Exact coherent states in plane Couette flow under spanwise wall oscillation

Bengana, Yacine; Yang, Qiang; Tu, Guohua; Hwang, Yongyun

doi:10.1017/jfm.2022.606

Cited by 3 publications

(3 citation statements)

References 126 publications

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“…We further checked that the structure tilting angle can roughly match the shear angle at y + ≈ 10 , similar to the situation in spanwise wall oscillation control (Touber and Leschziner 2012;Yakeno et al 2014). It is noted that the overall dynamic variation of the near-wall vortices and streaks has recently been computed with the exact coherent state in plane Couette flow under spanwise wall oscillation (Bengana et al 2022), and there is a qualitative agreement between the captured structure dynamics.…”

Section: Structure Dynamicssupporting

confidence: 55%

Turbulent Drag Reduction by Travelling Waves of Spanwise Lorentz Force

Yang

Chung

2023

Flow Turbulence Combust

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Travelling waves induced by spanwise Lorentz force for skin-friction drag reduction are studied in the present work using direct numerical simulations, with particular focus on the streamwise and spanwise travelling waves. The overall picture of drag reduction in the frequency-wavenumber parameter space, $$\omega -\kappa _x-\kappa _z$$ ω - κ x - κ z is uncovered. It is found that both drag reduction maps for the streamwise and spanwise travelling waves are featured with a drag reduction ($$\mathcal{D}\mathcal{R}$$ D R ) region and a drag increase ($$\mathcal{D}\mathcal{I}$$ D I ) region. For the streamwise travelling wave of spanwise Lorentz force, the $$\mathcal{D}\mathcal{R}$$ D R and $$\mathcal{D}\mathcal{I}$$ D I regions are located in the same parameter regime compared to that of the streamwise travelling wave of spanwise wall velocity, while for the spanwise travelling wave, the $$\mathcal{D}\mathcal{R}$$ D R variation at any fixed $$\kappa _z$$ κ z is similar to that of spanwise oscillating Lorentz force. An exploration of the oblique travelling wave with an angle to the mean flow shows that the optimal drag reduction appears when the wave travels backward relative to the flow direction, and the "ribbon" structure is a general phenomenon appearing in all oblique travelling wave cases. The ensemble averaged positive and negative quasi-streamwise vortices become asymmetric when the travelling wave is imposed, and the near-wall high- and low-speed streaks are significantly tilted in the spanwise direction. Spanwise oscillation, streamwise and spanwise travelling waves share strong similarity in the statistics, energy spectra as well as turbulent structure modulation.

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Section: Structure Dynamicssupporting

confidence: 55%

Turbulent Drag Reduction by Travelling Waves of Spanwise Lorentz Force

Yang

Chung

2023

Flow Turbulence Combust

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“…Recalling the thickness of LGSL is δ + = 20 for OC (figure 8b), a clear evidence shows that both the high-and low-speed streaks are significantly twisted inside and above the Stokes layer, up to y + ≈ 60. It is noted that such a dynamic variation of the near-wall vortices and streaks has recently been computed with the exact coherent state in the plane Couette flow with spanwise wall oscillation (Bengana et al, 2022), and there is a qualitative agreement between the captured dynamics. To verify the vortex structure behaviour for FST, SP and BST, the positive and negative λ 2 structures are conditioned in the positive and negative Lorentz force regions, separately.…”

Section: Structure Dynamicsmentioning

confidence: 71%

Turbulent Drag Reduction by Travelling Waves of Spanwise Lorentz Force

Yang

Chung

2022

Preprint

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Travelling waves induced by spanwise Lorentz force for skin-friction drag reduction are studied in the present work using direct numerical simulations, with particular focus on the streamwise and spanwise travelling waves. The overall picture of drag reduction in the ω+ − κx+ − κz+ parameter space is uncovered. It is found that both drag reduction maps for the streamwise and spanwise travelling waves are featured with a drag reduction (DR) region and a drag increase (DI) region. For the streamwise travelling wave of spanwise Lorentz force, the DR and DI regions are located in the same parameter regime compared to that of the streamwise travelling wave of spanwise wall velocity, while for the spanwise travelling wave, the DR variation at any fixed κz+ is similar to the spanwise oscillating Lorentz force. An exploration of the oblique travelling wave with an angle to the mean flow shows that the optimal drag reduction appears when the wave travels backward relative to the flow direction, and the “ribbon” structure is a general phenomenon appearing in all oblique travelling wave cases. The ensemble averaged positive and negative quasi-streamwise vortices become asymmetric when the travelling wave is imposed, and the near-wall high- and low-speed streaks are significantly twisted in the spanwise direction. Spanwise oscillation, streamwise and spanwise travelling waves share strong similarity in the statistics, energy spectra as well as turbulent structure modulation.

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“…Other possible extensions of this work are modulating the plates using spanwise velocities applied either on a single plate or on both. These types of modulation have been shown to substantially affect the properties of PCF [32], and could lead to unforseen interactions.…”

Section: Discussionmentioning

confidence: 99%

The effect of modulated driving on non-rotating and rotating turbulent plane Couette flow

Akhtar

Ostilla–Mónico

2022

J. Fluid Mech.

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Direct numerical simulations of turbulent non-rotating and rotating plane Couette flow with a periodically modulated plate velocity are conducted to study the effect of modulated forcing on turbulent shear flows. The time-averaged shear Reynolds number is fixed at $Re_S = 3 \times 10^4$ , which results in a frictional Reynolds number of approximately $Re_\tau \approx 400$ . The modulating frequency is varied in the range $Wo\in (20,200)$ , while the modulating amplitude is kept fixed at $10\,\%$ of the shear velocity except to demonstrate that varying this parameter has minimal effect. The resulting shear at the plates is found to be independent of the forcing frequency, and equal to the non-modulated baseline. For the non-rotating simulations, two clear flow regions can be seen: a near-wall region that follows Stokes’ theoretical solution, and a bulk region that behaves similar to Stokes’ solutions but with an increased effective viscosity. For high driving frequencies, the amplitude response follows the scaling laws for modulated turbulence of von der Heydt et al. (Phys. Rev. E, vol. 67, 2003, 046308). Cyclonic rotation is not found to modify the system's behaviour in a substantial way, but anti-cyclonic rotation changes significantly the system's response to periodic forcing. We find that the persistent axial inhomogeneities introduced by mild anti-cyclonic rotation make it impossible to measure the propagation of the modulation adequately, while stronger anti-cyclonic rotation creates regions where the modulation travels instantaneously.

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Exact coherent states in plane Couette flow under spanwise wall oscillation

Cited by 3 publications

References 126 publications

Turbulent Drag Reduction by Travelling Waves of Spanwise Lorentz Force

Turbulent Drag Reduction by Travelling Waves of Spanwise Lorentz Force

Turbulent Drag Reduction by Travelling Waves of Spanwise Lorentz Force

The effect of modulated driving on non-rotating and rotating turbulent plane Couette flow

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