Flow-roughness heterogeneity: critical obliquity and salient parameters

Zheng, Yan; Anderson, William

doi:10.1017/jfm.2020.1185

Cited by 6 publications

(4 citation statements)

References 60 publications

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“…The secondary vortex structure thus obtained is consistent with experimental observations of flows over damaged turbine blades [78,79]. In these studies, strips with low and high flow velocities were found out, which can be related with the presence of large-scale secondary flows [68,84]. As…”

Section: Secondary Flows Near Rough Surfacessupporting

confidence: 88%

Prandtl’s Secondary Flows of the Second Kind. Problems of Description, Prediction, and Simulation

2021

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Abstract— The occurrence of turbulent pulsations in straight pipes of noncircular cross-section leads to the situation, when the average velocity field includes not only the longitudinal component but also transverse components that form a secondary flow. This hydrodynamic phenomenon discovered at the twenties of the last century (J. Nikuradse, L. Prandtl) has been the object of active research to the present day. The intensity of the turbulent secondary flows is not high; usually, it is not greater than 2–3% of the characteristic flow velocity. Nevertheless, their contribution to the processes of transverse transfer of momentum and heat is comparable to that of turbulent pulsations. In this paper, a review of experimental, theoretical, and numerical studies of secondary flows in straight pipes and channels is given. Emphasis is placed on the issues of revealing the physical mechanisms of secondary flow formation and developing the models of the apriori assessment of their forms. The specific features of the secondary flow development in open channels and channels with inhomogeneously rough walls are touched upon. The approaches of semiempirical simulation of turbulent flows in the presence of secondary flows are discussed.

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Section: Secondary Flows Near Rough Surfacessupporting

confidence: 88%

Prandtl’s Secondary Flows of the Second Kind. Problems of Description, Prediction, and Simulation

2021

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“…2013; Barros & Christensen 2014; Anderson et al. 2015 a ; Pathikonda & Christensen 2017; Yang & Anderson 2017 a ; Awasthi & Anderson 2018; Zheng & Anderson 2021). Results will demonstrate that, indeed, - or -type roughness can regulate the polarity of roughness-driven secondary flows, where the former and latter induce upwelling and downwelling aloft streamwise-aligned roughness ‘rows’, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…In the present context, the relative excesses occur above the streamwise-aligned rows. For brevity, and because has been shown in complementary prior articles (Zheng & Anderson 2021), contours are not shown here. We have prepared targeted results of total streamwise–wall-normal turbulent stress, which is indicative of in rough wall channel turbulence.…”

Section: Resultsmentioning

confidence: 99%

Surface layer response to heterogeneous tree canopy distributions: roughness regime regulates secondary flow polarity

Joshi

Anderson²

2022

J. Fluid Mech.

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Large-eddy simulation was used to model turbulent atmospheric surface layer (ASL) flow over canopies composed of streamwise-aligned rows of synthetic trees of height, $h$ , and systematically arranged to quantify the response to variable streamwise spacing, $\delta _1$ , and spanwise spacing, $\delta _2$ , between adjacent trees. The response to spanwise and streamwise heterogeneity has, indeed, been the topic of a sustained research effort: the former resulting in formation of Reynolds-averaged counter-rotating secondary cells, the latter associated with the $k$ - and $d$ -type response. No study has addressed the confluence of both, and results herein show secondary flow polarity reversal across ‘critical’ values of $\delta _1$ and $\delta _2$ . For $\delta _2/\delta \lesssim 1$ and $\gtrsim 2$ , where $\delta$ is the flow depth, the counter-rotating secondary cells are aligned such that upwelling and downwelling, respectively, occurs above the elements. The streamwise spacing $\delta _1$ regulates this transition, with secondary cell reversal occurring first for the largest $k$ -type cases, as elevated turbulence production within the canopy necessitates entrainment of fluid from aloft. The results are interpreted through the lens of a benchmark prognostic closure for effective aerodynamic roughness, $z_{0,{Eff.}} = \alpha \sigma _h$ , where $\alpha$ is a proportionality constant and $\sigma _h$ is height root mean square. We report $\alpha \approx 10^{-1}$ , the value reported over many decades for a broad range of rough surfaces, for $k$ -type cases at small $\delta _2$ , whereas the transition to $d$ -type arrangements necessitates larger $\delta _2$ . Though preliminary, results highlight the non-trivial response to variation of streamwise and spanwise spacing.

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“…TBL flows over various spanwise-heterogeneous rough walls have received a great deal of attention in recent years (e.g. Nugroho et al 2013, Barros and Christensen 2014, Anderson et al 2015, Kevin et al 2017, Bai et al 2018, 2021, Medjnoun et al 2020, Xu et al 2020, Zheng and Anderson 2021. Compared with that over the smooth wall, TBL flows over the spanwise-heterogeneous rough walls are characterized by large variations of flow statistics along the spanwise direction.…”

Section: Introductionmentioning

confidence: 99%

Turbulent/non-turbulent interface of the turbulent boundary-layer over a spanwise-heterogeneous converging/diverging riblets rough wall

Huang,

Bai

2024

Fluid Dyn. Res.

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Turbulent boundary layer (TBL) flows over various spanwise-heterogeneous rough walls exhibit spanwise variations in turbulence statistics, implying modifications of the turbulent/non-turbulent interface (T/NTI). In this work, based on the datasets of TBL flows over a spanwise-alternating converging/diverging riblets wall, we investigate behavior of T/NTI, properties of ‘bubble’ and ‘drop’ that are associated with T/NTI, as well as connections between T/NTI and large-scale structures within the boundary layer. The flow datasets were obtained through stereoscopic particle image velocimetry (SPIV) measurements on the cross-stream plane of the TBL flow at a Reynolds number 〖Re〗_θ = 1.3  104. The T/NTI and associated ‘bubble’ and ‘drop’ are identified using a kinetic energy criterion, while the large-scale structures by a streak detection algorithm. It is observed that the T/NTI height and the occurrence of ‘bubble’ and ‘drop’ display a spanwise-heterogeneous feature, with lower T/NTI height and higher occurrence probability of ‘bubble’ over the diverging section of riblets than over the converging section of riblets. Results of conditional average show that the ‘bubble’ is associated with positive streamwise fluctuations, common-down flow and a pair of counter-rotating streamwise vortices, while the ‘drop’ with negative streamwise fluctuation, common-up flow and a pair of counter-rotating streamwise vortices. Probability density functions (PDF) of the ‘bubble’ size and fractal dimensions of the T/NTI are found similar for both the riblets and smooth wall flows. Furthermore, it is observed that the large-scale low-speed structures occurring preferentially over the converging section of riblets play a role in elevating T/NTI while the large-scale high-speed ones over the diverging section of riblets lowering down T/NTI.

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Flow-roughness heterogeneity: critical obliquity and salient parameters

Abstract: Abstract

Cited by 6 publications

References 60 publications

Prandtl’s Secondary Flows of the Second Kind. Problems of Description, Prediction, and Simulation

Prandtl’s Secondary Flows of the Second Kind. Problems of Description, Prediction, and Simulation

Surface layer response to heterogeneous tree canopy distributions: roughness regime regulates secondary flow polarity

Turbulent/non-turbulent interface of the turbulent boundary-layer over a spanwise-heterogeneous converging/diverging riblets rough wall

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