Channel Velocity Research Articles

Flow and turbulence in unevenly obstructed channels with rigid and flexible vegetation

The pattern of vegetation along the cross-section of macrophyte-dominated shallow waters is generally uneven, which affects water velocity and turbulence. This study examined the velocity and turbulence in the open channel with an uneven transverse distribution of vegetation in laboratory flume experiments. Two vegetation patterns were tested: emergent vegetation which covered part of the channel, and a symmetrical combination of submerged and emergent vegetation canopies along the lateral direction of the flume. The flow was measured using a three-dimensional Acoustic Doppler Velocimeter. The velocity and turbulence characteristics were analyzed under three vegetation densities and five discharge scenarios. Results showed that the longitudinal mean velocity changed with vegetation density and flow discharge when vegetation was unevenly distributed in a lateral direction. The strong variation in shear stress at the emergent vegetation–open water intersections and submerged–emergent vegetation intersections resulted in large-scale vortices at the interfaces. The formation processes of stem-scale turbulence and shear-scale turbulence under different vegetation scenarios were discussed. A turbulent kinetic energy model within partly obstructed vegetation canopies was established, which helped to identify the development of horizontal and vertical coherent vertices.

An Analytical Solution to Predict the Distribution of Streamwise Flow Velocity in an Ecological River with Submerged Vegetation

Aquatic submerged vegetation is widespread in rivers. The transverse distribution of flow velocity in rivers is altered because of the vegetation. Based on the vegetation coverage, the cross-section of the ecological channels can be divided into the non-vegetated area and the vegetated area. In the vegetated area, we defined two depth-averaged velocities, which included the water depth-averaged velocity, and the vegetation height-averaged velocity. In this study, we optimized the ratio of these two depth-averaged velocities, and used this velocity ratio in the Navier–Stokes equation to predict the lateral distribution of longitudinal velocity in the open channel that was partially covered by submerged vegetation. Based on the Navier–Stokes equations, the term “vegetation resistance” was introduced in the vegetated area. The equations for the transverse eddy viscosity coefficient ξ, friction coefficient f, drag force coefficient Cd, and porosity α were used for both the non-vegetated area and the vegetated area, and the range of the depth-averaged secondary flow coefficient was investigated. An analytical solution for predicting the transverse distribution of the water depth-averaged streamwise velocity was obtained in channels that were partially covered by submerged vegetation, which was experimentally verified in previous studies. Additionally, the improved ratio proposed here was compared to previous ratios from other studies. Our findings showed that the ratio in this study could perform velocity prediction more effectively in the partially covered vegetated channel, with a maximum average relative error of 4.77%. The improved ratio model reduced the number of parameters, which introduced the diameter of the vegetation, the amount of vegetation per unit area, and the flow depth. This theoretical ratio lays the foundation for analyzing the flow structure of submerged vegetation.

Horizontal Trash Rack Diverter Trash (HTDT) to Minimize Trash Clogging at the Intake of Micro-Hydro Power Plant

Clogging of Trash at the Micro Hydro-Power Plant can reduce the discharge, head, and micro-hydro production. Trash racks are currently less efficient in solving Trash clogging, so it needs appropriate technology innovation with the Horizontal Trash rack Diverter Trash (HTDT) which functions to get rid of or divert Trash. Diversion of Trash as well as increasing and stabilizing the discharge is important so that the innovation of adding a flow steering valve is needed (HTDT+V). The results of the research at β20° is the most optimal angle, the highest speed at the intake channel Cm4 V 0.7 m/s and HTDT + V β20° V 0.8 m/s occurs an increase in speed. Trash paste time β20° t 2.76 seconds, faster than the angle β0°, β5°, β30° Trash paste time t3.5 seconds. The HTDT+V installation increases the inflow velocity (V) in the intake channel by 60% and increases the discharge (Q) by 50%.

