Dejiang Long

Bio: Dejiang Long is an academic researcher from University of Alberta. The author has contributed to research in topics: Hydraulic jump & Turbulence. The author has an hindex of 3, co-authored 3 publications receiving 289 citations.

Structure of flow in hydraulic jumps

Abstract: A high-speed photographic study was made of the hydraulic jump. It was found that the surface roller was made up of several vortices. These vortices are generated in the early part of the jump and travel downstream. As they move downstream, they grow by pairing. At the same time, water spills down the steepened surface to replenish the toe and subsequently is rolled up into new vortices. A Fourier analysis of the time series of the toe position indicates a cyclic mechanism, the frequencies of which appear to scale with the upstream velocity and downstream depth.

LDA study of flow structure in submerged hydraulic jump

Abstract: This paper presents the results of a Laser Doppler Anemometry (LDA) study of submerged hydraulic jumps in a horizontal rectangular channel of constant width with the submergence factor S varying approximately from 0.20 to 1.70 and inlet Froude number Fx approximately equal to 3.0, 5.5 and 8JX Measurements include surface profiles, mean velocity components of u and v, turbulence shear stress and turbulence intensities Major flow characteristics of submerged hydraulic jumps are discussed and analyzed. The flow in the fully developed region is found to have some degree of similarity. It is also found that a submerged jump is three dimensional in nature.

A numerical study of submerged hydraulic jumps

Abstract: A standard two-dimensional k-e turbulence model is used to predict the mean flow and turbulence characteristics of submerged hydraulic jumps An offset control volume method is developed to facilitate computation of the variable free surface The numerical predictions are compared with experimental measurements under three conditions with supercritical Froude numbers ranging from 32 to 82 and submergence factors ranging from 024 to 085 Finally the numerical performance is evaluated and discussed in detail It is concluded that the model is adequate for predicting the surface profile, mean velocity field and to some extent, the turbulence structure of submerged hydraulic jumps

Morphodynamics and sedimentary structures of bedforms under supercritical-flow conditions: New insights from flume experiments

Abstract: Supercritical-flow phenomena are fairly common in modern sedimentary environments, yet their recognition and analysis remain difficult in the stratigraphic record. This fact is commonly ascribed to the poor preservation potential of deposits from high-energy supercritical flows. However, the number of flume data sets on supercritical-flow dynamics and sedimentary structures is very limited in comparison with available data for subcritical flows, which hampers the recognition and interpretation of such deposits. The results of systematic flume experiments spanning a broad range of supercritical-flow bedforms (antidunes, chutes-and-pools and cyclic steps) developed in mobile sand beds of variable grain sizes are presented. Flow character and related bedform patterns are constrained through time-series measurements of bed configurations, flow depths, flow velocities and Froude numbers. The results allow the refinement and extension of some widely used bedform stability diagrams in the supercritical-flow domain, clarifying in particular the morphodynamic relations between antidunes and cyclic steps. The onset of antidunes is controlled by flows exceeding a threshold Froude number. The transition from antidunes to cyclic steps in fine to medium-grained sand occurs at a threshold mobility parameter. Sedimentary structures associated with supercritical bedforms developed under variable aggradation rates are revealed by means of combining flume results and synthetic stratigraphy. The sedimentary structures are compared with examples from field and other flume studies. Aggradation rate is seen to exert an important control on the geometry of supercritical-flow structures and should be considered when identifying supercritical bedforms in the sedimentary record.

The flow field downstream of a hydraulic jump

Abstract: A control-volume analysis of a hydraulic jump is used to obtain the mean vorticity downstream of the jump as a function of the Froude number. To do this it is necessary to include the conservation of angular momentum. The mean vorticity increases from zero as the cube of Froude number minus one, and, in dimensionless form, approaches a constant at large Froude number. Digital particle imaging velocimetry was applied to travelling hydraulic jumps giving centre-plane velocity field images at a frequency of 15 Hz over a Froude number range of 2–6. The mean vorticity determined from these images confirms the control-volume prediction to within the accuracy of the experiment. The flow field measurements show that a strong shear layer is formed at the toe of the wave, and extends almost horizontally downstream, separating from the free surface at the toe. Various vorticity generation mechanisms are discussed.

