Flow and drag force around a free surface piercing cylinder for environmental applications

Ducrocq, Thomas; Cassan, Ludovic; Chorda, Jacques; Roux, Hélène

doi:10.1007/s10652-016-9505-9

Cited by 32 publications

(13 citation statements)

References 22 publications

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“…Moreover, the velocity fields at Re = 43 000 revealed two recirculation regions: (i) below the cylinder and (ii) behind the cylinder. The measurements in Chaplin and Teigen [16] also showed that C D values reach a maximum with respect to F r. The evolution of C D values is in agreement with the experiments of Ducrocq et al [17], who investigated the behavior of subcritical and supercritical flows for different slopes of a flume with 0.5 < F r < 2.3 and Re = 50 000.…”

Section: Introductionsupporting

confidence: 87%

Flow and air-entrainment around partially submerged vertical cylinders

2019

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In this study, a partially submerged vertical cylinder is moved at constant velocity through water, which is initially at rest. During the motion, the wake behind the cylinder induces freesurface deformation. Eleven cylinders, with diameters from D = 1.4 to 16 cm, were tested at two different conditions: (i) constant immersed height h and (ii) constant h/D. The range of translation velocities and diameters are in the regime of turbulent wake with experiments carried out for 4500 < Re < 240 000 and 0.2 < F r < 2.4, where Re and F r are the Reynolds and Froude numbers based on D. The focus here is on drag force measurements and relatively strong freesurface deformation up to air-entrainment. Specifically, two modes of air-entraiment have been uncovered: (i) in the cavity along the cylinder wall and (ii) in the wake of the cylinder. A scaling for the critical velocity for air-entrainment in the cavity has been observed in agreement with a simple model. Furthermore, for F r > 1.2, the drag force varies linearly with F r. c for h = 23 ± 0.1 cm and F r −4.7±0.51 c for h/D = 2.55 ± 0.05, in good agreement with the prediction of the model. The red shaded area refers to the range of dimensionless parameters where no air-entrainment in the cavity occurs. The black dashed-doted line represents the threshold Re/F r 25 000 above which air-entrainment occurs in the wake and in the cavity.Hence, air-entrainment requires large inertial effects or strong gravity effects. It is interesting to note that the stability diagram in Fig. 9(b) is consistent with the results of Kumagai et al.[42] for horizontal cylinder translating beneath an air-water interface.

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Section: Introductionsupporting

confidence: 87%

Flow and air-entrainment around partially submerged vertical cylinders

2019

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“…The picture are thresholded considering their pixels intensity and the particules detected are deleted if their length is superior to 50% of the mean diameter (1 cm). The used algorithm is detailed in Ducrocq et al [7], and the images were rectified with an homography matrix [28]. An example of the picture and the associated velocity vectors is given on Fig.…”

Section: Methodsmentioning

confidence: 99%

Velocity distribution in open channel flow with spatially distributed roughness

2019

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A numerical procedure is proposed to estimate the velocity distribution in open channel flow, for engineering applications. A method based on the mixing length model and subdivision of the wetted surface, is modified to easily integrate a lateral distribution of roughness. Several friction models for vegetated or rough flows can be added, two of which have been tested. The numerical procedure was developed with a commercial software (Matlab) to ensure fast computation and possible coupling with 1D hydraulic models. The validation of the computation has been done with rectangular and compound channels with spatially distributed roughness. The usefulness of the method for ecohydraulics is demonstrated with two applications: box culvert design for fish passes and 1D modelling of mountain river flows for which experimental results from a laboratory scale-model is compared to predictions. The interest of a friction law calibrated with a real grain roughness size is put forward.

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“…Studies on rock-ramps fishways [17,[26][27][28] have provided a better description of these functions experimentally and numerically. They depend on the characteristics of the macro-roughness elements and the conveyance velocity U:…”

Section: Emergent Roughness Elementsmentioning

confidence: 99%

A Semi-Analytical Model for the Hydraulic Resistance Due to Macro-Roughnesses of Varying Shapes and Densities

Cassan

Roux

Garambois

2017

Water

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A friction model resulting from investigations into macro-roughness elements in fishways has been compared with a broad range of studies in the literature under very different bed configurations. In the context of flood modelling or aquatic habitats, the aim of the study is to show that the formulation is applicable to both emergent or submerged obstacles with either low or high obstacle concentrations. In the emergent case, the model takes into account free surface variations at large Froude numbers. In the submerged case, a vegetation model based on the double-averaging concept is used with a specific turbulence closure model. Calculation of the flow in the roughness elements gives the total hydraulic resistance uniquely as a function of the obstacles' drag coefficient. The results show that the model is highly robust for all the rough beds tested. The averaged accuracy of the model is about 20% for the discharge calculation. In particular, we obtain the known values for the limiting cases of low confinement, as in the case of sandy beds.

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Flow and drag force around a free surface piercing cylinder for environmental applications

Cited by 32 publications

References 22 publications

Flow and air-entrainment around partially submerged vertical cylinders

Flow and air-entrainment around partially submerged vertical cylinders

Velocity distribution in open channel flow with spatially distributed roughness

A Semi-Analytical Model for the Hydraulic Resistance Due to Macro-Roughnesses of Varying Shapes and Densities

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