A 0.6 Mpc H i structure associated with Stephan’s Quintet

Stephan’s Quintet (SQ, co-moving radial distance = 85 ± 6 Mpc, taken from the NASA/IPAC Extragalactic Database (NED)1) is unique among compact groups of galaxies2–12. Observations have previously shown that interactions between multiple members, including a high-speed intruder galaxy currently colliding into the intragroup medium, have probably generated tidal debris in the form of multiple gaseous and stellar filaments6,8,13, the formation of tidal dwarfs7,14,15 and intragroup-medium starbursts16, as well as widespread intergalactic shocked gas5,10,11,17. The details and timing of the interactions and collisions remain poorly understood because of their multiple nature18,19. Here we report atomic hydrogen (H i) observations in the vicinity of SQ with a smoothed sensitivity of 1σ = 4.2 × 1016 cm−2 per channel (velocity bin-width Δv = 20 km s−1; angular resolution = 4′), which are about two orders of magnitude deeper than previous observations8,13,20,21. The data show a large H i structure (with linear scale of around 0.6 Mpc) encompassing an extended source of size approximately 0.4 Mpc associated with the debris field and a curved diffuse feature of length around 0.5 Mpc attached to the south edge of the extended source. The diffuse feature was probably produced by tidal interactions in early stages of the formation of SQ (>1 Gyr ago), although it is not clear how the low-density H i gas (NH i ≲ 1018 cm−2) can survive the ionization by the intergalactic ultraviolet background on such a long time scale. Our observations require a rethinking of properties of gas in outer parts of galaxy groups and demand complex modelling of different phases of the intragroup medium in simulations of group formation.

Shear induced lift and rotation on MicroFiber deposition in low Reynolds number flows

Lateral migration is of significant importance to fiber deposition in wall-bounded flows, especially when other active external physical transport mechanisms are absent. Due to great technical difficulty, investigation on this phenomenon is limited to fundamental derivations, and the implication to particle deposition has not been fully explored. To fill the gap, this study investigated the shear-induced lift and rotation on microfiber transport and deposition in low Reynolds number flows. Transport and deposition of non-neutrally buoyant ellipsoidal fibers in Poiseuille flow in horizontal and vertical channels is systematically examined, and various lateral migration scenarios are carefully investigated. It was found out that, in absence of the sideway gravity, shear-induced lift and rotation cause the fibers to drift across main streamlines in the vertical channel. This lateral movement is either the driving force for fiber deposition in a downward flow or pushes the particles toward channel center in an upward flow configuration. Lateral migration velocity in the vertical channel is found to correlate positively with fiber length and shear rate. Lateral migration is negligible in a horizontal channel where the sideway gravity is dominant. Current study clearly identified the presence of fiber transport scenarios where lateral migration driven by the shear-induced lift and rotation is the major contributor for fiber deposition in wall-bounded flows. The finding is of particular significance to practical applications, as frequently, they involve a combination of these transport scenarios either actively or passively. The study also provided additional insights to examine the equivalency of spheres to fiber dynamics.

Investigation on novel inertial minichannel to mitigate maldistribution induced high temperature zones

Axial conduction in channels depends on inlet velocity and thermal conductivity of the working fluid. In the case of parallel channels, axial conduction depends on heat sink configuration and inlet velocity. That at increased flow rates, the parallel channel generates flow maldistribution and develops localized high temperature zones in the heat sink. Effective use of heat sink configuration to mitigate axial conduction is found in the literature; however, the axial conduction effects are not suppressed in the parallel channels. Henceforth, the present study provides experimental and numerical insight to evaluate the potential of ribs and inertial based spillway channels to overcome the above mentioned problems in parallel channels. Especially, four different heat sink concepts were designed using copper material; normal channel, ribbed channel, ribbed inclined, and ribbed lifted. In which normal channel is experimented with and used as a reference, while the remaining channel types were investigated numerically. The factors such as maldistribution, thermal resistance, and pressure drop are considered to evaluate the impact of the ribs on inlet velocity. The ribbed inclined channel was found to perform better than other types and developed a 33 % lower center channel velocity than the normal channel. The temperature near the exit of the ribbed inclined channel was observed to be more even and the entire width of the minichannel was maintained at 47 °C, this trend was not noticed using other configurations.

