Can large-scale oblique undulations on a solid wall reduce the turbulent drag?

Chernyshenko, S. I.; Leschziner, M. A.

doi:10.1063/1.5003617

Cited by 41 publications

(27 citation statements)

References 39 publications

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“…However, these schemes often deliver small benefits, or are unsuited to air. Recently, Ghebali et al [ 5 ] explored a novel passive technique using an inclined wavy surface to bring about a drag reduction of 0.5 % in a direct numerical simulation (DNS) of channel flow. The wavy walls drive spanwise momentum to emulate a spatial Stokes’ layer, and favourably alter the flow.…”

Section: Introductionmentioning

confidence: 99%

Experimental Control of Turbulent Boundary Layers with In-plane Travelling Waves

Bird

Santer

Morrison

2018

Flow Turbulence Combust

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The experimental control of turbulent boundary layers using streamwise travelling waves of spanwise wall velocity, produced using a novel active surface, is outlined in this paper. The innovative surface comprises a pneumatically actuated compliant structure based on the kagome lattice geometry, supporting a pre-tensioned membrane skin. Careful design of the structure enables waves of variable length and speed to be produced in the flat surface in a robust and repeatable way, at frequencies and amplitudes known to have a favourable influence on the boundary layer. Two surfaces were developed, a preliminary module extending 152 mm in the streamwise direction, and a longer one with a fetch of 2.9 m so that the boundary layer can adjust to the new surface condition imposed by the forcing. With a shorter, 1.5 m portion of the surface actuated, generating an upstream-travelling wave, a drag reduction of 21.5% was recorded in the boundary layer with Reτ = 1125. At the same flow conditions, a downstream-travelling produced a much smaller drag reduction of 2.6%, agreeing with the observed trends in current simulations. The drag reduction was determined with constant temperature hot-wire measurements of the mean velocity gradient in the viscous sublayer, while simultaneous laser Doppler vibrometer measurements of the surface recorded the wall motion. Despite the mechanics of the dynamic surface resulting in some out-of-plane motion (which is small in comparison to the in-plane streamwise movement), the positive drag reduction results are encouraging for future investigations at higher Reynolds numbers.

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Section: Introductionmentioning

confidence: 99%

Experimental Control of Turbulent Boundary Layers with In-plane Travelling Waves

Bird

Santer

Morrison

2018

Flow Turbulence Combust

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“…13,14 To date, in most experimental implementations, the wall is physically displaced, where the operating range of such approaches is largely limited by mechanical inertia 8,15 and resonant effects. 9,16,17 As a notable exception, Ghebali et al 18 used a particular undulated surface to passively reproduce the shear profile introduced by StTW for a distinct flow speed.…”

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confidence: 99%

Stokes-layer formation under absence of moving parts—A novel oscillatory plasma actuator design for turbulent drag reduction

2019

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A novel plasma actuator concept is proposed to mimic the effect of spanwise wall oscillations without mechanically moving parts, where four groups of electrodes and three independently operated high-voltage power supplies maintain a pulsatile dielectric barrier discharge (DBD) array. Time-resolved planar velocity fields are obtained with high-speed particle image velocimetry (PIV) in proximity of the discharge zones for quiescent ambient conditions. Resulting flow topologies and wall-normal velocity profiles indicate the Stokes-layer-like flow formation, which is elevated above the wall due to the no-slip condition. The underlying body forces are derived from the PIV data to provide further insight into cause-effect relations between pulsatile discharge and oscillatory flow. The momentum transfer domain is found to be only interrupted with the width of the exposed electrode, which is an important step toward homogeneous virtual wall oscillations. A comparison with earlier studies by Gatti et al. ["Experimental assessment of spanwise-oscillating dielectric electroactive surfaces for turbulent drag reduction in an air channel flow," Exp. Fluids 56, 110 (2015)] leads to the hypothesis that DBD-based turbulent drag reduction might be a competing alternative to conventional active and passive shear-layer formation strategies, where the adjustability of both oscillation frequency and velocity amplitude might cover a wide range of Reynolds numbers.

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“…The other group of passive techniques is called passive-neutral methods, such as riblets (García-Mayoral & Jiménez 2011) or dimples (van Nesselrooij et al 2016) that instead do not transfer power from the wall turbulence to the exterior of the fluid control volume because they are rigid and stationary. Passive-neutral devices nonetheless involve a power penalty within the fluid control volume with respect to the reference case, caused by a larger wetted area for riblets and dimples, or detrimental pressure drag for dimples, wavy walls (Ghebali, Chernyshenko & Leschziner 2017) and baffles (Marensi et al 2020).…”

Section: Power Consumed By the Moving Discsmentioning

confidence: 99%