Scour Caused by Wall Jets

Balachandar, Ram; Reddy, Haritha P.

doi:10.5772/54909

Cited by 10 publications

(9 citation statements)

References 52 publications

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“…Each curve can be divided into three stages: the short-term phase, where an intense extraction of sediment occurs in a short time span, followed by the development phase, where the scour process slows down, and, finally, the long-term phase, with Y 0 approaching an asymptotic mean value, Y ∞ . Earlier studies of bed scour caused by turbulent two-dimensional jets described such logarithmic dependence [17][18][19]. But, unlike those results, in the present configuration, the curves display a remarkable change at the critical value Q * = 7.5 l/min.…”

Section: The Long-term Scour Regimecontrasting

confidence: 87%

“…It has been claimed that the effect of grain size is not completely absorbed by F 0 [21,22], hence relative roughness, d s /b 0 , should be included in the analysis. Digging and refilling cycles have been also reported for AR ≫ 1, in experiments lasting hundreds of hours, being associated with jet-flipping (a phenomenon in which the jet suddenly flips from the bed to the water surface, and viceversa) [19,23].…”

Section: Introductionmentioning

confidence: 87%

“…For a layer of non-cohesive sediments immediately downstream of a rectangular opening, b 0 , the variation of the scour dimensions with the logarithm of time was found to be linear, and the scour process eventually attains an asymptotic stage, after several hours [18]. The maximum eroded depth, Y ∞ , made dimensionless with b 0 , was found to be mainly dependent on the densimetric Froude number, [19,20]. It has been claimed that the effect of grain size is not completely absorbed by F 0 [21,22], hence relative roughness, d s /b 0 , should be included in the analysis.…”

Section: Introductionmentioning

confidence: 92%

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Experimental study on the scour due to a water jet subjected to lateral confinement

Martino

Ciani

Paterson

et al. 2019

European Journal of Mechanics - B/Fluids

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The effect of lateral confinement due to very close side walls, on erosion caused by a water jet issuing from a rectangular sluice aperture, has been studied experimentally in a narrow laboratory flume. Velocimetry (PIV) in presence of a smooth, no erodible bottom, revealed self-similar velocity profiles with the structure of a wall jet, but upward-shifted with respect to the classical two-dimensional profile. The classical definition of the Shields number was modified, to include the influence of the relative roughness and the inlet aspect ratio. This last coefficient was also relevant in the definition of a suitable length scale to account for the effect of the lateral confinement. Scour patterns in the narrow flume have also shown differences with respect to erosion by two-dimensional wall jets: the downstream mound undergoes a morphological transition, from triangular to trapezoidal, at the early stage of the scour development, and grains move downhill driven by gravity inside the granular wedge, in a regime of steady recirculation (SR). Above this regime, a digging-refilling (DR) cycle, with periods of the order of seconds, triggers at a well-defined Shields number.

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Section: The Long-term Scour Regimecontrasting

confidence: 87%

Section: Introductionmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 92%

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Experimental study on the scour due to a water jet subjected to lateral confinement

Martino

Ciani

Paterson

et al. 2019

European Journal of Mechanics - B/Fluids

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“…Under water, scours caused by wall jets have been the focus of extensive work in the engineering context (e.g. Balachandar and Reddy 2013). Interestingly, Dumas et al (2005) noted that experimental bedforms created under combined flows had a "boxy profile" when stoss faces were steepened by intense local scouring.…”

Section: Erosional Structures From Turbulent Pyroclastic Currentsmentioning

confidence: 99%

Pyroclastic dune bedforms: macroscale structures and lateral variations. Examples from the 2006 pyroclastic currents at Tungurahua (Ecuador)