Hydrodynamics of a tidal inlet under gray to green coastal protection interventions

Structural coastal protection interventions have been implemented worldwide to stabilize channels and shorelines in tidal inlets. Although these conventional “gray” interventions typically attain their goals, there is an increasing interest and need to consider nature-based or “green” interventions that also address system resilience and environmental impacts. For a better implementation of gray to green interventions in tidal inlets, their effectiveness and their effects on the velocity of these dynamic coastal systems need to be understood. The effects on flow velocity of gray to green coastal protection interventions for tidal inlets are assessed here by exploring six interventions intended to protect against erosion on the estuarine-side shoreline near the inlet. A field-calibrated numerical model with Willmott Skill scores rated as excellent for Oregon Inlet located in North Carolina, United States, is used to simulate tidal currents under present conditions and after implementing a seawall, a set of bendway weirs, a terminal groin extension, a dual-jetty system, a flood channel relocation, and an island restoration project. Comparisons of time series of flow velocities in the flood channel along an eroding, estuarine shoreline are used to identify the effectiveness of each coastal protection alternative at reducing erosive velocities. Geospatial difference maps are used to determine velocity changes caused by each alternative throughout the inlet system. With no coastal protection interventions, the velocities along the eroding shoreline exceeded an erosive threshold velocity (defined as 0.2 m/s) during 50% of the simulated period. Alternatives closer to the green side of the coastal protection intervention spectrum, such as channel relocation and island restoration, tend to display the most effectiveness at reducing flow velocities at the eroding shoreline while resulting in minimal inlet-wide hydrodynamic changes. On the other hand, gray alternatives either cause minimal (seawall and bendway weirs) or extreme (jetties) changes in velocities throughout the inlet system. This comparison of gray and green coastal protection interventions in tidal inlets serves as an example to contrast the effectiveness of different coastal protection alternatives at reducing erosive flow velocities and to inform alternative selection at other inlet systems.

Modeling velocity in a compound channel with co-existing emergent and submerged vegetation

Vegetation on a floodplain, which contains both emergent vegetation and submerged vegetation, has a considerable influence on the velocity profile of the channel. In this study, a modified analytical model, which considers interactions within the vegetation, is developed based on the Shiono and Knight method (SKM) and the concept of the two-layer model to obtain the transverse distribution of the depth-averaged streamwise velocity in a compound channel with emergent and submerged vegetation. This analytical model includes the influence of secondary flows, lateral shear stress, bed friction, and the drag force caused by the vegetation. The aforementioned model is then employed in a straight compound channel, which contained various types of vegetation. Using suitable boundary conditions, the calculated data are found to be consistent with the experimental data. Subsequently, the effects of dimensionless eddy viscosity coefficient (λ), the depth-averaged secondary flows coefficient, and the impact coefficient β on the model are analyzed. It finds that the λ has a clear effect on the main channel region, but the depth-averaged secondary flows coefficient (K¯) has only a definite effect in the slope sub-region. The β value is significantly less than 1 for the condition of the vegetation with a variable frontal width. The model proposed in the present work can provide a guidance for the investigation of the flow characteristics of the various vegetated channel.

Distributed Cooperative Surrounding Control for Mobile Robots With Uncertainties and Aperiodic Sampling

In this paper, we present a distributed cooperative surrounding control for mobile robots with uncertainties and aperiodic sampling. At the kinematic level, a cooperative circumnavigation guidance law with the capability of spatial-temporal decoupling, employing a line-of-sight (LOS) principle to accomplish closed orbit following and a path parameter synchronization to assign the desired speed, is devised to generate reference velocity and angular rate. At the kinetic level, to reduce the transmission burden in sensor-to-controller channel and compensate for the total uncertainties existing in velocity channels, aperiodic sampling based extended state observers (AS-ESOs), are developed to provide precise disturbance estimates with guaranteed convergence, while a nonnegative threshold-based event-triggering condition with a straightforward tuning procedure is designed to schedule the communication frequency without inducing Zeno behaviors. Then a robust anti-disturbance kinetic control protocol is synthesized that renders an equiangular distribution along the common circle. The salient merit is that a symmetric formation pattern over a closed curve defined by parameterized path, instead of time-related functions, can be obtained in a distributed manner with decreased sampling cost and disturbances. Moreover, all error variables in the closed-loop system are demonstrated to be bounded. Finally, the effectiveness of algorithm is verified by simulations.

