction
• Performance losses of drag-reducing spanwise forcing at moderate values of the Reynolds number
• Prediction of turbulence control for arbitrary periodic spanwise wall movement
• Drag reduction by a solid wall emulating spanwise oscillations. Part 1

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• Response of a turbulent boundary layer to steady, square-wave-type transverse wall-forcing
• Turbulent separation control with a tilted wavy wall: a promising approach for energy savings in aerodynamic systems
• Sensitivity analysis of wavy wall performance in turbulent separation control: Effects of amplitude and period variations