Downstream Regime Research Articles

Analysis of the hydraulic interference between the baffles and the composite hydraulic structure

The purpose of the present study is to examine the influence of baffles presence at downstream system on weir gate hydraulic response. Two baffles configuration (triangle and angle shapes) are installed in bed flume. Two different spacing are used between the baffles and two different directions for baffles are also adopted. The study tries to investigate the variation in upstream Froude number, downstream Froude number, Reynolds number, actual discharge, discharge coefficient, downstream average water depth and the hydraulic system efficiency which is expressed as function of downstream water depth. It has been shown that the number of baffles has a direct and significant impact on flow hydraulic characteristics of weir-gate structure regardless of the spacing between baffles and the direction of baffles related to flow. Baffles number and spacing have essential impact on the water flow velocity of system and this impact leads to increase the flow resistance. The results clarify that the upstream Froude number, downstream Froude number, Reynolds number, actual discharge and discharge coefficient are decreased with the increase in baffles number except the average downstream water depth which increases with increase in baffles number. The efficiency of hydraulic system gives a good indicator for using baffles with weir-gate structure. At the end this paper shows a fruitful result of efficiency. This experiment run condense on the baffle’s numbers and directions with respect to the water flow direction at the downstream regime. So, the rises in the water level relies on the numbers and directions of the baffles as compare to the case without using baffles at the flume downstream region. The actual discharge and weir-gate discharge coefficient are more sensitive to the increase in the baffles’ numbers and the baffles direction with respect to the water flow direction

Changes in the hydrological regime and channel morphology as the effects of dams and bridges in the Barakar River, India

The anthropogenic activities affect the river channel as well as the whole system in different magnitudes and dimensions. Barakar River, the main tributary to the Damodar River in eastern India, is modified by several engineering structures. Hydrological parameters, such as monthly discharge, peak flow discharge and geomorphological factors, such as gradient, width–depth ratio, grain size, braid–channel ratio, sinuosity ratio, riffle-pool sequence, and stream power are taken into consideration to highlight the significant alterations of the river due to dam and bridge construction. The alterations are assessed with the help of hydrological data, satellite images, and digital elevation data along with field survey. The downstream section of the dams, the river is characterised by high braiding, sinuous, total and unit stream power along with the presence of a box-shaped bedrock channel, high gradient, bed coarsening and armouring due to the release of high-velocity sediment-free ‘hungry water’. In the upstream reach, the grain size decreases towards the dam, and it increases suddenly with poor sorting at the immediate downstream regime of the dam. The effects of bridges on the Barakar river morphology include an increase of gradient, width and depth of the river channel at the downstream of the bridges. The construction of bridges influences riffle-pool sequences. Thereby, the pool depth spacing is greater than the riffle crest spacing. However, the integration of natural as well as human-induced factors can be the best approach to understand the anthropogenic alteration of the river. Moreover, construction of some check dams at the upper section of the tributaries of the Barakar River can be very effective for morphological stability.

Hydrodynamic loads on a water drain with cavitation quenchers

The data on the hydrodynamic loads on the water body in the presence of cavitating energy without erosive dampers on it are presented. It is shown that these loads increase in comparison with the non-cavitation mode, but, despite this, the use without cavitation dampers in appropriate conditions is advisable, providing favorable downstream regimes and reducing the volume of construction work and the cost of construction. It is proved that for multiple types without erosive energy absorbers, data were obtained on the averaged and pulsating vertical and horizontal loads on the absorbers and the slaughter plate, which allows us to carry out the required calculations of the strength and stability of the elements of the downstream devices. As a result of cavitation and cavitation studies of erosion-free energy absorbers in cavitation stands, coefficients of any resistance C x of several types of aerosol-free absorbers were obtained; as well as pulsation standards measured by “point” sensors for the vertical hydrodynamic effects of the flow on the water culvert in the installation zone of an erosion-free damper.