Flow Resistance in Very Rough Channels

AbstractFlow resistance in open channels determines the average flow velocity in a river, with important implications for downstream and at‐a‐station hydraulic geometry and sediment transport in natural channels. However, flow resistance in steep mountain channels is challenging to understand and predict due to heterogeneous channel morphology and spatially variable flow. Using a double‐averaging approach appropriate for very rough channels, the width, reach, and double‐averaged variables for steady, uniform flow in an open channel are derived. Using an empirical model for the coefficient of form drag, a flow resistance model is derived that compares well to a large data set of flow velocity in natural channels. Several parameters that together describe bed morphology are observed to be relatively consistent in the data set used and compare well to previous estimates of their values. This implies a degree of self‐organization in bed morphology that may simplify the challenging problem of predicting flow resistance in steep mountain rivers.

To the Theory of Grain Motion in an Uneven Air Flow in a Vertical Pneumatic Separation Channel with an Annular Cross Section

The possibilities of the action of uneven air flows on the grain material in the separating channels are still not used enough. The reason for this is the insufficient knowledge of the processes of interaction of the components of the grain material with an uneven air flow. The purpose of the research is to increase the efficiency of grain material separation according to aerodynamic properties by purposefully changing the diagram of air velocities in the channel sections using the actions of lateral and aerodynamic forces. The separation efficiency of grain material components was determined by trajectory analysis. The different geometry of the pneumatic separation channel was studied. The study of the distribution of air velocity and air pressure vectors in a vertical annular channel was carried out using the FlowVision software. It has been established that a change in the air velocity diagram can be implemented both by changing the geometric parameters of the channel and by additional distributed air supply through the perforation in the side walls of the pneumatic channel. Based on the analysis of the velocity field, an improved scheme of a pneumatic gravitational separator is proposed for separating grain material into three fractions according to aerodynamic characteristics.

Generalized correlation for onset flooding velocity in vertical channels

Flooding due to gas-liquid counter-current flow might significantly impact engineering applications such as boilers, heat exchangers, and nuclear reactors. Despite the extensive body of literature, there is still a notable disagreement on the appropriate definition of the characteristic length regarding the onset flooding velocity in rectangular and annular channels. The primary motivation for this study is to examine which geometric dimension is the most suitable to predict the onset of flooding velocity. This study measured the onset of flooding velocity in one circular and two different annular channels. The channel geometries are considered such that the hydraulic diameter trend is inverse to the average circumference. The study's findings show that the hydraulic diameter cannot be used as a characteristic length for annular and rectangular channels to describe the onset flooding velocity. Instead, the average circumference for the annular channel and channel width for rectangular channels exhibit superior performances. The flooding air velocity was increased by increasing the average circumference of the annular channel or channel width for the rectangular channel. New Wallis-type generalized relationships are derived based on the wide range of channel geometries and dimensions. The novel generalized empirical correlation could be defined regardless of the channel geometry.

GASP XXXIX: MeerKAT hunts Jellyfish in A2626

ABSTRACT We present MeerKAT H i observations of six jellyfish candidate galaxies (JFCGs) in the galaxy cluster, A2626. Two of the six galaxies JW100 and JW103, which were identified as JFCGs from B-band images, are confirmed as jellyfish galaxies (JFGs). Both of the JFGs have low H i content, reside in the cluster core, and move at very high velocities (∼ 3σcl). The other JFCGs, identified as non-jellyfish galaxies, are H i rich, with H i morphologies revealing warps, asymmetries, and possible tidal interactions. Both the A2626 JFGs and three other confirmed JFGs from the GASP sample show that these galaxies are H i stripped but not yet quenched. We detect H i, H α, and CO(2-1) tails of similar extent (∼50 kpc) in JW100. Comparing the multiphase velocity channels, we do not detect any H i or CO(2-1) emission in the northern section of the tail where H α emission is present, possibly due to prolonged interaction between the stripped gas and the intracluster medium. We also observe an anticorrelation between H i and CO(2-1), which hints at an efficient conversion of H i to H2 in the southern part of the tail. We find that both ram-pressure stripping and H i-to-H2 conversion are significant depletion channels for atomic gas. H i-to-H2 conversion is more efficient in the disc than in the tail.

