On a mechanism of near-wall reverse flow formation in a turbulent duct flow

Zaripov, Dinar; Ivashchenko, V. A.; Mullyadzhanov, R. I.; Li, Renfu; Михеев, Н. И.; Kähler, Christian J.

doi:10.1017/jfm.2021.526

Cited by 15 publications

(10 citation statements)

References 28 publications

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“…2019; Zaripov et al. 2021 a ). The backflow is also accompanied by a thin upstream near-wall high-speed layer which couples to a region of high skin friction whereas the large low-speed structure results in a streamwise-elongated region of negative skin friction (Vinuesa et al.…”

Section: Resultsmentioning

confidence: 99%

“…2020; Zaripov et al. 2021 a ) as shown in the instantaneous fields around a backflow region in figure 2 with its swirl centre indicated by ‘’ which resulted in a strong sweep region as marked in figure 2( a ). The distribution of LSMs associated with the backflow corresponds to the organised vortices described by Adrian, Meinhart & Tompkins (2000) where a large-scale low-speed structure is induced between the aligned legs of hairpin vortices which wrap around the low-speed structure with strong spanwise vortices as their heads along the inclined high-shear layer between the high- and low-speed structures (Guerrero et al.…”

Section: Introductionmentioning

confidence: 97%

“…The backflow was also investigated in the DNS of fully developed flows in ducts (Zaripov et al. 2021 a , b ) and toroidal pipes (Chin et al. 2018 a , 2020), and over wing sections (Vinuesa, Örlü & Schlatter 2017; Zaki et al.…”

Section: Introductionmentioning

confidence: 99%

“…2020; Zaripov et al. 2021 a ). The backflow and the accompanied extreme wall-normal velocity fluctuations near the wall are coupled with negative skin friction associated with APG as shown in figure 2( b ).…”

Section: Introductionmentioning

confidence: 99%

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Backflow structures in turbulent pipe flows at low to moderate Reynolds numbers

2023

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The statistical characteristics and the evolution of the backflow structures are investigated in wall-bounded flows at Reynolds numbers up to $Re_{\tau }=1000$ . The backflow is caused by the joining of large-scale high- and low-speed structures in the vicinity of the wall and is formed at the tail tip of the low-speed structure. The distribution density of the backflow structures and the percentage area of the backflow region on the wall both increase with the Reynolds number. The backflow structures have an average lifespan of 8 wall units which is found to be slightly longer in the pipe than the channel, and they are convected downstream at the average velocities of the buffer region of approximately 10 wall units, similar to Cardesa et al. (J. Fluid Mech., vol. 880, 2019, R3). The backflow structures occasionally split and merge, and can form detached from the wall. Evidence shows that the split, merged and wall-detached backflow structures are caused by the near-wall structures. The split backflow structures are on average, larger and more spanwise-elongated which are split due to the spanwise shearing of the near-wall streaks. A backflow structure is formed detached from the wall when the trailing end of its carrier low-speed structure ‘sits’ on the near-wall high-speed streaks. The wall-detached backflow structures tend to become wall-attached by approaching the wall when undergoing a similar life cycle to the normal backflow of growth and decay with spanwise elongation because the backflow region at the tail of the low-speed structure is continuously pressed down to the wall by the high-speed structure driven by persistent vortical structures in the buffer region.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Backflow structures in turbulent pipe flows at low to moderate Reynolds numbers

2023

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“…In Ref. [23], mechanisms leading to transient near-wall reverse flow events in a square duct are proposed.…”

Section: Introductionmentioning

confidence: 99%

Resolvent Analysis of laminar and turbulent duct flows

Lopez-Doriga¹,

Dawson²,

Vinuesa³

2022

Preprint

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This work applies resolvent analysis to incompressible flow through a rectangular duct, in order to identify dominant linear energy-amplification mechanisms present in such flows. In particular, we formulate the resolvent operator from linearizing the Navier-Stokes equations about a two-dimensional base/mean flow. The laminar base flow only has a nonzero streamwise velocity component, while the turbulent case exhibits a secondary mean flow (Prandtl's secondary flow of the second kind). A singular value decomposition of the resolvent operator allows for the identification of structures corresponding to maximal energy amplification, for specified streamwise wavenumbers and temporal frequencies. Resolvent analysis has been fruitful for analysis of wall-bounded flows with spanwise homogeneity, and here we aim to explore how such methods and findings can extend for a flow in spatial domains of finite spanwise extent. We investigate how linear energy-amplification mechanisms (in particular the response to harmonic forcing) change in magnitude and structure as the aspect ratio (defined as the duct width divided by its height) varies between one (a square duct) and ten. We additionally study the effect that secondary flow has on linear energy-amplification mechanisms, finding that in different regimes it can either enhance or suppress amplification. We further investigate how the secondary flow alters the forcing and response mode shapes leading to maximal linear energy amplification.

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