Reynolds stresses transport in a turbulent channel flow subjected to streamwise traveling waves

Tardu, Sedat F.; Umair, Mohammad; Doche, Olivier

doi:10.1103/physrevfluids.7.054601

Cited by 5 publications

(19 citation statements)

References 45 publications

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“…Note that the profile of P 4 ω x ω x in HWO case collapse almost perfectly with the STW case A0.30. This strengthens again the observation made by Umair et al (2022) that the direct effects of STW mainly appear at A > 0.30.…”

Section: Streamwise Enstrophy Transportsupporting

confidence: 91%

“…Furthermore, we show the influence of STW on the near-wall quasistreamwise vortical structures, and estimate the DR margin using their drift. Finally, we explain the appearance of organized regular patterns of spanwise fluctuating velocity field observed by Umair et al (2022).…”

mentioning

confidence: 80%

“…Statistical data for these cases were obtained by averaging 25 full 3-D snapshots of instantaneous velocities and pressure fields, covering a time window of approximately 5000 wall units separated by approximately 200 wall units. Further details about the numerical schemes and the description of the code MULTIFAST used to perform the calculations are provided in Bauer, Tardu & Doche (2015) and Umair et al (2022).…”

Section: Numerical Detailsmentioning

confidence: 99%

“…For the A1.25 case, there is only a slight variation of ω x ω x between the local minimum and the wall, whereas in the case of uncontrolled flow there is an approximately 400 % increase at the same range of wall-normal distance. This is related to the lack of velocity-pressure gradient correlation in the spanwise velocity transport equation in the near-wall region (Umair et al 2022).…”

Section: Streamwise Enstrophy Transportmentioning

confidence: 99%

“…Most of the advances towards understanding the underlying physical mechanism mentioned above stem from the HWO forcing. In the context of STW, not much has been reported, except for the recent study by Umair, Tardu & Doche (2022) who adopted a similar approach to Touber & Leschziner (2012) and studied the full Reynolds stresses budgets in the flows controlled using STW. In this paper, delving deeper in to the mechanism, we investigate the vorticity transport in a turbulent channel flow with STW actuation.…”

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confidence: 99%

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Vorticity transport in a turbulent channel flow subjected to streamwise travelling waves

Umair

Tardu

2023

J. Fluid Mech.

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Direct numerical simulations of turbulent channel flow subjected to spanwise wall oscillations in the form of streamwise travelling waves (STW) were performed in an effort to elucidate the mechanism responsible for the observed drag reduction. We imposed large amplitudes to identify the proper effects of STW, while keeping the angular frequency and wavenumber fixed at a particular values. We primarily focus on the vorticity transport mechanism, to better understand the influence of STW actuation on the near-wall turbulence. We identify key terms appearing in the turbulent enstrophy transport equations that are directly linked to the STW actuation. The analysis reveals that the primary effect of the STW forcing is to attenuate the spanwise turbulent enstrophy at the wall, which is linked to the fluctuating wall shear stress. The suppression of the wall-normal turbulent enstrophy is deemed to be subordinate. To strengthen this point, we performed numerical experiments, where the streamwise fluctuating velocity, and consequently the spanwise vorticity, is artificially suppressed next to the wall. The anisotropic invariant maps show striking resemblance for large amplitude STW actuation and artificially forced cases. Detailed analysis of various structural features is provided, which includes the response of the near-wall streaks and shear layers of spanwise fluctuating velocity field. The quasistreamwise vortices, which play a key role in the regeneration mechanism, are shown to be pushed away from the wall, resulting in their weakened signature at the wall.

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Section: Streamwise Enstrophy Transportsupporting

confidence: 91%

mentioning

confidence: 80%

Section: Numerical Detailsmentioning

confidence: 99%

Section: Streamwise Enstrophy Transportmentioning

confidence: 99%

mentioning

confidence: 99%

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Vorticity transport in a turbulent channel flow subjected to streamwise travelling waves

Umair

Tardu

2023

J. Fluid Mech.

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Effect of Streamwise Travelling Waves on Coherent Vortices and Fine Structure of Wall Turbulence

Umair,

Tardu

2024

Springer Proceedings in Physics

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Skin-friction drag reduction by local porous uniform blowing in spatially developing compressible turbulent boundary layers

Gao

et al. 2022

Physics of Fluids

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This paper investigates the effects of local porous uniform blowing on the skin-friction drag reduction in the spatially developing compressible turbulent boundary layers through direct numerical simulations. Under the influence of uniform blowing, the skin-friction drag decreases drastically within the controlled regions, and the effect extends downstream. The drag reduction rate exceeds 10% for the uniform blowing velocities considered herein. The intrinsic mechanism of decreased skin-friction drag is further explored, in terms of the various contributions to this quantity, the Reynolds shear stress budget, and the multi-scale distributions and transfer of enhanced turbulent motions. The numerical results for the identity of Renard and Deck ["A theoretical decomposition of mean skin friction generation into physical phenomena across the boundary layer," J. Fluid Mech. 790, 339-367 (2016)] indicate that the decreased skin-friction drag is reflected in a negative contribution in the streamwise developing direction. The enhanced turbulent motion is investigated through the Reynolds shear stress budget, and uniform blowing is found to strengthen the magnitudes of all budget terms. We conclude that uniform blowing promotes the energy cascade process in the near-wall region, promoting the appearance of smaller turbulent structures and the formation of large outer scales. Similar skin-friction drag reduction in the subsonic case is also observed in a supersonic case. The upstream transition process is delayed, which leads to a relatively larger skin-friction drag reduction rate in a supersonic case. Finally, we investigate the porosity effects on the skin-friction drag, and conclude that the blowing flux is a decisive factor.

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Reynolds stresses transport in a turbulent channel flow subjected to streamwise traveling waves

Cited by 5 publications

References 45 publications

Vorticity transport in a turbulent channel flow subjected to streamwise travelling waves

Vorticity transport in a turbulent channel flow subjected to streamwise travelling waves

Effect of Streamwise Travelling Waves on Coherent Vortices and Fine Structure of Wall Turbulence

Skin-friction drag reduction by local porous uniform blowing in spatially developing compressible turbulent boundary layers

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