Turbulence in a skewed three‐dimensional wall‐bounded shear flow: effect of mean vorticity on structure modification

Holstad, Anders; Andersson, Helge I.; Pettersen, Bjørnar

doi:10.1002/fld.2639

Cited by 4 publications

(2 citation statements)

References 36 publications

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“…The result suggests that the positive or negative Lorentz force only favours one type of near-wall quasi-streamwise vortices, as in other three-dimensional turbulent boundary layers (e.g. Holstad et al, 2012). When visualised with the same λ 2 criteria, differences in the structure strength, tilting angle can be observed among OC, FST, SP and BST, as shown in figure 16.…”

Section: Structure Dynamicsmentioning

confidence: 90%

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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Section: Structure Dynamicsmentioning

confidence: 90%

Turbulent Drag Reduction by Travelling Waves of Spanwise Lorentz Force

Yang

Chung

2022

Preprint

View full text Add to dashboard Cite

show abstract

“…The result suggests that the positive or negative Lorentz force only favours one type of the near-wall quasi-streamwise vortices, as in other three-dimensional turbulent boundary layers (e.g. Holstad et al 2012).…”

Section: Structure Dynamicsmentioning

confidence: 91%

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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Modifications of the near-wall structures in thermally induced three-dimensional turbulent boundary layer

Elsamni

2013

Physics of Fluids

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Statistical analysis is carried out in order to examine the modifications of near wall coherent structures in a thermally induced three-dimensional turbulent boundary layer (3DTBL). The buoyancy forces modify the counter rotating vortices in the near-wall region with different degrees in a similar way to that produced by the pressure and shear driven three-dimensional turbulent boundary layer flows. Evidence of such modifications that is highlighted in the present study may explain the reduction of Reynolds shear stress and turbulence activities in the near-wall region. It has been shown that the induced three-dimensionality weakens the strength of near-wall vortices in such a way that vortices of one sign are weakened to produce ejections and those of the other sign are weakened to produce sweeps. In contrast to the hypotheses explaining the reduction of turbulence activities in pressure and shear driven 3DTBL flows, vortices rotating in the same direction as the background mean spanwise vorticity in the near-wall region are weakened much more than those rotating in the opposite direction.

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Turbulence in a skewed three‐dimensional wall‐bounded shear flow: effect of mean vorticity on structure modification

Cited by 4 publications

References 36 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

Modifications of the near-wall structures in thermally induced three-dimensional turbulent boundary layer

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