Rectangular Open Channel Research Articles

Theoretical and experimental investigation of a lateral broad-crested contraction as a flow measurement device

The article looked at the possibility of making use of a lateral contraction as a flow measurement device in a rectangular open channel. The contraction under consideration consisted of two removable prismatic elements placed on either side of the walls of the channel. This configuration resulted in the creation of a throat of length L and opening width b less than the channel width B so that the contraction rate has been defined as β = b/B. This ratio actually reflects the degree of the lateral contraction while there is no vertical contraction because the device is devoid of crest height. Its longitudinal axis thus merges with that of the channel, which gives the device a self-cleaning property. Due to the changeover of the subcritical flow upstream of the device to a supercritical flow inside the throat, firmly confirmed by laboratory observations, a control section has been created in a given section at the entrance of the throat. This is the prerequisite for the correct functioning of a flow measuring device in open channels.The essential steps undertaken during the study were firstly the research for the theoretical relationship governing the flow rate Q for forthwith deriving the resulting discharge coefficient Cd equation. This aim has been successfully achieved through the simultaneous application of the momentum and the energy equations taking care to include the effect of the approach flow velocity. The obtained theoretical flow rate QTh was identified in the form of explicit functions depending both on the geometric characteristics of the device and the upstream depthh1 which is fully consistent with semi-modular devices. Likewise, the resulting discharge coefficient Cd,Th was formally identified as being exclusively dependent on the contraction rate β and this finding was predicted by the dimensional analysis.The statistical analysis of the 157 collected experimental values allowed observing an excellent agreement between the theoretical and experimental discharge coefficients. The maximum deviation calculated over the tested range of β was only 1.22%. The use of linear least-squares fitting method involving experimental and theoretical data gave the following trend line relationship Cd,Exp=0.9911Cd,Th obtained with a coefficient of determination R2=0.9906. Thereby, using the previous equation, the accuracy on the discharge coefficient Cd,Th computation has been highly improved since the maximum deviation reduced to only 0.66%.

Influence of distance from water surface of a horizontally installed Savonius turbine in a rectangular open channel on turbine performance

Abstract The aim of this investigation is to develop a nano-hydro turbine that can effectively utilize the wasted hydraulic energy in infrastructure such as agricultural and industrial canals and irrigation waterways. Up to this time, the utilization of such a small hydropower has not progressed owing to economic reasons. Therefore, we focus on the Savonius type, which has the advantages of low manufacturing cost and excellent maintainability because of its simple structure. Conventionally, the Savonius type has been developed and researched as a vertical axis wind turbine. In order to effectively utilize the water surface flow, which is particular to open channels, we place the turbine runner perpendicular to the water flow and horizontally on the channel bottom. In the present study, we experimentally investigated the effect of the parameters for the turbine installation and its operation, namely distance between a runner and the water surface and the rotation direction of the runner, on the performance at each water level. As a result, it was found that the suitable installation depth differs depending on the rotation direction of the turbine.

Flow dynamics in lateral vegetation cavities constructed by an array of emergent vegetation patches along the open-channel bank

The hydrodynamics in a straight rectangular open channel containing novel lateral cavities constructed by an array of square emergent vegetation patches discontinuously distributed along the bank were explored numerically using three-dimensional large eddy simulations (LES). Five vegetation densities (Φ), ranging from 0.02 to 0.25, as well as the traditional lateral cavities created by impermeable solid media, were tested. The effects of the cavity aspect ratio (AR) were also examined. The LES results showed that the mean recirculation pattern inside the vegetation cavities and coherent structures in the horizontal shear layer were closely dependent on Φ and AR. When Φ ≥ 0.06, a main recirculation vortex that formed inside the vegetation cavities resembled that within solid media cavities, whereas the extent of the former increased upstream as Φ increased. Compared with the solid cases, the vegetation cavities exhibited a higher turbulent intensity within the shear layer and wider regions of enhanced turbulent kinetic energy, which decreased with increasing Φ. The penetration depth of the elevated turbulent kinetic energy into the cavities also decreased with increasing Φ, whereas a deeper penetration was expected at larger AR values. The interfacial turbulence was dominated by “cavities field”-scale coherent vortices at Φ ≤ 0.06, whereas “cavity element”-scale at Φ ≥ 0.15. When Φ = 0.1, the shear vortices of both scales contributed to the enhancement of the interfacial turbulence. The mean mass exchange showed a non-monotonic relationship with Φ and reached maximum values at Φ = 1. The total momentum transport efficiency decreased monotonically with increasing Φ. Despite the AR and Φ values, the turbulent motions dominated the momentum transport over most of the cavity length.

