Dey, Subhasish

This study presents a comprehensive dataset comprising multiple data packages derived from laboratory experiments on steady and unsteady hydraulic jumps interacting with a large-scale Gaussian-shaped bed obstacle in an open-channel flume. The primary objective was to accurately measure the impact of hydraulic jump on the free surface and the bed pressure along the obstacle, ensuring the transferability of the results. A multi-process method was followed: designed experiments were recorded, images were postprocessed, and water level data were digitalized. For steady conditions, the bed pressure along the obstacle were measured by piezometers. The repository data are organized and provided in a single package, supplemented by a second package containing panoramas for each experimental time instant and graphical representations of the data, facilitating rapid evaluation of the outcomes. This study provides versatile data that can be utilized in various ways, particularly for fluvial model validation and studying turbulence-driven phenomena in open-channel flows. The detailed methodology presented herein can contribute to the advancement of enhanced laboratory techniques to study similar flow problems. © The Author(s) 2024.

In this paper, we explore the formation of alternate river bars in the presence of submerged vegetation, modelled as uniformly spaced rigid cylinders. We analyse the stability of the erodible bed by coupling the Exner equation for bed evolution with the continuity and momentum equations for the fluid phase. Through linear and weakly nonlinear stability analyses, we predict the equilibrium wavelength and amplitude of vegetated alternate bars. The computational results hinge on two key parameters: the vegetation aspect ratio (vegetation height to diameter ratio) and the vegetation packing density (dimensionless frontal area per unit volume). We present streamwise flow velocity profiles for different vegetation aspect ratios and vegetation packing densities. We find that the equilibrium wavelength decreases with higher vegetation aspect ratio and vegetation packing density. Vegetation reduces the minimum channel aspect ratio required for the braided channel formation and the threshold channel aspect ratio for the alternate bar formation. The equilibrium amplitude increases with vegetation aspect ratio but reduces with vegetation packing density, eventually reaching a constant value. The predicted alternate bar wavelength and amplitude align with field observations in the Arc River, Hooge Raam River, Alpine Rhine River and Isère River. © 2025 The Author(s).

Turbulent stream approaching a cylinder embedded in an erodible bed triggers significant erosion to form a scour hole. We present a generalized scaling framework for the equilibrium scour depth at a circular cylinder by means of the similarity principle and discover that the similarity exponent can be uniquely determined through the turbulence phenomenology. We assess the veracity of our approach aided by the experimental and field data covering wide ranges of key parameters. The scaling law offers insight into how the dimensionless scour depth relates to the inertia, drag, shear, and threshold shear forces.

In this paper, the local flow and turbulence characteristics of rigid submerged vegetated flow are studied using the double-averaging methodology. Experimental results indicate that the double-averaged streamwise velocity profile above the canopy follows a logarithmic law, while the canopy-induced drag significantly reduces the velocity through the vegetation elements. At the canopy top, an inflection occurs in the velocity profile, implying the existence of the Kelvin-Helmholtz (K-H) instability. The faster-moving fluid above the canopy interacts with the slower-moving fluid within the canopy, creating a strong shear at the canopy top. This induces the Reynolds shear stress, which peaks at the canopy top. The localized accelerated and decelerated flow regions occurring within the canopy produce dispersive shear stress that enhances fluid mixing and momentum transport. The second-order correlation shows the presence of coherent structures at the canopy top due to the K-H instability. The third-order correlation and the quadrant analysis demonstrate that the sweep events dominate the flow in the canopy layer, and the ejection events prevail in the main-flow layer. The turbulent kinetic energy (TKE) fluxes also confirm these findings. The negative streamwise dispersive kinetic energy flux within the canopy suggests that local interactions transport the TKE upstream. The TKE production rate peaks near the canopy top, while the TKE dissipation rate continuously increases within the canopy down to the bed. Higher streamwise spatial fluctuations downstream of the vegetation elements result from the effect of the canopy on the flow. © 2025 Author(s).

This paper describes the results of a flume experimental campaign exploring the flow structure and turbulence characteristics in open-channel flows with submerged flexible vegetation, called Ceratophyllum demersum L. (also commonly known as rigid hornwort). The analysis allows us to formulate the distributions of time-averaged streamwise velocity, Reynolds shear stresses, and turbulent kinetic energy (TKE) in the fully developed flow under the influence of three different submerged vegetation densities. A method for calculating the Manning roughness coefficient in open channels with submerged flexible vegetation is proposed, and an empirical formula for the drag coefficient of submerged flexible vegetation is derived. The distribution of the eddy viscosity and the canopy top penetration depth are examined under the influence of submerged flexible vegetation. A TKE model is derived for open-channel flows with submerged flexible vegetation, considering the turbulence length scale ranging from 0.02 to 0.05 m. The model is then validated using the experimental data. The sensitivity of the turbulence model to the two key parameters—eddy penetration depth and turbulent length scale—is analyzed. This study provides an improved understanding and insights into the effects of the submerged flexible vegetation on the flow structure and turbulence characteristics. © 2025 Author(s).

