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Interfacial instability of sand patterns induced by turbulent shear flow

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International Journal of Sediment Research 2021年第4期36卷 449-456页

作者： Sk Zeeshan Ali subhasish dey Department of Civil Engineering Indian Institute of Technology Hyderabad Department of Civil Engineering Indian Institute of Technology Kharagpur Department of Hydraulic Engineering State Key Laboratory of Hydro-Science and Engineering Tsinghua University

When a turbulent shear flow above a plane sand surface entrains sand grains, it generates a variety of sand patterns. Fluvial sand forms two major interfacial patterns: meso-scale dunes and antidunes, and large-scale bars. Measurements have evidenced that under erosive conditions, meso-scale patterns either change to or coexist with large-scale patterns. However, it remains elusive what exactly drives the switching of interfacial patterns and how the switching occurs. Here, we showdcombing a flow model with a grain transport model, allowing for both the surface and suspended sand fluxes dthat the switching of patterns emerges from the shear-driven complex feedback between grain transport and topographic perturbations. The switching predominantly depends on the magnitudes of the Rouse number and the grain size to undisturbed flow depth ratio. The model offers quantitative predictions of the maximum amplification of sand patterns and unveils a new attraction erepulsion phenomenon.

关键词： Instability Sand patterns Turbulent flow Sediment transport

Suspended load in flows on erodible bed

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International Journal of Sediment Research 2009年第3期24卷 315-324页

作者： Sujit K. BOSE subhasish dey Visiting Fellow Department of Civil Engineering Indian Institute of Technology Chair Prof. Department of Civil Engineering Indian Institute of Technology

Steady state suspended-load of sediment transported in flow over erodible beds usually is treated by the advection-diffusion approach, though in recent years, it is being treated as a two-phase flow phenomenon incorporating kinetics of sediment particles. Among the advection-diffusion approaches, Rouse’s equation is the well-known, although a number of researchers in later periods have attempted to improve it by modifying the mixing length concept taking into account other aspects. In this paper, the advection-diffusion approach and associated logarithmic law of flow velocity are revisited. It is concluded from the logarithmic law that the Reynolds shear stress is a linear function of height above the bed, which reduces to bed shear stress in the case of a long horizontal channel. As a consequence, it is shown that the volumetric concentration of sediment is best approximated by the sum of two power laws of height above the bed. An equation is derived for the suspended-load transport rate in terms of elementary functions.

关键词： Sediment transport Fluvial hydraulics Suspended load Open channel flow

Bedload transport from analytical and turbulence phenomenological perspectives

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International Journal of Sediment Research 2019年第6期34卷 509-530页

作者： subhasish dey Sk Zeeshan Ali Ellora Padhi Department of Civil Engineering Indian Institute of Technology Kharagpur Department of Hydraulic Engineering State Key Laboratory of Hydro-Science and EngineeringTsinghua University Physics and Applied Mathematics Unit Indian Statistical Institute Kolkata

In this paper,we present the dynamics of bedload transport from two different *** are the analytical perspective and the turbulence phenomenological *** bedload transport from the analytical perspective,we highlight the systematic advances in the analytical modelling of bedload transport over the *** advances are principally classified into three broad foundations,namely,the deterministic foundation,that includes the bed shear stress concept,stream power concept,force balance concept and bedform concept,and the probabilistic foundation and the turbulence phenomenological foundation of bedload *** bedload transport from the turbulence phenomenological perspective brings into focus the bedload-induced turbulence phenomenology,including the hydrodynamics of mobile-bed and water-worked bed *** also discuss the recent advances in the biofilm-coated bedload ***,conclusion is drawn,highlighting the major research challenges.

关键词： Bedload transport Fluvial hydraulics Sediment transport Turbulent flow

Response of Reynolds stresses and scaling behavior of high-order structure functions to a water-worked gravel-bed surface and its implication on sediment transport

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International Journal of Sediment Research 2022年第1期37卷 1-13页

作者： Nadia Penna Ellora Padhi subhasish dey Roberto Gaudio Dipartimento di Ingegneria Civile Università Della Calabria Department of Civil Engineering Shiv Nadar University Department of Civil Engineering Indian Institute of Technology Kharagpur

The aim of this experimental study is to investigate the interaction between turbulent flow and a gravelbed that mimics the actual roughness structures of a natural bed and its implication on sediment *** particular,the response of the Reynolds stresses and the role of intermittency to the bed roughness is the primary focus of the current *** this end,the flow field,measured with an Acoustice Doppler Velocimeter (ADV),is thoroughly examined,considering the conditional Reynolds shear stresses and the high-order structure functions of *** study results show that the features and the roughness structure of the water-worked gravel-bed (WWGB) have a strong impact on bursting *** reason for this is attributed to the flow layer above the crest in the WWGBs being primarily affected by sweep events rather than ejection events,although the latter events are prevalent in this flow layer in an immobile,man-made,*** coherent structures,which are primarily responsible for sediment transport,also are the key cause of the presence of an intermittency excess that breaks the Kolmogorov self-similarity hypothesis,leading to multi-fractal behavior of the velocity structure functions.

关键词： Water-worked bed Turbulent flow Sweeps Ejections High-order structure functions

NONUNIFORMOPEN CHANNEL FLOW WITH UPWARD SEEPAGE THROUGH LOOSE BEDS

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International Journal of Sediment Research 2003年第3期18卷 266-272页

作者： subhasish dey Dept. of Civil Engrg. Indian Inst. of Tech. Kharagpur 721302 West Bengal India. Fax: +91 3222 55303

The Reynolds stress and bed shear stress are important parameters in fluvial hydraulics. Steady-nonuniform flow in open channels with streamwise sloping beds having upward seepage through loose beds is theoretically analyzed to estimate the Reynolds stress and bed shear stress. Equations of the Reynolds stress and bed shear stress are developed, assuming a modified logarithmic velocity distribution law due to upward seepage, and using the Reynolds and continuity equations of two-dimensional flow in open channels.