Cooling Performance of Additively Manufactured Pin Fins in Stacked Microchannels for the Inside-Out Ceramic Turbine Shroud-Cooling Ring

Abstract The inside-out ceramic turbine (ICT), a novel microturbine rotor architecture, has an air-cooled ring, which keeps its composite rotating structural shroud within operating temperature. The cooling ring must achieve a significant radial temperature gradient with a minimal amount of cooling. The cooling ring is made through additive manufacturing, which opens the design space to tailored cooling geometries. Additively manufactured pin fin heat transfer enhancers are explored in this study to assess whether they hold any significant performance benefit over current rectangular cross section open channels. Experimental friction factors and Nusselt numbers were determined for small, densely-packed pin fins over an asymmetrical thermal load. Results indicate that pressure loss is similar to what can be expected for additively manufactured pin fins, whereas heat transfer is lower due to the extremely tight streamwise pin spacing, in both in-line and staggered pin configurations. A design study presented in this article suggests that pin fins are beneficial to an ICT for reducing cooling mass flowrate up to 40%, against an increase in cooling ring mass of roughly 50%.

Characteristics of a rectangular channel sensor based on evanescent field enhanced photonic crystal fiber

A miniaturized, rectangular-channel photonic crystal fiber (RC-PCF) high-sensitivity sensing scheme is proposed for high-refractive-index liquid analysis. The designed PCF is polished and features an open rectangular channel in the upper-middle part of the fiber cross-section, which facilitates the efficient flow of the sample liquid. The design utilizes the merit of photonic crystal array and the operability of external sensing. Gold is chosen as the plasma material because of its chemical stability and biocompatibility in a liquid environment. To obtain high sensitivity, the effect of the sample liquid height in the channel on the sensing performance is investigated. Numerical results show that the maximum wavelength sensitivity and amplitude sensitivity of the sensor is 28,000 nm/RIU (refractive index unit) and − 1266.5 R I U − 1 with a liquid analyte height of 100% of the channel height. The maximum wavelength sensitivity increases from 28,000 to 42,000 nm/RIU when the gold film thickness decreases from 30 nm to 20 nm. Due to the sensor’s simple structure and high sensitivity, it will have potential applications in the detection of high-refractive-index samples in biology, medicine, and chemistry.

About 3D Incompressible Flow Reconstruction from 2D Flow Field Measurements.

In this paper, an assessment of the uncertainty affecting a hybrid procedure (experimental/numerical) is carried out to validate it for industrial applications, at the least. The procedure in question serves to depict 3D incompressible flow fields by using 2D measurements of it and computing the third velocity component by means of the continuity equation. A quasi-3D test case of an incompressible flow has been inspected in the wake of a NACA 0012 airfoil immersed in a forced flow of water running in a rectangular open channel. Specifically, starting from a 2D measurement data in planes orthogonal to the stream-wise direction, the computational approach can predict the third flow velocity component. A 3D ADV instrument has been utilized to measure the flow field, but only two velocity components have been considered as measured quantities, while the third one has been considered as reference with which to compare the computed component from the continuity equation to check the accuracy and validity of the hybrid procedure. At this aim, the uncertainties of the quantities have been evaluated, according to the GUM, to assess the agreement between experiments and predictions, in addition to other metrics. This aspect of uncertainty is not a technical sophistication but a substantial way to bring to the use of a 1D and 2D measurement system in lieu of a 3D one, which is costly in terms of maintenance, calibration, and economic issues. Moreover, the magnitude of the most relevant flow indicators by means of experimental data and predictions have been estimated and compared, for further confirmation by means of a supervised learning classification. Further, the sensed data have been processed, by means of a machine learning algorithm, to express them in a 3D way along with accuracy and epoch metrics. Two additional metrics have been included in the effort to show paramount interest, which are a geostatistical estimator and Sobol sensitivity. The statements of this paper can be used to design and test several devices for industrial purposes more easily.