Flow Instabilities in Solar Jets in Their Upstream and Downstream Regimes

Abstract Using the Atmospheric Imaging Assembly 304 Å images obtained from the Solar Dynamics Observatory, we study two jets that occurred during the M5.8 class flare on 2017 April 3 and the M5.5 class flare on 2016 July 23, respectively. During the M5.8 class flare, many vortex-like structures occurred in the upstream and downstream regimes of the associated jet. While the jet was ejected upwards to the corona, some dark material at its base flowed through a bright structure with a velocity of 110 km s−1. The boundary between the material and the structure changed from smooth to uneven. Later, the jet material at the higher atmosphere started to fall down with velocities of over 200 km s−1, and the left boundary of the jet developed into a sawtooth pattern. The vortex-like structures were formed, and the growth rates of two structures were presented. During the M5.5 class flare, we also observed many vortex-like structures in the downstream regime of the jet. At the late stage of the jet, some material at the south boundary of the jet fell back to the solar surface, and vortex-like structures at the boundary grew from ripple-like minim into vortices with diameters of 3.4–5.4 Mm. The growth rates of the vortex-like structures were calculated. We suggest that the vortex-like structures in the upstream regime are the manifestations of Kelvin−Helmholtz instability, and those in the downstream regime are simultaneously driven by Kelvin−Helmholtz instability and Raleigh−Taylor instability.

Understanding the water balance paradox in the Athabasca River Basin, Canada

AbstractThis study demonstrates the importance of the including and appropriately parameterizing peatlands and forestlands for basin‐scale integrated surface–subsurface models in the northern boreal forest, with particular emphasis on the Athabasca River Basin (ARB). With a long‐term water balance approach to the ARB, we investigate reasons why downstream mean annual stream flow rates are consistently higher than upstream, despite the subhumid water deficit conditions in the downstream regimes. A high‐resolution 3D variably saturated subsurface and surface water flow and evapotranspiration model of the ARB is constructed based on the bedrock and surficial geology and the spatial distribution of peatlands and their corresponding eco‐regions. Historical climate data were used to drive the model for calibration against 40‐year long‐term average surface flow and groundwater observations during the historic instrumental period. The simulation results demonstrate that at the basin‐scale, peatlands and forestlands can have a strong influence on the surface–subsurface hydrologic systems. In particular, peatlands in the midstream and downstream regimes of the ARB increase the water availability to the surface–subsurface water systems by reducing water loss through evapotranspiration. Based on the comparison of forestland evapotranspiration between observation and simulation, the overall spatial average evapotranspiration in downstream forestlands is larger than that in peatlands and thus the water contribution to the stream flow in downstream areas is relatively minor. Therefore, appropriate representation of peatlands and forestlands within the basin‐scale hydrologic model is critical to reproduce the water balance of the ARB.

Avalanches dynamics in reaction fronts in disordered flows.

We report on numerical studies of avalanches of an autocatalytic reaction front in a porous medium. The front propagation is controlled by an adverse flow resulting in upstream, static, or downstream regimes. In an earlier study focusing on front shape, we identified three different universality classes associated with this system by following the front dynamics experimentally and numerically. Here, using numerical simulations in the vicinity of the second-order transition, we identify an avalanche dynamics characterized by power-law distributions of avalanche sizes, durations, and lateral extensions. The related exponents agree well with the quenched-Kardar-Parisi-Zhang theory, which describes the front dynamics. However, the geometry of the propagating front differs slightly from that of the theoretical one. We show that this discrepancy can be understood in terms of the nonquasistatic correction induced by the finite front velocity.