Experimental investigations of open-channel flow and velocity to develop a predictive tool from a laboratory small scale to real-world large scale

Open channel flow and velocity behaviour presents a dilemma for drainage systems designers where hydrologic parameters are fluctuating in space and time. The experience of having extreme flash floods almost every year is flustering the need for understanding the flow behaviour at different altitudes. In this study, open channel experimental efforts were made to model flow and velocity profiles. The three-dimensional (3D) open channel flow and velocity profiles are generated at two types of roughness namely steel (smooth) and concrete (rough beds). The experiments included different slope gradients and flow measurements at different distances. The channels slope ranges between 0 and 4.7% with an interval of 0.2%. Multiple linear regression (MLR) was applied to quantify the flow for longer distance while Kriging extrapolation proxy was used to generate 3D surfaces of flow and velocity. The results showed that the flow in concrete channel is decreasing by moving to the end of channel due to higher frictional resistance while it is rising up for the steel channel. In average, the velocity has been increased by 7.4% for steel and 6.1% for concrete channels at a changing slope.

Numerical Simulation Research on the Diversion Characteristics of a Trapezoidal Channel

Open-channel bifurcations are the most common water diversion structures in irrigation districts. In irrigation water conveyance, water transport efficiency and sedimentation are primary concerns. This study accordingly analyzes the influence of open-channel bifurcations on water delivery in irrigation areas. Herein, the three-dimensional flow at an open-channel bifurcation was studied via numerical simulations using FLOW-3D software and including 15 sets of working conditions. The hydraulic characteristics of the recirculation zone and flow structures in the vicinity of the open-channel bifurcation were analyzed. Equations for the flow diversion width of the surface and bottom layers in the trapezoidal channel were then obtained. The flow diversion widths along the water depth were found to differ between trapezoidal and rectangular channels. The results also show that open-channel bifurcations considerably influence the flow velocity in the main channel. The flow velocity in the recirculation zone of open-channel bifurcations was small, but the pulsation velocity and the turbulent kinetic energy were large. The energy dissipated in this area was relatively large, which was not conducive to channel water delivery. This study provides a reference for channel optimization and operation management in irrigation districts.

Study on the Performance of the Low-Cost Cooling System for Transmit/Receive Module and Broadening the Exploitative Capabilities of the System Using Gravity Heat Pipes

Abstract The authors use computer simulation and experiment to study thermal characteristics of a less expensive design of the air cooling system for transmit/receive modules based on the heat sink with the dimensions of 25 × 324 × 500 mm made of mass-produced heat sink profile. The total power of the 8 transistors in the transmit/receive module is 224 W. It is shown that the increase in air velocity in the heat sink channels from 1 to 30 m/s causes an approximately twofold drop in the maximum temperature of the mounting surface (from 78.45 to 38.70 °C) and a decrease in thermal resistance of the cooling system by 3.16 (from 0.262 to 0.083 °C/W). The air velocity range from 5 to 10 m/s proves to be the most rational option. For the inlet air temperature of 20 °C, the temperature in the spots where the transistors are mounted remains below 56.3 °C for the air velocity of 5.5 m/s in the heat sink channels and below 51.8 °C for 10.5 m/s. A new original technical solution based on low-cost flat gravity heat pipes with a threaded evaporator will provide the efficiency of the cooling system at higher inlet air temperatures.

Modeling of velocity and shear stress profiles in the ecological channel with floating vegetation.

Floating vegetation occurs in various environments, such as artificial floating islands, wetlands, river courses, and lakes, which constitute an important part of the river landscape and ecological restoration. The vertical distribution of the streamwise velocity of the channel flow with floating vegetation is of the utmost importance, and therefore, it is the basis for research on bed erosion and pollutant transport. Laboratory experiments on an open-channel flow covered by floating vegetation with unanchored roots have shown a two-layer structure of the velocity profile and a rapid decrease in the Reynolds stress across the interface in the vegetation layer but gradual in the non-vegetation layer. The flow was divided into four subzones in a vertical direction according to the organized flow structure in the experiment as follows: (I) the uniform region deep within the non-vegetation layer, (II) the outer region in the non-vegetation layer, (III) the inner region in the vegetation layer, and (IV) the uniform region deep within the vegetation layer. An analytical model based on the momentum balance in each subzone was developed to predict the profiles of velocity and Reynolds stress. The predictions from analytical models agree well with those from laboratory studies of floating vegetation and lay the theoretical foundation for future studies on water eutrophication and the transport of pollutants, sediments, and algae.