关键词： Reynolds stress Bed shear Open channel flow Sedimentary beds Steady-nonuniform flow Seepage

INITIATION OF SHELL MOTION ON SAND BEDS: AN EXPERIMENTAL STUDY

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International Journal of Sediment Research 2002年第4期17卷 286-297页

作者： subhasish dey,Alok KUMAR Department of Civil Engineering Indian Institute of Technology Department of Civil Engineering Indian Institute of Technology Associate ProfessorKharagpur 721302 WestBengal India.Fax:+*** Student Kharagpur 721302 West Bengal India

Experimental study on initiation of bivalve shell motion on a horizontal sand bed, under a unidirectional flow of water, is presented. Experiments were carried out in a flume with three types of bivalve shells, namely Coquina Clam, Cross-barred Chione and Ponderous Ark, to test the condition for initiation of motion. The shape parameters of bivalve shells are defined appropriately. Experiments were conducted in a flume with a horizontal bed, and the critical shear stresses were estimated using Vanoni's side-wall correction. The characteristic parameters affecting the initiation of shell motion on a horizontal bed in rough-turbulent regime identified based on the physical reasoning and dimensional analysis are the Shields parameter (nondimensional critical shear stress), nondimensional competent mean velocity, nondimensional sand roughness, nondimensional flow depth and shape parameter. Equations of Shields parameter and nondimensional competent mean velocity for the initial movement of shells on a horizontal sand bed with convex upward and downward conditions are obtained using experimental data.

关键词： Bivalve shells Incipient motion Sediment transport Coastal sediment Hydrodynamics Threshold motion

REVIEW ON LOCAL SCOUR DUE TO JETS

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International Journal of Sediment Research 2004年第3期19卷 210-238页

作者： Arindam SARKAR,subhasish dey Doctoral Research Fellow Department of Civil Engineering Indian Institute of Technology Kharagpur 721302 West Bengal India. Associate Professor Department of Civil Engineering Indian Institute of Technology Kharagpur 721302 West Bengal India.

The safety of an apron of the energy dissipator is threatened by the large-scale scour in the downstream of the apron due to the erosive action of a horizontal jet issuing from a sluice opening. Also, large-scale deposition of the scoured sediments due to an impinging jet in a plunging pool type energy dissipator affects the passage of flow adversely in the downstream channels. Owing to the significant practical importance, the problem of local scour due to jets has been studied by many investigators. In this paper, a comprehensive review of the up-to-date investigations on local scour due to horizontal and impinging jets is presented including all possible aspects, such as scouring process, parameters affecting scour, time variation of scour, velocity distribution on the apron and within the scour hole, development of boundary layer thickness, bed shear stress, scour estimation formulas and protection works.

关键词： Scour Erosion Sediment transport Jets

VORTEX FLOW FIELD IN A SCOUR HOLE AROUND ABUTMENTS

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International Journal of Sediment Research 2003年第4期18卷 310-325页

作者： Abdul Karim BARBHUIYA,subhasish dey West Bengal India. Lecturer Department of Applied Mechanics National Institute of Technology Silchar 788010 Assam India Associate Professor Department of Civil Engineering Indian Institute of Technology Kharagpur 721302

The three-dimensional flow field in a scour hole around different abutments under a clear water regime was experimentally measured in a laboratory flume, using the Acoustic Doppler Velocimeter (ADV). Three types of abutments used in the experiments were vertical-wall (rectangular section), 45° wing-wall (45° polygonal section) and semicircular. The three-dimensional time-averaged velocity components were detected at different vertical planes for vertical-wall abutment and azimuthal planes for wing-wall and semicircular abutments. The velocity components were also measured at different horizontal planes. In the upstream, presentations of flow field through vector plots at vertical / azimuthal and horizontal planes show the existence of a primary vortex associated with the downflow inside the scour hole. On the other hand, in the downstream, the flow field shows a reversed flow near the abutments having a subsequent recovery with a passage of flow as a part of the main flow. The data presented in this p

关键词： Abutments Three-dimensional flow Vortex flow Open channel flow Scour Sediment transport Fluvial hydraulics

FLOW FIELD IN SCOURED ZONE OF CHANNEL CONTRACTIONS

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International Journal of Sediment Research 2004年第4期19卷 292-311页

作者： Rajkumar V. RAIKAR,subhasish dey Kharagpur 721302 West Bengal India. Doctoral Research Fellow Department of Civil Engineering Indian Institute of Technology Kharagpur 721302 West Bengal India. Associate Professor Department of Civil Engineering Indian Institute of Technology

Experiments were conducted in a laboratory flume to measure the two-dimensional turbulent flow field in the scoured zone of channel contractions under a clear-water scour condition. The Acoustic Doppler Velocimeter (ADV) was used to detect the flow field at different vertical lines along the centerline of uncontracted (main channel) and contracted zones of the channel. The distributions of time-averaged velocity components, turbulent intensity, turbulent kinetic energy, and Reynolds stresses are presented in nondimensional graphical form. The bed shear stresses are computed from the measured Reynolds stresses being in threshold condition within the zone of contraction where bed was scoured. The data presented in this paper would be useful to the investigators for the development of kinematic flow model and morphological model of scour at a channel or river contraction.

关键词： Channel contraction Open channel flow Turbulent flow Erosion Scour Sediment transport Fluvial hydraulics