Uniform Flow of Molten Metals in Rectangular Open Channels

The flow of liquids in open channels has been studied since ancient Rome. However, the vast majority of published reports on flow in open channels are focused on the transport of drinking water and sewage disposal. The literature on the transport of molten metals in open channels is quite scarce. In this work, the uniform flow of pig iron and molten aluminum in rectangular open channels is studied. Specific energy curves are constructed and critical heights are analytically determined. The transition from subcritical to supercritical flow is analyzed as a function of the angle of inclination of the channel and the roughness of its walls. Manning’s equation is applied to the pig iron flow using data reported in the literature for molten aluminum. The need to correct the roughness coefficient for pig iron is observed in order to obtain results consistent with those previously reported.

Unsteady Non-Uniform Flow of Molten Metals in Rectangular Open Channels

In the metallurgical industries, it is very important to characterize the flow of molten metals in open channels given that they are transported through these devices to different plant sections. However, unlike the flow of water which has been studied since ancient times, the flow of molten metals in open channels has received little attention. The unsteady non-uniform flow of blast furnace molten pig iron in a rectangular open channel is analyzed in this work by numerical solution of the Saint-Venant equations. The influence of mesh size on the convergence of molten metal height is studied to determine the proper mesh and time step sizes. A sinusoidal inflow pulse is imposed at the entrance of the channel in order to analyze the propagation of the resulting wave. The influence of the angle of inclination of the channel and the roughness coefficient of the walls on the amplitude and the dynamic behavior of the height of the molten metal are analyzed. Phase portraits of the channel state variables are constructed and interpreted. Numerical simulations show that as the angle of inclination of the channel increases, the amplitude of the formed wave decreases. From 10 degrees onwards, the peak of the wave descends even below the initial height. On the other hand, the roughness coefficient affects the molten pig iron height profiles in an inverse way than the angle of inclination. The amplitude of the formed wave increases as the roughness coefficient increases.

Experimental investigation of scouring around a single spur under clear water conditions

Abstract This study presents the effect of different parameters on the scouring process around spur dikes. Our research group's stated objective was to evaluate the effects of sediment gradation, flow depth, spur angle and spur length on the scouring process. Since most existing studies generally employed uniform sediment, in this study uniform and non-uniform sediment were selected. Experiments were made in a rectangular open channel in uniform flow conditions. Results showed that the effect of the spur dike length and the orientation angle on sediment scour varies with the type of sediment used. Scour volumes were 40% greater in uniform sediments than in non-uniform sediments. Measured scour depth was maximum at spurs perpendicular to the flow, whereas the scour volume was maximum at spurs directed upstream. The scour depth increased with an increase in the spur length; however, the effect of spur length on scouring varied at a contraction rate of 0.29 for uniform sediments and 0.36 for non-uniform sediments. A multiple regression analysis was also performed, and four equations were suggested to predict the scour depth and scour volume. Comparisons were made with the literature equations applicable for clear-water scouring to check the suggested equation. Because of the wide range of contraction ratios considered in this study, the equations which considered the contraction effect yielded better estimates.

Calibration of Stage–Discharge Relationship for Rectangular Flume with Central Cylindrical Contraction

The design and calibration of a simple rectangular flume with central cylindrical contraction is presented. The flume is designed based on principles of critical flow in open channels. Critical flow is created through contraction of flow cross section by installing a vertical cylindrical column at the center of a rectangular open channel. The stage–discharge relationship was calibrated using a laboratory prototype with various configurations. A previously developed model was recalibrated using the laboratory data for the proposed flume. The results of the proposed stage relationship were also compared with results from a computational fluid dynamics model (CFD). The results and analysis show that if the piezometric head is measured at midstream at the upstream side of the contracting column, then stage–discharge relationship can be developed, which is independent of the contraction ratio. The stage–discharge function developed in this paper can be used for design and calibration of the flume regardless of the flume size or contraction ratio. The stage–discharge relationship equation is also compared with another set of independently measured laboratory data.