Douillet¹,

Bernard²,

Bouysson³

et al. 2018

Preprint

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Pyroclastic currents are catastrophic flows of gas and particles triggered by explosive volcanic eruptions. For much of their dynamics, they behave as particulate density currents and share similarities with turbidity currents. Pyroclastic currents occasionally deposit dune bedforms with peculiar lamination patterns, from what is thought to represent the dilute low concentration and fluid-turbulence supported end member of the pyroclastic currents. This article presents a high resolution dataset of sediment plates (lacquer peels) with several closely spaced lateral profiles representing sections through single pyroclastic bedforms from the August 2006 eruption of Tungurahua (Ecuador). Most of the sedimentary features contain backset bedding and preferential stoss-face deposition. From the ripple scale (a few centimetres) to the largest dune bedform scale (several metres in length), similar patterns of erosive-based backset beds are evidenced. Recurrent trains of sub- vertical truncations on the stoss side of structures reshape and steepen the bedforms. In contrast, sporadic coarse-grained lenses and lensoidal layers flatten bedforms by filling troughs. The coarsest (clasts up to 10 cm), least sorted and massive structures still exhibit lineation patterns that follow the general backset bedding trend. The stratal architecture exhibits strong lateral variations within tens of centimetres, with very local truncations both in flow-perpendicular and flow-parallel directions. This study infers that the sedimentary patterns of bedforms result from four formation mechanisms: (i) differential draping; (ii) slope-influenced saltation; (iii) truncative bursts; and (iv) granular-based events. Whereas most of the literature makes a straightforward link between backset bedding and Froude-supercritical flows, this interpretation is reconsidered here. Indeed, features that would be diagnostic of subcritical dunes, antidunes and ‘chute and pools’ can be found on the same horizon and in a single bedform, only laterally separated by short distances (tens of centimetres). These data stress the influence of the pulsating and highly turbulent nature of the currents and the possible role of coherent flow structures such as Görtler vortices. Backset bedding is interpreted here as a consequence of a very high sedimentation environment of weak and waning currents that interact with the pre-existing morphology. Quantification of near-bed flow velocities is made via comparison with wind tunnel experiments. It is estimated that shear velocities of ca 0.30 m.s-1 (equivalent to pure wind velocity of 6 to 8 m.s-1 at 10 cm above the bed) could emplace the constructive bedsets, whereas the truncative phases would result from bursts with impacting wind velocities of at least 30 to 40 m.s-1.

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“…Jetflipping results in alternate scouring and refilling of the scour hole during a flipping cycle. The jet-flipping phenomenon has been observed mostly downstream of two types of hydraulic structures: a sluice gate [Balachandar and Kells, 1997;1998;Balachandar and Reddy, 2013;Johnston, 1990;Johnston and Halliwell, 1986;Kurniawan and Altinakar, 2002;Xie and Lim, 2015]; and a submerged weir with a solid flat bed [Azimi et al, 2014;Fritz and Hager, 1998;Kabiri-Samani et al, 2010;Lin et al, 2008;Wu and Rajaratnam, 1996;Wu and Rajaratnam, 1998]. There is, however, very little…”

Section: Dey and Sarkarmentioning

confidence: 99%

Flow structures in evolving scour holes caused by 2-D plunging jets and wall jets

Si¹

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The author wishes to express his sincere gratitude to his supervisor, Prof. Lim Siow Yong, for his kindness and valuable guidance over the past years. Prof. Lim's profound knowledge and insightful advice lead the author to complete this dissertation. Prof. Lim mentored the author not only in the academic pursuit but also in the author's life.The author wishes to express his sincere gratitude to Prof. Wang Xikun, for his valuable instructions on the PIV system and the design of the experiment carried out at the Maritime Research Centre. Prof. Wang's help makes the pursuit of PhD study easier and more interesting.

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Scour Caused by Wall Jets

Cited by 10 publications

References 52 publications

Experimental study on the scour due to a water jet subjected to lateral confinement

Experimental study on the scour due to a water jet subjected to lateral confinement

Pyroclastic dune bedforms: macroscale structures and lateral variations. Examples from the 2006 pyroclastic currents at Tungurahua (Ecuador)

Flow structures in evolving scour holes caused by 2-D plunging jets and wall jets

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