Friction factor decomposition for rough-wall flows: theoretical background and application to open-channel flows

Nikora, Vladimir; Stoesser, Thorsten; Cameron, Stuart; Stewart, Mark T.; Papadopoulos, K.; Ouro, Pablo; McSherry, Richard; Zampiron, Andrea; Marušić, Ivan; Falconer, Roger Alexander

doi:10.1017/jfm.2019.344

Cited by 76 publications

(92 citation statements)

References 56 publications

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“…A similar conclusion follows from the study of Nikora et al. (2019), who investigated bed friction mechanisms in rough-bed OCFs. The mechanism regulating the friction at the bed appeared to be related to the interplay between turbulence and SCs.…”

Section: Introductionsupporting

confidence: 84%

“…Considering smooth triangular-shaped ridges on a hydraulically rough bed, it has been noted that (iii) the contribution of SCs to the overall friction factor depends on their size, attaining a maximum when they are comparable to the flow depth (Zampiron et al 2020a,b). A similar conclusion follows from the study of Nikora et al (2019), who investigated bed friction mechanisms in rough-bed OCFs. The mechanism regulating the friction at the bed appeared to be related to the interplay between turbulence and SCs.…”

Section: Introductionsupporting

confidence: 79%

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Momentum and energy transfer in open-channel flow over streamwise ridges

2021

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Section: Introductionsupporting

confidence: 84%

Section: Introductionsupporting

confidence: 79%

Momentum and energy transfer in open-channel flow over streamwise ridges

2021

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“…Care needs to be taken to avoid buoyancy effects, if the density of the material used for model production is lower than that of water [10]. Moreover, it is possible to scale the DEM with a desired scale factor before manufacturing the model, and CNC-manufacturing methods can also be used to produce scaled moulds [22,23].…”

Section: Introductionmentioning

confidence: 99%

“…The blocks used for the milling can consist of different materials such as foams and metal alloys, and the accuracy of the milled surface or object depends on the accuracy of the DEM as well as the size of the milling head [10]. The milling technique is used in various hydraulic laboratories for the construction of scale models and has already been successfully applied to construct artificial self-affine rough beds, scaled versions of rough waterways, conduits, and hydraulic structures [10,22,23,[32][33][34]. The accuracy of milled models is directly visible by eye, but has seldomly been quantified.…”

Section: Introductionmentioning

confidence: 99%

Technical Note: On the Production and Accuracy of CNC-Manufactured Hydraulic Scale Models

Aberle

Eikenberg

Branß

et al. 2021

Water

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This Technical Note addresses the workflow for the production of hydraulic scale models using a Computer Numerically Controlled (CNC) production technique and investigates the possibilities to accurately reproduce topographical roughness features. Focusing on the construction of three scale models of unlined rock blasted tunnels, their accuracy is evaluated based on the comparison of differences between scaled prototype point clouds obtained by terrestrial laser scanning, spatially filtered meshes that served as input for the milling of the models, and digital twins of the constructed models that were created by Structure from Motion photogrammetry. The direct comparison between the point clouds and meshes as well as the comparison of derived statistical parameters show that the models could be reproduced with a high degree of accuracy. Observed deviations between the point clouds of the milled models and the milling meshes, as well as the scaled original point cloud, are identified and discussed in light of the production technique and the accuracy of the applied methods for the comparison.

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“…The fluid flow was resolved using Hydro3D, a well-validated LES research code [28][29][30][31][32][33][34], including geometry-resolved simulations of vertical axis turbines [4,15] and the validation of an ALM for HATs [35]. The governing equations resolved in Hydro3D are the spatially filtered Navier-Stokes equations for turbulent, incompressible, three-dimensional flow:…”

Section: Large-eddy Simulationmentioning

confidence: 99%

An Actuator Surface Model to Simulate Vertical Axis Turbines

Massie

Ouro²,

Stoesser

et al. 2019

Energies

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An actuator surface model (ASM) to be employed to simulate the effect of a vertical axis turbine on the hydrodynamics in its vicinity, particularly its wake is introduced. The advantage of the newly developed ASM is that it can represent the complex flow inside the vertical axis turbine's perimeter reasonably well, and hence, is able to predict, with a satisfying degree of accuracy, the turbine's near-wake, with a low computational cost. The ASM appears to overcome the inadequacy of actuator line models to account for the flow blockage of the rotor blades when they are on the up-stream side of the revolution, because the ASM uses a surface instead of a line to represent the blade. The ASM was used on a series of test cases to prove its validity, demonstrating that first order flow statistics-in our study, profiles of the stream-wise velocity-in the turbine's vicinity, can be produced with reasonable accuracy. The prediction of second order statistics, here in the form of the turbulent kinetic energy (TKE), exhibited dependence on the chosen grid; the finer the grid, the better the match between measured and computed TKE profiles.Energies 2019, 12, 4741 2 of 16 thus, reducing noise and fish mortality [4]; and finally, the wake generated by a VATT recovers quickly, which is particularly beneficial in the context of turbine array design and optimisation [5].One of the earliest experimental studies on VATTs, from Brochier et al. in 1986 [6], provided a concise description of vortex shedding of VAT blades in a dynamic stall through flow visualisation and velocity profile measurements. Subsequent contributions then built upon these findings to render a comprehensive picture of the processes involved in the formation and recovery of the wake of a rotating VAT [5,[7][8][9][10][11][12][13]; to record quantitative data for use in numerical model validation [5,8,11,12]; and to investigate the performance of different turbines or turbine configurations [9,14]. The flow-dynamics have been shown to be strongly dependent on the tip-speed ratio (TSR) of the turbine, with the Reynolds number having little effect on the wake [7]. At a lower TSR, the turbine blades will undergo large angles of attack which results in greater flow separation on their inner sides leading to large vorticity shedding [11]; the blades will enter dynamic stall on the upstream side of their path, resulting in the shedding of two counter-rotating vortices, from the leading and trailing edges. These vortices are convected downstream by the mean flow, through the rotor's swept area and across the path of the blade, where the blade will interact with them, resulting in an increase in lift [6]. At a higher TSR, the larger relative velocity of the blades reduces the flow separation, and hence the role of the dynamic stall vortices on the turbine's hydrodynamics [4].The kinematics of a turbine governs the extraction of energy from the mean flow, resulting in a velocity deficit behind the rotor, with a greater velocity deficit observed when it is operating at hig...

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Friction factor decomposition for rough-wall flows: theoretical background and application to open-channel flows

Cited by 76 publications

References 56 publications

Momentum and energy transfer in open-channel flow over streamwise ridges

Momentum and energy transfer in open-channel flow over streamwise ridges

Technical Note: On the Production and Accuracy of CNC-Manufactured Hydraulic Scale Models

An Actuator Surface Model to Simulate Vertical Axis Turbines

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