Conjugate natural convection flow over a vertical surface with radiation

Numerical study of conjugate natural convection flow over a finite vertical surface with radiation is reported in this article. Rosseland diffusion approximation is used to express the radiative heat flux term. The governing boundary-layer equations are made dimensionless by means of a suitable form of non-similarity transformation. These equations are obtained in three regimes: (1) upstream (when \(\xi \rightarrow 0\)), (2) downstream (when \(\xi \rightarrow \infty \)) and (3) entire regime and are solved numerically. The solutions in the upstream and downstream regimes are obtained via shooting method whereas two-point implicit finite difference method is used to get the solutions for the entire regime. It is seen that asymptotic solutions give accurate results when compared with the numerical solution of the entire regime. The results indicate that the flow field and the temperature distributions are greatly influenced by thermal radiation parameter , \(R_d\), surface temperature parameter, \(\theta _w\) and Prandtl number Pr. It is established from the analysis that recirculation occurs in the flow specifically for \(R_d=1.5\).

Radiation effects on natural convection flow over an inclined flat plate with temperature-dependent viscosity

The effect of radiation on laminar natural convection flow of a viscous incompressible fluid over a semi-infinite flat plate inclined at a small angle to the horizontal with strong temperature-dependent viscosity has been investigated. The Rosseland approximation is considered while modelling the problem. The non-similar equations are obtained for upstream, downstream, and entire regimes, which are then solved numerically. For constant viscosity, the series solution technique has been employed in order to obtain solutions that are valid near the leading edge as well as in the downstream regime. Later, solutions of the governing equations have been obtained using the finite difference method along with the Keller box technique, taking into consideration variable viscosity. Effects of physical parameters like conduction—radiation para-meter Rd, surface temperature parameter θw, variable viscosity parameter λ, and Prandtl number Pr are shown on the local skin-friction coefficient Cf and the local Nusselt number, Nu. Effects of the parameters on the streamlines are also shown around the point of separation that occurs along the negatively inclined surface.

Understanding sediment dynamics using geological and engineering approaches: A case study of the Buffalo River area of concern, Buffalo, New York

A combination of geological and engineering approaches was applied to better understand sediment movement along a contaminated river bed and provide support for remediation decision making. The geological approach, using sediment trend analysis (STA) and side‐scan sonar mapping, helps interpret sedimentary processes acting over longer terms, while the engineering approach, based on a three‐dimensional sediment transport model, illustrates sediment movement over shorter times, such as might be driven by storm events. The study site was the lower portions of the Buffalo River (Buffalo, NY), which is a tributary to Lake Erie and is an Area of Concern (AoC), as identified by the International Joint Commission due to beneficial use impairments primarily associated with contaminated sediment. Results from STA indicate two distinct flow regimes: a downstream regime dominated by fluvial processes and an upstream regime driven by changes in the level of Lake Erie. Where the two flow regimes intersect, sediment furrows are found. These features have been observed in this portion of the river over the past fifteen years and show characteristic ‘tuning forks’ opening in both upstream and downstream directions, indicating a bidirectional flow regime. Upstream movement of sediment also was found with the sediment transport model, which links hydrodynamic and particle tracking components to calculate transport pathways. Such movement is apparently generated by high amplitude seiches common to Lake Erie. Upstream sediment transport was not expected, but is consistent with the interpretation of results from each of the three different approaches. This combination of techniques has provided insights about short‐term and longer‐term sedimentation processes, which is helpful in choosing among management and remediation options for river restoration.

Low‐frequency wave characteristics in the upstream and downstream regime of the terrestrial bow shock

