Contributions of different scales of turbulent motions to the mean wall-shear stress in open channel flows at low-to-moderate Reynolds numbers

Duan, Yanchong; Zhong, Qiang; Wang, Guiquan; Zhang, Peng; Li, Danxun

doi:10.1017/jfm.2021.236

Cited by 22 publications

(16 citation statements)

References 70 publications

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“…A similar approach was taken by Duan et al. (2021) to study the contribution of different-sized structures to mean wall shear stress in open-channel flows.…”

Section: Introductionmentioning

confidence: 99%

“…The most famous of these relationships and the one employed by Deck et al (2014) andDe Giovanetti et al (2016) is the so-called FIK relationship developed by Fukagata, Iwamoto & Kasagi (2002). A similar approach was taken by Duan et al (2021) to study the contribution of different-sized structures to mean wall shear stress in open-channel flows.…”

Section: Introductionmentioning

confidence: 99%

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On the enhancement of boundary layer skin friction by turbulence: an angular momentum approach

Elnahhas

Johnson

2022

J. Fluid Mech.

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Turbulence enhances the wall shear stress in boundary layers, significantly increasing the drag on streamlined bodies. Other flow features such as free stream pressure gradients and streamwise boundary layer growth also strongly influence the local skin friction. In this paper, an angular momentum integral (AMI) equation is introduced to quantify these effects by representing them as torques that alter the shape of the mean velocity profile. This approach uniquely isolates the skin friction of a Blasius boundary layer in a single term that depends only on the Reynolds number most relevant to the flow's engineering context, so that other torques are interpreted as augmentations relative to the laminar case having the same Reynolds number. The AMI equation for external flows shares this key property with the so-called FIK relation for internal flows (Fukagata et al., Phys. Fluids, vol. 14, 2002, pp. L73–L76). Without a geometrically imposed boundary layer thickness, the length scale in the Reynolds number for the AMI equation may be chosen freely. After a brief demonstration using Falkner–Skan boundary layers, the AMI equation is applied as a diagnostic tool on four transitional and turbulent boundary layer direct numerical simulation datasets. Regions of negative wall-normal velocity are shown to play a key role in limiting the peak skin friction during the late stages of transition, and the relative strengths of terms in the AMI equation become independent of the transition mechanism a very short distance into the fully turbulent regime. The AMI equation establishes an intuitive, extensible framework for interpreting the impact of turbulence and flow control strategies on boundary layer skin friction.

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“…A similar approach was taken by Duan et al. (2021) to study the contribution of different-sized structures to mean wall shear stress in open-channel flows.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the enhancement of boundary layer skin friction by turbulence: an angular momentum approach

Elnahhas

Johnson

2022

J. Fluid Mech.

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“…Another relevant identity was discovered by Renard & Deck (2016) (hereafter referred to as the RD decomposition), for which the skin-friction coefficient is expressed as the sum of integral terms belonging to the mechanical energy equation. Alternative identities for the skin-friction coefficients of these flows, derived from the vorticity equation, was obtained by Yoon et al (2016), and variants for open-channel flows were studied by Nikora et al (2019) and Duan et al (2021).…”

Section: Introductionmentioning

confidence: 99%

Integral relations for the skin-friction coefficient of canonical flows

Riccó

Skote

2022

J. Fluid Mech.

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We show that the Fukagata et al.'s (Phys. Fluids, vol. 14, no. 11, 2002, pp. 73–76) identity for free-stream boundary layers simplifies to the von Kármán momentum integral equation relating the skin-friction coefficient and the momentum thickness when the upper bound in the integrals used to obtain the identity is taken to be asymptotically large. If a finite upper bound is used, the terms of the identity depend spuriously on the bound itself. Differently from channel and pipe flows, the impact of the Reynolds stresses on the wall-shear stress cannot be quantified in the case of free-stream boundary layers because the Reynolds stresses disappear from the identity. The infinite number of alternative identities obtained by performing additional integrations on the streamwise momentum equation also all simplify to the von Kármán equation. Analogous identities are found for channel flows, where the relative influence of the physical terms on the wall-shear stress depends on the number of successive integrations, demonstrating that the laminar and turbulent contributions to the skin-friction coefficient are only distinguished in the original identity discovered by Fukagata et al. (Phys. Fluids, vol. 14, no. 11, 2002, pp. 73–76). In the limit of large number of integrations, these identities degenerate to the definition of skin-friction coefficient and a novel twofold-integration identity is found for channel and pipe flows. In addition, we decompose the skin-friction coefficient uniquely as the sum of the change of integral thicknesses with the streamwise direction, following the study of Renard & Deck (J. Fluid Mech., vol. 790, 2016, pp. 339–367). We utilize an energy thickness and an inertia thickness, which is composed of a thickness related to the mean-flow wall-normal convection and a thickness linked to the streamwise inhomogeneity of the mean streamwise velocity. The contributions of the different terms of the streamwise momentum equation to the friction drag are thus quantified by these integral thicknesses.

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“…Detailed reviews about methods to measure and estimate shear stress can be found in Huai et al [5]. Experimental setups range from large-scale measurements (e.g., Errico et al [6]) to highly controlled laboratory-based experiments (e.g., Duan et al [7] and Bashirzadeh et al [8]). The direct measurement of shear stress requires sensitivity to small changes in flow velocity, generates minimal flow disturbance, especially in the vicinity of the bed, and maintains the principle of no sliding of the material in the bed [9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Force Measurement with a Strain Gauge Subjected to Pure Bending in the Fluid–Wall Interaction of Open Water Channels

2022

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An experimental method to measure forces of small magnitude with a strain gauge as a force sensor in the fluid–wall interaction of open water channels is presented. Six uniaxial strain gauges were employed for this purpose, which were embedded across the entire sensing area and subjected to pure bending, employing two-point bending tests. Sixteen two-point bending tests were performed to determine the existence of a direct relationship between the load and the instrument signal. Furthermore, a regression analysis was used to estimate the parameters of the model. A data acquisition system was developed to register the behavior of the strain gauge relative to the lateral displacement induced by the loading nose of the universal testing machine. The results showed a significant linear relationship between the load and the instrumental signal, provided that the strain gauge was embedded between 30% and 45% of the central axis in the sensing area of the sensor (R2 > 0.99). Thus, the proposed sensor can be employed to measure forces of small magnitude. Additionally, the linear relationship between the load and the instrumental signal can be used as a calibration equation, provided that the strain gauge is embedded close to the central axis of the sensing area.

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Contributions of different scales of turbulent motions to the mean wall-shear stress in open channel flows at low-to-moderate Reynolds numbers

Abstract: Abstract

Cited by 22 publications

References 70 publications

On the enhancement of boundary layer skin friction by turbulence: an angular momentum approach

On the enhancement of boundary layer skin friction by turbulence: an angular momentum approach

Integral relations for the skin-friction coefficient of canonical flows

Force Measurement with a Strain Gauge Subjected to Pure Bending in the Fluid–Wall Interaction of Open Water Channels

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