Exploring induced oscillatory free-surface waves in prismatic open-channel

This paper reported on the free-surface wave behavior in a rectangular open-channel, induced by sluice-gate maneuvers. The numerical solver was based on the (2/4)-dissipative scheme being used for the numerical discretization of the one-dimensional Extended St-Venant model embedding the Boussinesq add-on term. The numerical solver was firstly validated against experimental data and alternative numerical solver quoted in the literature. Then, the fundamental pulsation of the hydraulic system was inspected using the analogy with the water-hammer theory observed in pressurized-pipe flow. Different flow scenarios were reported; including the superposition between a downstream water-hammer maneuver and sine excitation of upstream flow depth using different pulsation values. Results highlighted that such sluice-gates maneuvers involved severe scenarios leading to significant amplification of the depth peak and crest values above the initial value.

INFLUENCE OF ROUGHTY OF A RECTANGULAR OPEN CHANNEL ON FLOW SPEEDS AND WATER FLOW

<p>This paper presents an analysis of water flow and flow velocity in an open channel of rectangular cross section as a function of channel roughness, ie Manning roughness coefficient. Three different cases of finishing the open channel of rectangular cross-section were analyzed, namely the concrete channel, the channel with smoothed cement mortar and the channel in very poor condition with shore erosion overgrown with sedges and large stones at the bottom of the channel. Analyzes were performed on a rectangular channel 3.0 m wide and with water depths in the channel from 0.5 m to 1.5 m with a step of 0.1 m, for steady flow. The longitudinal fall of the bottom of the rectangular channel in all analyzed cases was 1%.u urađene na pravougaonom kanalu širine 3,0 m i sa dubinama vode u kanalu od 0,5 m do 1,5 m sa korakom od 0,1 m, za ustaljeno tečenje. Podužni pad dna pravougaonog kanala u svim analiziranim slučajevima je iznosio 1%. The paper showed that higher Mannig roughness coefficients give lower water flow in the canal. The importance of the paper is reflected in the fact that for each of the three analyzed treatments of the rectangular channel, a quadratic function of water velocity and flow depending on the water depth in the channel was obtained. During the hydraulic calculation, the type of lining of the open rectangular channel should be taken into account in order for the dimensioned channel to be the most favorable in terms of maximum throughput.</p>

Numerical Analysis of Unsteady Laminar Flow past a Pentagonal Obstacle

The current article dispenses the numerical investigation of a two dimensional unsteady laminar flow of incompressible fluid passing a regular pentagonal obstacle in an open rectangular channel. The centre of attention of this work is the comparison of drag coefficients estimated for two distinct cases based on the orientation of face and corner of an obstacle against the flow direction. The numerical results shows that the corner – oriented obstacle bring about 42% larger value of drag coefficient at Re = 500 than face – oriented obstacle. The substantial growth in the expanse of vortex behind obstacle (presented as a function of fluid inertia 25 < Re < 500) is analyzed through the contours and streamline patterns of velocity field. The two eddies in the downstream become entirely unsymmetrical at Re = 500 for both the cases, whereas; the flow separation phenomena occurs a bit earlier in the face – oriented case at Re = 250. Two dimensional Pressure – Based – Segregated solver is employed to model the governing equations written in velocity and pressure fields. The numerical simulations of unsteady flow are presented for 50 seconds time frame with time step 0.01 by using one of the best available commercial based Computational Fluid Dynamics (CFD) software, ANSYS 15.0.

Experimental study on rectangular cut-throated flume: Effects of flume walls slopes and channel longitudinal slope

This research conducted to study the flow through a rectangular cut-throated flume (RCTF). The flume is simply formed by placing two vertical triangular prisms (two vertical folded plates) on either side of a rectangular open channel. Both channel and flume cross-sections are rectangular. The investigated flume is inexpensive, easy to install and does not require high maintenance. A wide experimental investigation, carried out under free outflow conditions and under upstream subcritical flow regime to investigate the effects of the channel longitudinal slope, the flume throat width, and slopes of upstream and downstream flume walls on the stage-discharge relationship. The stage-discharge relationships were deduced by applying the dimensional analysis and were calibrated using the data of this study. The proposed stage-discharge equation for horizontal channel has an average absolute relative error of 2.97% with the relative errors restricted in the range of ±10%, and 80% of the data points are in the error range of ±5%. The proposed stage-discharge equation for sloping channel has an average absolute relative error of 3.97% with the relative errors restricted in the range of ±10%, and 66% of the data points are in the error range of ±5%. The measurements indicate that slopes of upstream and downstream walls affect the stage-discharge relationship of the CTFs only in sloping channels and flow discharge is not influenced by the flume walls slopes in a horizontal channel. The proposed unified stage-discharge equation for both horizontal and sloping channels has an average absolute relative error of 3.38% with the relative errors restricted in the range of ±10%, and 74% of the data points are in the error range of ±5%. The proposed stage-discharge model demonstrates favorable accurate and convenient estimation of discharge for flows through the CTFs.