Collisionless shocks in space are accompanied by the low‐frequency waves of the magnetic field both upstream and downstream of the shock. However, characteristics of these waves in the plasma rest frame are poorly understood, since spatial scale such as wavelength is hardly determined using single or at best two spacecraft observations. Taking advantage of multipoint measurements of the Cluster spacecraft, we present a statistical study to reveal the rest frame properties of the waves in the terrestrial bow shock environment such as frequencies, wave numbers, phase velocities, propagation directions, polarization and transport ratios for the quasi‐parallel and the quasi‐perpendicular shock regimes and in the upstream region, the outer, the middle, and the inner magnetosheath. We find that the quasi‐parallel shock upstream waves (or the foreshock waves) exhibit properties of the fast mode wave excited by the ion beam instability. Upstream of the quasi‐perpendicular shock the waves also exhibit similar properties to the foreshock waves, but the wave mode identification needs further investigations. In the magnetosheath the waves exhibit properties which are persistent from the outer to the inner magnetosheath. They can be interpreted as the mirror mode coupled to the plasma inhomogeneity or as the slow mode. We also find an organization in the wave propagation pattern that the upstream waves propagate toward upstream, while the magnetosheath waves propagate toward the flank region and toward the magnetopause. It is concluded that wave properties are different between the upstream and the downstream regions, but they are similar between the quasi‐parallel and the quasi‐perpendicular shock regimes, suggesting that the upstream waves are not transmitted to the downstream region across the shock and that the downstream waves do not depend on the shock angle (between the upstream magnetic field and the shock normal direction).

Natural convection flow of a viscous fluid about a truncated cone with temperature dependent viscosity

The two-dimensional natural convection flow of a viscous incompressible fluid with temperature dependent viscosity about a truncated cone is considered. The governing equations for the flow are obtained by using suitable transformations and solved by using an implicit finite difference method. Perturbation solutions are obtained near the leading edge and in the downstream regime, and the results are obtained in terms of the local skin friction coefficient and the local Nusselt number. Perturbation solutions are compared with the finite difference solutions and are found to be in excellent agreement. The dimensionless velocity profiles and viscosity distribution are also presented graphically for various values of the viscosity variation parameter, ɛ, for small values of the Prandtl number appropriate for liquid metals.

Flow of a viscous incompressible fluid of temperature dependent viscosity past a permeable wedge with uniform surface heat flux

The effect of uniform suction on the steady two-dimensional laminar forced flow of a viscous incompressible fluid of temperature dependent viscosity past a wedge with uniform surface heat flux is considered. The governing equations for the flow are obtained by using suitable transformations and are solved by using an implicit finite difference method. Perturbation solutions are also obtained near the leading edge and in the downstream regime. The results are obtained in terms of the local skin friction coefficient and the rate of heat transfer for various values of the pertinent parameters, such as the Prandtl number, Pr, the velocity gradient parameter, m, the local suction parameter, ξ, and the viscosity variation parameter, ɛ. Perturbation solutions are compared with the finite difference solutions and are found to be in excellent agreement. The effect of ξ, m and ɛ on the dimensionless velocity profiles and viscosity distribution are also presented graphically for Pr = 0.7 and 7.0, which are the appropriate values for gases and water respectively.

Thermal radiation effects on the natural convection flow over an isothermal horizontal plate

The natural convection boundary layer flow with conduction-radiation interaction of a viscous incompressible fluid along an isothermal horizontal surface has been studied. The equations valid in the upstream, downstream as well as in the entire regime are obtained. Solutions of the non-similar equations governing the flow for the entire regime and the downstream regime are obtained by employing an efficient implicit finite difference approximation together with the Keller box method, for a Prandtl number of 0.73. Also, the effects of the pertinent parameters, R d, the radiation-conduction parameter and θw, the surface heating parameter are shown graphically in terms of the local skin-friction and the local rate of heat transfer. Comparison of the results obtained for the upstream and the downstream regimes shows good agreement over the entire regime. Effects of R d and θw are also shown on the streamlines and the isotherms.

A perturbation analysis and finite element approximate model for free surface flow over curved beds

AbstractA perturbation analysis is developed for 1‐D shallow water flow over a curved bed for applications such as spillways. The perturbation approach leads to a new formulation of the problem with associated weak integral statement and approximation using finite elements. The flow may exhibit a hydraulic jump in the downstream regime. An artificial dissipation technique is introduced to stabilize the non‐linear problem and suppress numerical oscillations. Numerical results demonstrate the performance of the model and compare it with the steep‐slope shallow water formulation corresponding to the model with zero curvature.