Drag Reduction of Turbulent Boundary Layers by Travelling and Non-Travelling Waves of Spanwise Wall Oscillations

Skote, Martin

doi:10.3390/fluids7020065

Cited by 4 publications

(9 citation statements)

References 23 publications

(57 reference statements)

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“…It will be shown in § 5 that the SSL in pipe flow can continuously drain energy from turbulence, leading to the gradual decay of turbulence and final relaminarization. When considering the temporal wall oscillation, the same trend can be observed for a channel ) and a turbulent boundary layer (Skote 2022), with the optimal oscillating period located at around T + = 100-125. It is already known that spatial oscillation can achieve more drag reduction than temporal oscillation (Viotti et al 2009;Skote 2013).…”

Section: Drag-reduction Resultssupporting

confidence: 63%

“…Hence it is necessary to compare the present results with the existing literature data, as shown in figure 3. Also included are the results from temporal wall oscillation in a pipe (Quadrio & Sibilla 2000;Choi et al 2002), a channel ) and a turbulent boundary layer (Skote 2022) since the wavelength (λ) and period (T) can be linked by (Quadrio et al 2009;Viotti et al 2009)…”

Section: Drag-reduction Resultsmentioning

confidence: 99%

“…Also included are the results from temporal wall oscillation in a pipe (Quadrio & Sibilla 2000; Choi et al. 2002), a channel (Quadrio & Ricco 2004) and a turbulent boundary layer (Skote 2022) since the wavelength () and period () can be linked by (Quadrio et al. 2009; Viotti et al.…”

Section: Control Resultsmentioning

confidence: 99%

“…It is shown that the effect of outer large-scale motions on drag reduction is subordinate. The latest numerical study of turbulent boundary layer with streamwise travelling-wave control was conducted by Skote (2022), with attention focused on the downstream development of drag reduction. The experiments conducted by Auteri et al (2010), which is the only experimental work in a pipe, and by Bird, Santer & Morrison (2018) in turbulent boundary layers both confirm the DNS results of Quadrio et al (2009).…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Turbulence suppression by streamwise-varying wall rotation in pipe flow

Liu

Zhu²,

Bao³

et al. 2022

J. Fluid Mech.

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Direct numerical simulations of turbulent pipe flow subjected to streamwise-varying wall rotation are performed. This control method is able to achieve drag reduction and even relaminarize the flow under certain control parameters at friction Reynolds number $Re_\tau =180$ . Two control parameters, which are velocity amplitude and wavelength, are considered. It is found that increasing the wavelength rather than increasing the amplitude seems to be a better choice to improve the control efficiency. An annular boundary layer, called the spatial Stokes layer (SSL), is formed by the wall rotation. Based on the thickness of the SSL, two types of drag-reduction scenarios can be identified roughly. When the thickness is low, the SSL acts as a spacer layer, inhibiting the formation of streamwise vortices and thereby reducing the shear stress. The flow structures outside the SSL are stretched in the streamwise direction due to the increased velocity gradient. Within the SSL, the turbulence intensity diminishes dramatically. When the thickness is large, a streamwise wavy pattern of near-wall streaks is formed. The streak orientation is dominated by the mean shear-strain vector outside the viscous sublayer, and there is a phase difference between the streak orientation and local mean velocity vector. The streamwise scales of near-wall flow structures are reduced significantly, resulting in the disruption of downstream development of flow structures and hence leading to the drag reduction. Furthermore, it is found that it requires both large enough thickness of the SSL and velocity amplitude to relaminarize the turbulence. The relaminarization mechanism is that the annular SSL can absorb energy continuously from wall-normal stress due to the rotational effect, thereby the turbulence self-sustaining process cannot be maintained. For the relaminarization cases, the laminar state is stable to even extremely large perturbations, which possibly makes the laminar state the only fixed point for the whole system.

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Section: Drag-reduction Resultssupporting

confidence: 63%

Section: Drag-reduction Resultsmentioning

confidence: 99%

Section: Control Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Turbulence suppression by streamwise-varying wall rotation in pipe flow

Liu

Zhu²,

Bao³

et al. 2022

J. Fluid Mech.

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Turbulent drag reduction by spanwise wall forcing. Part 2. High-Reynolds-number experiments

et al. 2023

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We present measurements of turbulent drag reduction (DR) in boundary layers at high friction Reynolds numbers in the range of $4500 \le Re_\tau \le 15\ 000$ . The efficacy of the approach, using streamwise travelling waves of spanwise wall oscillations, is studied for two actuation regimes: (i) inner-scaled actuation (ISA), as investigated in Part 1 of this study, which targets the relatively high-frequency structures of the near-wall cycle, and (ii) outer-scaled actuation (OSA), which was recently presented by Marusic et al. (Nat. Commun., vol. 12, 2021) for high- $Re_\tau$ flows, targeting the lower-frequency, outer-scale motions. Multiple experimental techniques were used, including a floating-element balance to directly measure the skin-friction drag force, hot-wire anemometry to acquire long-time fluctuating velocity and wall-shear stress, and stereoscopic particle image velocimetry to measure the turbulence statistics of all three velocity components across the boundary layer. Under the ISA pathway, DR of up to 25 % was achieved, but mostly with net power saving (NPS) losses due to the high-input power cost associated with the high-frequency actuation. The low-frequency OSA pathway, however, with its lower input power requirements, was found to consistently result in positive NPS of 5–10 % for moderate DRs of 5–15 %. The results suggest that OSA is an attractive pathway for energy-efficient DR in high-Reynolds-number applications.

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

Rouhi

Chandran

et al. 2023

J. Fluid Mech.

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Turbulent drag reduction (DR) through streamwise travelling waves of the 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 DR at friction Reynolds numbers $Re_\tau = 951$ and $4000$ . The actuation parameter space is restricted to the inner-scaled actuation (ISA) pathway, where DR is achieved through direct attenuation of the near-wall scales. The level of turbulence attenuation, hence DR, 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 DR 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 DR 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 DR savings. This motivates the study of the outer-scaled actuation pathway in Part 2, where DR is achieved through actuating the outer-scaled motions.

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Drag Reduction of Turbulent Boundary Layers by Travelling and Non-Travelling Waves of Spanwise Wall Oscillations

Cited by 4 publications

References 23 publications

Turbulence suppression by streamwise-varying wall rotation in pipe flow

Turbulence suppression by streamwise-varying wall rotation in pipe flow

Turbulent drag reduction by spanwise wall forcing. Part 2. High-Reynolds-number experiments

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

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