Critical Water Depth Features over Broad-Crested Weirs.(Dept.C)

The characteristics of flow over suppressed broad-crested weirs have been extensively studied by old and recent investigations, while for contraeled ones, the studies are limited. In the present study, the charaeteristies of the critical water depth over the contracted weirs were investigated. The effects of the different weir geometrical ratios and different flow parameters on the critical water depth locations were discussed. Experiments were conducted on a laboratory flume and the measured data were analyzed. An empirical equation, in terms of the weir and the flow parameters was developed to predict the critical water depth over the broad-crested weirs. Another empirical equation was also developed 10 predict the location of the critical water depth over such weirs. A good agreement was found between the developed equations and the experimental observations of die present study and that of others. Hence, the passing flow discharge becomes easy to be determined using one of the developed empirical equations and applying the discharge equation in terms of the esitical water depth in a rectangular open channel.

Numerical simulation of capillary flow in open rectangular channels

Numerical simulation of capillary flow in open rectangular channels

Silting thickness analysis of regular desilting in rectangular and trapezoidal channel

Silting in river is a dynamic process, so it needs to regular desilting. At present, underwater siltation monitoring is still in its early days and based on experience. This paper puts forward the criterion of discrimination, in which the flood discharge section is decreased by 20%. It used the method of steady uniform flow in open rectangular and trapezoidal channel for calculation. The results show that reference values of dredging thickness in different section forms were determined. Siltation thicknesses of rectangular channel are linearly related to water depth. And the reduction rate of trapezoidal channel has a quadratic function relation with silting thicknesses. They were proportional to channel width and their rates trended to mitigation when the bottom width and flood depth were constant. In addition, the reference value of dredging thickness should be determined by combining with the bottom width, surface width, water depth and other actual situation.

Bed and wall shear stresses in smooth rectangular channels

Various empirical equations for mean bed and wall shear stresses have been proposed for smooth rectangular open channels. Considering that the distribution of bed shear and wall shear stresses is affected by the cross-sectional shape, the gravity force based on the flow depth used to non-dimensionalize shear stresses in previous studies is modified to a parameter that includes the width and wetted-perimeter. This yields a new set of dimensionless equations for mean bed and wall shear stresses, and the wall/bed shear force ratio. These equations compared well with all available experimental data over a wide range of aspect ratios from 0.31 to 50. These equations also yield new relationships for bed and wall friction factors.

Reducing Taylor-Aris dispersion by exploiting lateral convection associated with acoustic streaming

Flow physicochemical processes, like adsorption/desorption-based separations and chemical conversions in open rectangular microfluidic channels are fundamentally limited by axial dispersion. In this contribution, the implementation of acoustics is investigated to reduce axial dispersion in microchannels. The extent of dispersion reduction is studied by means of plug injections. It was observed that the long range vortex flow of acoustic streaming can efficiently reduce dispersion by more than a factor of two. The observations made in the present study pave the way towards the development of novel, highly efficient analytical or preparative separations and microreactors with uniform residence time distributions. We elaborate on the practical implementations of both areas.

Gate-Opening Criterion for Generating Dam-Break Flow in Non-Rectangular Wet Bed Channels

A sudden dam failure is usually simulated by the rapid removal of a gate in laboratory tests and numerical simulations. The gate-opening time is often determined according to the Lauber and Hager instantaneous collapse criterion (referred to as the Lauber–Hager criterion), which is established for a rectangular open channel with a dry bed. However, this criterion is not suitable for non-rectangular channels or initial wet-bed conditions. In this study, the effect of the gate-opening time on the wave evolution is investigated by using the large eddy simulation (LES) model. The instantaneous dam-break, namely, a dam-break without a gate, is simulated for comparison. A gate-opening criterion for generating dam-break flow in a non-rectangular wet-bed channel is proposed in this study, which can be used as an extension of the Lauber–Hager criterion and provides a more comprehensive and reasonable estimate of the gate opening time.