Search results for "Low velocity"

Dip Phenomenon in High-Curved Turbulent Flows and Application of Entropy Theory

2018

The estimation of velocity profile in turbulent open channels is a difficult task due to the significant effects of the secondary flow. The present paper investigates the mechanism of the velocity-dip phenomenon, whereby the location of the maximum velocity appears to be below the free surface. Previous studies conducted in straight channels relate the mechanism of the velocity-dip phenomenon to secondary flow induced by anisotropy of turbulence. This work focuses on high-curved channels where the secondary motion, which is also induced by the channel’s curvature, evolves along the bend. The width-to-depth ratio, B/h, is one of the most important parameters that are affecting the secondary …

Effects of Boulder Arrangement on Flow Resistance Due to Macro-Scale Bed Roughness

2023

Flow resistance in gravel-bed channels is not only affected by the shape and size of the roughness elements, but also by their arrangement on the channel bed surface (position to flow streamlines, spacing between elements, and their protrusion from the channel bed). Many investigations proved that open channel flow resistance can be obtained by integrating the power velocity profile. For a macro-scale roughness condition, this study aims to investigate the effect of different boulder arrangements on flow resistance. First, for each arrangement, the equation relating Γ function of the power velocity profile, the Froude number, and the channel slope was calibrated using available measur…

Application of the entropy model to high-curved turbulent flows

2018

The entropy-based approach allows the estimation of the mean flow velocity in open channel flow by using the maximum flow velocity. The entropy model allows to correlate the mean velocity, um, and the maximum velocity, umax by means of a linear relationship, um, = Φ (M) umax, which depends on the entropy parameter, M, characteristic of the fluvial section ([1]). The present work also focuses on high-curved channels where the secondary motion, which is also induced by the channel’s curvature, evolves along the bend. The study is motivated by the fact that meandering bends have radii of curvature continuously variable in stream-wise direction so that convective flow accelerations occur and th…

ENTROPY PARAMETER ESTIMATION IN A HIGH-CURVATURE CHANNEL: EXPERIMENTAL INVESTIGATION IN A LABORATORY FLUME

2017

The entropy model developed by Chiu (1988) allows to correlate the mean velocity, um, and the maximum velocity, umax by means of a linear relationship, um, = Φ (M) umax, which depends on the entropy parameter, M, characteristic of the fluvial section. This formulation was tested on several natural streams with different hydraulic and geometric characteristics (Ammari et al. 2010, Moramarco et al., 2004; Moramarco and Termini, 2015). In this paper, attention is focused on the verification of the entropic relationship between the mean velocity and maximum velocity in the presence of the forcing action due to the variable channel curvature and for different values of the aspect ratio. The anal…

Experimental investigation of flow characteristics in vegetated channels

2006

Assessing dye-tracer technique for rill flow velocity measurements

2018

Abstract Rill erosion is considered one of the most important processes affecting soil because of the large amount of soil loss. The rill network acts as sediment source and is able to transport both rill flow-detached particles and those delivered from the interrill areas. Small flow depth in a rill and steep slope values of its bed affect significantly flow hydraulics. When rill flow velocity is measured using a dye-tracing method, the mean velocity is calculated by multiplying the measured surface velocity of the leading edge of the tracer plume by a correction factor. The main uncertainty of the dye-tracing technique stands in the relationship between mean and surface flow velocity. In …

Comment on “Effects of different tillage practices on the hydraulic resistance of concentrated flow on the loess plateau in China” by J. Sun et al

2020

Abstract For concentrated flows, which are characterized by small water depth and steep sloping beds, hydraulic conditions different from those typical of streams and rivers occur. In this study a new theoretically deduced flow resistance equation was tested using the experimental data by Sun et al. for three different tilled surfaces (Manual Dibbling, MD, Manual Hoeing, MH, and Contour Drilling, CD). At first, the profile parameter-relationship, which is the relationship between the velocity profile parameter Γ, the channel slope and the flow Froude number, was calibrated using rill flow data by Di Stefano et al. Then, the applicability of this relationship was tested by the measurements o…

Experiments for testing soil texture effects on flow resistance in mobile bed rills

2018

Abstract In this paper a recently theoretically deduced rill flow resistance equation, based on a power-velocity profile, was tested experimentally on plots of varying slopes and soil texture in which mobile bed rills are incised. Measurements of flow velocity, water depth, cross section area, wetted perimeter and bed slope conducted in rill reaches incised on experimental plots, having different slope values (9, 14, 22, 24 and 26%) and soil texture (clay fraction ranging from 42 to 73%), and literature data were used to calibrate the flow resistance equation. In particular, the relationship between the velocity profile parameter Γ, the channel slope, the flow Froude number and texture frac…

Discharge estimation combining flow routing and occasional measurements of velocity

2011

A new procedure is proposed for estimating river discharge hydrographs during flood events, using only water level data at a single gauged site, as well as 1-D shallow water modelling and occasional maximum surface flow velocity measurements. One-dimensional diffusive hydraulic model is used for routing the recorded stage hydrograph in the channel reach considering zero-diffusion downstream boundary condition. Based on synthetic tests concerning a broad prismatic channel, the “suitable” reach length is chosen in order to minimize the effect of the approximated downstream boundary condition on the estimation of the upstream discharge hydrograph. The Manning’s roughness coefficient is calibra…

Experimental Analysis of Velocity Distribution in a Coarse-Grained Debris Flow: A Modified Bagnold’s Equation

2020

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