Hydraulic Jumps on Corrugated Beds

Abstract: The results of a laboratory study of hydraulic jumps on corrugated beds are presented. Experiments were performed for a range of Froude numbers from 4 to 10. Three values of the relative roughness t/ y 1 of 0.50, 0.43, and 0.25 were studied. It was found that the tailwater depth required to form a jump was appreciably smaller than that for the corresponding jumps on smooth beds. Further, the length of the jumps was about half of those on smooth beds. The integrated bed shear stress on the corrugated bed was about 10 times that on smooth beds. The axial velocity profiles at different sections in the jump were found to be similar, with some differences from the profile of the simple plane wall jet. The maximum velocityum at any section in terms of the velocity U1 of the supercritical stream was correlated with the longitudinal distance x in terms of L, which is the distance where um50.5U1 , and this relation was the same as that for jumps on smooth beds with the difference that L/ y 1 was much smaller for jumps on corrugated beds. The normalized boundary layer thickness d/b, where b is the length scale of the velocity profile, was equal to 0.45 for jumps on corrugated beds compared to 0.16 for the simple wall jet. The results of this study show the attractiveness of corrugated beds for energy dissipation below hydraulic structures.

Hydraulic-Jump and Hyperconcentrated-Flow Deposits of a Glacigenic Subaqueous Fan: Oak Ridges Moraine, Southern Ontario, Canada

Abstract: The Oak Ridges Moraine in southern Ontario is a poly- genetic moraine constructed of a number of coalesced deposits of gla- cifluvial and glacilacustrine origin. A detailed study of the facies ar- chitecture has been completed on a series of pit sections extending ; 300 m subparallel to the paleoflow direction. Eight major lithofacies and five facies associations have been described. These data have been interpreted to be upper-flow-regime hyperconcentrated-flood-flow de- posits emplaced under a regime of rapid flow expansion and loss of transport capacity within a plane-wall jet with an associated hydraulic jump. Deposition from the plane-wall jet with jump occurred in three zones of flow transformation: zone of flow establishment, transition zone, and zone of established flow. Massive gravels with unconsolidated sand intraclasts and open-work gravel / gravel-sand couplets were de- posited in the zone of flow establishment by hyperconcentrated and supercritical flows, respectively. Immediately downflow low-angle cross-stratified sand incised by steep-walled scours infilled by diffusely graded sand define the transition zone, the zone of maximum vortex erosion, and the distal limit of deposits emplaced under upper-flow- regime conditions. These strata record rapid bed aggradation from sediment-laden supercritical flows that episodically were scoured by large vortices generated within migrating hydraulic jumps. Strati- graphically upward and downflow strata consist only of lower-flow- regime sedimentary structures. Medium-scale, planar cross-strata and small-scale cross-lamination related to migrating 2-D dunes and cur- rent ripples, respectively, characterize the zone of established flow. The facies and sediment architecture suggest that this fan was deposited during a relatively short period of time (days, weeks) by energetic sed- iment-laden floods.

Performance assessment of OpenFOAM and FLOW-3D in the numerical modeling of a low Reynolds number hydraulic jump

Abstract: A comparative performance analysis of the CFD platforms OpenFOAM and FLOW-3D is presented, focusing on a 3D swirling turbulent flow: a steady hydraulic jump at low Reynolds number. Turbulence is treated using RANS approach RNG k-e. A Volume Of Fluid (VOF) method is used to track the air-water interface, consequently aeration is modeled using an Eulerian-Eulerian approach. Structured meshes of cubic elements are used to discretize the channel geometry. The numerical model accuracy is assessed comparing representative hydraulic jump variables (sequent depth ratio, roller length, mean velocity profiles, velocity decay or free surface profile) to experimental data. The model results are also compared to previous studies to broaden the result validation. Both codes reproduced the phenomenon under study concurring with experimental data, although special care must be taken when swirling flows occur. Both models can be used to reproduce the hydraulic performance of energy dissipation structures at low Reynolds numbers. Two CFD models: OpenFOAM and FLOW-3D for hydraulic jump in low Reynolds numbers.Representative variables are compared for the two CFD results and experimental data.The model results are also compared to previous studies with good agreement.Both CFD codes had good behavior, but special care is required with swirling flows.A quantification of both models accuracy relating to studied variables is proposed.