Bioroughness plays an important role in modifying the velocity and sediment flux near the riverbed. It is therefore pertinent to study the influence of benthic fauna on the bed forms. To this end, large-eddy simulations are performed to investigate the influence of the arrays of mounds and their density on the turbulence characteristics in an open-channel flow. The simulated distributions of the time-averaged streamwise velocity and the turbulence intensity are in good agreement with the experimental data. Four numerical simulations are performed with varying streamwise spacings of mounds. Details of the time-averaged and instantaneous flow velocities are analyzed by multiple visualization methods, and the effects of the bioroughness density on the equivalent roughness height and the Darcy-Weisbach friction factor are quantified. The time-averaged flow in the wake of the mounds is characterized by a symmetric pair of vortices. The mounds behave like bluff bodies, increasing the riverbed roughness and heterogeneity in the flow environment. An increase in mound density is to promote the development of secondary currents and to increase the dispersive stress near the bed. The peaks of the Reynolds shear stress distributions decrease in both the streamwise and vertical directions for the high-density case due to a blockage effect. The instantaneous flow features, in the form of various turbulence structures, are generated near the top edge and the wake zone of mounds. The spacing between low-speed streaks decreases with an increase in equivalent roughness height. Multifrequency behavior that is observed is a result of shear layer roll-up from the edges of mounds and the flapping of wake. Finally, two formulas for equivalent roughness height and Darcy-Weisbach friction factor are proposed involving the bioroughness density and height. The findings demonstrate the effects of the bioroughness on the near-bed turbulence characteristics and sediment stability.

This study examines the instability of sand waves (dunes and antidunes) from both linear and weakly nonlinear perspectives. The linear and weakly nonlinear analyses use the standard linearization and the center manifold-projection technique, respectively. The mathematical framework includes the depth-averaged continuity and momentum equations, the advection–diffusion equation for suspended sediment concentration, and Exner’s equation for bed evolution. The streamline curvature is treated using the Boussinesq approximation. The model considers the departure of the pressure distribution from the hydrostatic law. Both modes of sediment transport, as bedload and as suspended load, are taken into consideration. The perturbations characterize the maximum growth rate for a selected wave number, called the resonant wave number, which is the most favorable wave number for the formation of sand waves. As the flow Froude number and the relative roughness number increase, the dimensionless resonant wave number decreases. The dimensionless amplitude of sand waves increases as the flow Froude number and the relative roughness number increase to achieve a maximum, and subsequently it decreases. The predicted wave number and amplitude of sand waves satisfactorily match the available experimental data.

The estimation of scour depth under pipelines, aligned transversely to river flow, has attracted much attention because of its importance in hydraulic engineering. Pipeline scour results from the interaction between the wake vortices induced downstream of the pipeline and the sediment bed beneath it. The core insight of this study is to seek a universal law that governs sediment-bed scour beneath pipelines in steady flow, particularly under the clear-water condition. The analysis begins with an approach that incorporates the similarity concept, with a specific focus on the incomplete similarity in the asymptotic function of the ratio of particle size to scour depth ratio as a power law. The power law exponent can be determined exclusively through Kolmogorov's energy cascade theory. Stemming from Kolmogorov's energy cascade theory (also called the phenomenological theory of turbulence), a universal law emerges, revealing that the equilibrium scour depth to pipe diameter ratio follows a two-thirds scaling law with a newly introduced “pipeline-scour number,” which encapsulates all key factors influencing pipeline scour. This number includes variables such as the approach mean flow velocity and depth, the threshold shear velocity for sediment motion, and the sediment particle size. It also captures essential hydrodynamic forces, including inertia, drag, shear, and threshold shear forces. Moreover, the scaling law incorporates an additional term that involves the drag coefficient with an exponent of 2/3, thereby accounting for the influence of the pipe shape on the equilibrium scour depth. The derived universal law is validated using the experimental data. © 2025 Author(s).

Quantifying turbulent friction holds significant importance, not only for understanding the fundamental flow physics but also for enriching system performance across a wide range of engineering applications. This vision article presents the state of the science of the turbulent friction in canonical flows, shedding light on its current status through a combination of theoretical developments and experimental observations. First, the article discusses the law of the wall, including the scaling behavior, the possible origin of the logarithmic law, and the effects of wall roughness. Then, it provides an overview of roughness height and its connection with the wall topography. The scaling behaviors of the logarithmic and power laws of turbulent friction are thoroughly appraised, offering insights into their implications. Additionally, the phenomenological models of turbulent friction based on the spectral and co-spectral budget theories are furnished. The behavior of turbulent friction for extremely large Reynolds number flows is examined, based on theoretical models and experimental data. The semiempirical finite Reynolds number model for turbulent friction is reviewed, emphasizing the pertinent scaling laws in various forms. The scaling laws of turbulent friction in curved-pipe and axisymmetric boundary layer flows are discussed. Finally, future research directions are outlined, highlighting the key challenges to be addressed.

A turbulent wall jet issuing tangentially over a loose sediment bed induces significant erosion, leading to the development of a scour hole. This perspective article presents a generalized scaling framework for determining the equilibrium scour depths caused by planar and circular wall jets. It applies the concept of similarity, including an incomplete similarity in the power-law asymptotic function of particle size to scour depth ratio. This framework demonstrates that the similarity exponent can be exclusively determined through the phenomenological theory of turbulence. The scaling laws reveal that the nondimensional scour depth obeys a linear-law with the respective planar and circular wall-jet scour numbers, which depend on issuing jet size, jet velocity, bed particle size, and threshold shear velocity. Moreover, the analysis reveals that for a given jet thickness equal to the jet diameter, the circular wall-jet scour number scales with the 3/5 power of the planar wall-jet scour number. The approach is extensively validated with the experimental data over a range of key parameters. The scaling laws provide valuable insights into the relationship between nondimensional scour depth and key hydrodynamic forces, including inertia, particle drag, shear, and threshold shear forces. © 2025 Author(s).