Effect of aspect ratio on developing and developed narrow open channel flow with rough bed

Abstract

This study attempts to unravel the effect of aspect ratio on the turbulence characteristics in developing and fully developed narrow open channel flows. In this regard, experiments were conducted in a rough bed open channel flow. Instantaneous 3D velocities were acquired using an acoustic Doppler velocimeter at various locations along the centerline of the flume. The variables of interest include the mean components of the flow velocity, turbulence intensity, wall normal Reynolds shear stress, correlation coefficient, turbulence kinetic energy, and anisotropy. A new correlation between the equivalent roughness and velocity shift from the smooth wall logarithmic equation as a function of aspect ratio is proposed. Aspect ratio was found to influence the velocity characteristics throughout the depth in the developing flow region, while the effects are confined to the outer layer for fully developed flows. New equations to describe the variation of turbulence intensities and turbulent kinetic energy are proposed for narrow open channel flows. Reynolds stress anisotropy analysis reveals that level of anisotropy in narrow open channel flow is less than in wide open channel flows. Finally, a linear regression model is proposed to predict flow development length in narrow open channel flows with a rough bed.

PIV Measurements of Open-Channel Turbulent Flow under Unconstrained Conditions

“…This is in stark contrast with the "often quoted lowest estimate of 320" [3]. More recently, Sarkar [8] and Mahananda et al [9,10] used ADV to measure the flow in an open-channel flow of a low aspect ratio (i.e., AR > 2). Of the studies briefly covered in this paragraph, these works stand out as they are the only ones that have investigated something more than the mean velocity data.…”

“…The detailed assessments of Sarkar [8] shows that the turbulent bursting within the dip of the outer flow showed that the non-dimensional Reynolds shear stress changes its sign from positive to negative within the dip. Mahananda et al [9,10], on the other hand, discovered that the AR and Reynolds number affect the velocity characteristics in the developing region. However, these works only provide single-point measurements and they do not consider the influence of Fr.…”

Turbulent Flow Structures in Developing and Fully-Developed Flows under the Impact of Downward Seepage

“…An effort was made to revise the literature equations proposed for wide-open-channel flows. Numerous models were recommended to predict the distributions of the turbulence intensities and the flow depths in wide channels [1,6,17,20,26,27]. The existing literature models have not considered the developing flow over the seepage bed, and the trends for the streamwise and vertical turbulence intensities in the developing and developed flows for the seepage experiments presented in Figures 5 and 6 do not match the universal models provided by previous studies.…”

“…The flow in open channels is mainly turbulent in nature. In general, open-channel flows are spatially varied in the field due to the frequent variations of the boundary conditions arising from the alterations in flow discharge, as well as other channel parameters [1]. The alterations in boundary conditions cause a flow disruption due to the variance of viscous, gravitational, and inertial forces.…”

“…The inner zone is again composed by the viscous sublayer and the fully turbulent inner region. It is important to investigate the fluid features in developing and developed open-channel flows to evaluate the fluid-sediment interface and sediment aggradation and degradation, which are closely related to the hydrodynamic features, such as the vertical profile of time-averaged velocities, turbulence intensities, Reynolds shear stresses, and turbulent kinetic energy [1]. The turbulent developing open-channel flow is a complex 3D flow governed by a seepage bed, the bed roughness, and other variables.…”