Self-Temperature Compensated Water Level and Velocity Sensor Based on Fiber Bragg Gratings

This work proposes a fiber Bragg gratings (FBG) sensor for simultaneous measurements of water level, velocity, and temperature in open channels. The optical fibers are placed on a rectangular aluminum rod attached to the bottom of the channel. The water flow causes a distributed load and a characteristic bend in the rod, depending on the water level and velocity. A set of four FBGs are used to monitor the rod’s bending profile. Taking the wavelength difference of two FBGs makes it possible to eliminate the temperature effect and obtain a system of nonlinear equations dependent on velocity and water level. Velocities from 0.1 ms to 0.9 m/s and water levels from 0.4 m to 0.7 m were experimentally evaluated. A semi-empirical model was obtained to describe the wavelength shift, and finally the water level and velocity are calculated. The results show that the proposed system can determine the water level, mean velocity and temperature with satisfactory accuracy. Artificial neural networks are used as a second and more straightforward approach to determine the water level and velocity from the measured wavelengths, considering mean values and standard deviation. With this method, the maximum absolute deviations were 0.02 m/s and 3.1 cm, for the mean velocity and water level, respectively.

Determining the Flow Resistance of Racks and the Resulting Flow Dynamics in the Channel by Using the Saint-Venant Equations

Racks retain debris in wastewater treatment plants and shield sensitive machinery in numerous engineering applications. In open-channel flows, racks impound the upstream water level by posing local obstacles in the flow. Based on experimental investigations, empirical approaches usually predict the flow resistance by relying on Bernoulli’s energy principle. Since this principle does not correctly consider downstream conditions such as submerged flows, we present a more accurate workflow to determine the flow resistance based on the Saint-Venant equations. We will demonstrate how the loss coefficient and the hydraulic head loss are determined more reliably without adding complexity to the engineering realisation. In contrast to relying solely on two cross-sections with Bernoulli’s energy principle, applying the Saint-Venant equations enables determining the flow depth profile and the flow velocity in the entire channel. This workflow additionally allows predicting the channel’s hydraulic capacity and freeboard in arbitrary applications.

Streamflow Measurement Using Mean Surface Velocity

This study developed an efficient discharge measurement method that can be applied to estimate the streamflow of natural streams and artificial channels. The conventional methods that apply current meters to measure discharge are costly, time-consuming, and labor-intensive. Owing to a shortage of observers in streamflow measurement and for the safety of hydrologists and with advances in measurement techniques, many have strongly suggested the use of non-contact methods when determining streamflow. The non-contact methods that use floats or surface velocity radar to determine the streamflow are becoming more and more popular especially during periods of high water. However, it is not easy to estimate the surface velocity coefficient of each vertical directly for determining the mean velocity in each subsection. As the relationship between the mean surface velocity and mean velocity of a stream cross-section is constant, an efficient and accurate non-contact method of streamflow measurement could be further developed. Thus, streamflow can be estimated by the constant, the mean surface velocity, and cross-sectional area of a stream. The mean velocity of a cross-section, used for parameter calibration, is usually obtained from the discharge made based on the velocity-area principle and cross-sectional area. The surface velocity was measured at the vertical that is then used to estimate mean velocity of a subsection. Once the parameter is determined, streamflow can be obtained from the surface velocity. This approach was further applied to a natural stream and an artificial channel. Measurements were made to verify the reliability and accuracy of the proposed approach. The results show that the relationship between mean channel velocity and mean surface velocity is very stable in both a natural stream and an artificial channel because the streamflow differences, given by the proposed and the conventional method, are relatively insignificant. As a result, mean surface velocity can be used to determine the streamflow quickly and provides for a reliable and accurate measurement of streamflow.