Search

The hydraulic performance and fish guidance efficiency (FGE) for behaviourally-based mechanical fish guidance structures, i.e. louvers and modified angled bar racks (MBRs), were evaluated experimentally and the results are presented herein. Detailed velocity profiling was conducted to assess the hydraulic performance of the 1:1 Froude-scaled racks in an etho-hydraulic laboratory flume. Guidance efficiencies of the studied rack configurations were evaluated through live-fish tests in the same flume. Tests were conducted with five European fish species, namely, barbel (Barbus barbus), spirlin (Alburnoides bipunctatus), European grayling (Thymallus thymallus), European eel (Anguilla anguilla) and brown trout (Salmo trutta). The results demonstrate that MBRs are advantageous over louvers because of reduced head losses, improved hydraulics and higher FGEs. Furthermore, use of a bottom overlay on the MBRs substantially increased the FGE. The results are discussed and compared with literature data. Recommendations for an optimized and economic MBR design are given. The present findings underpin the follow-up studies for further optimization of MBR design. [ABSTRACT FROM AUTHOR]

Abstract Trash screens are widely employed at entrance of hydraulic structures (culverts, barrages..., etc.), water intakes, and pumping stations to trap flowing debris that could instigate downstream troubles. Traditional trash screen (perpendicular-vertical screen to the flow direction) can cause problems of increasing head loss through it, especially with the blockage ratio. This experimental study presents a concept of an adjusted screen with circular bars to find a solution for such problem. In this regard, angled screen models with different angles, blockage ratios, and flow discharges were investigated. The results indicated that the head loss coefficients reduced by reducing the screen angle, so angled screen (α < 90°) reduced the loss in comparison with the traditional trash screen (α = 90°). The values of head loss coefficient increased with increasing blockage ratio, and flow discharge. The screen losses increase strongly when the screen becomes blocked by 40% or more. Screen angle, blockage ratio, and discharge influence effectively the head loss of a screen. Furthermore, a new equation for the head loss, the key element in designing screens, is proposed based on the different tested parameters, and should be useful in designing trash screens. [ABSTRACT FROM AUTHOR]

ABSTRACT Chun, I.; Kang, H., and Lim, H.S., 2018. Revisiting Head Loss of the Perforated Wall with Vertical Slits. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1056–1060. Coconut Creek (Florida), ISSN 0749-0208. A theoretical analysis and hydraulic experiments were performed to investigate the head loss that occurs when a flow passes through a perforated wall with vertical slits. In the theoretical analysis, continuity and energy equations were applied to a control volume set near the perforated wall. A non-dimensional energy equation was then derived to calculate head loss for the given values of the ratio of upstream and downstream depths and a Froude number based on downstream depth and velocity. The hydraulic experiments were performed by varying flow condition and the opening ratio of perforated walls. The non-dimensional energy equation and experimental results were finally used to evaluate the accuracy of three existing formulas. [ABSTRACT FROM AUTHOR]

Copyright of Revista Brasileira de Engenharia Agricola e Ambiental - Agriambi is the property of Revista Brasileira de Engenharia Agricola e Ambiental and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To determine the conditions under which a pumped-storage power plant (PSPP) requires a tailrace surge chamber and to account for the time sequence superposition of water hammer vacuum, velocity head vacuum and head loss vacuum, we derived a new setting criterion using the rigid water hammer theory. Next, several setting criteria of tailrace surge chambers are investigated, and comparisons among them are conducted for certain PSPPs. The results show that the critical length of tailrace system (CLTS) calculated by the Chinese empirical discriminant are much larger, resulting in an adverse impact on safe operation; according to the American empirical discriminant, Tongbai and Heimifeng PSPPs with large safety margins in the draft tube need to set up the tailrace surge chambers, leading to unnecessary waste; for Tongbai and Yixing PSPPs with large differences in head loss and guide vane closing law, only 5–8 m difference in CLTS is acquired based on the Japanese empirical discriminant, which is not practical; the discriminant results obtained by the new setting criterion are consistent with the actual setting conditions, and it is more realistic to incorporate the effective closing time of guide vane and the relative head loss coefficient into the influencing factors. [ABSTRACT FROM AUTHOR]

Scale effects and hydraulic head losses are systematically investigated for fish guidance structures, i.e. louvres and angled bar racks. The experiments were conducted at 1:1 and 1:2 Froude-scaled models in a laboratory flume for a wide range of rack configurations under various hydraulic conditions. The study involves three main rack angles, three bar angles, and three bar openings as primary parameters characterizing the structure investigated, and two bar shapes, three bar depths and three relative rack submergences as secondary parameters. This study demonstrates that the above parameters are strongly interrelated with respect to the head loss, and the bar opening has a determinative effect on the flow-rack interactions. The analysis of functional relations among the parameters has led to a new head loss prediction formula. The implications of the findings for optimum engineering solutions in terms of head loss, fish guidance and project economy are also addressed. [ABSTRACT FROM AUTHOR]

The optimization of a water distribution system (WDS) is challenging because of its nonconvex head loss constraint. To address this issue, this paper proposes a modeling technique to represent the nonconvex head loss equation by convex constraints. In the convexification, the head loss equation is first rewritten into nonlinear inequalities, then disjunctive programming is used to represent the flow direction and pipe selection. The technique is applied to formulate a convex mixed-integer nonlinear programming (MINLP) model for WDS design. Effectiveness of the convexification is demonstrated by several benchmark examples. [ABSTRACT FROM AUTHOR]

This paper proposes a new model to determine the head losses at confluences in one-dimensional models of open channel networks, making use of a momentum conservation approach. Momentum conservation has been applied in several theoretical models for confluence head losses, giving satisfactory results in general. However, for larger confluence angles between the main channel and the incoming tributary, the model accuracy diminished. Many authors identified that a correct estimation of the tributary momentum contribution is a prerequisite for accurate results. This work reports on the development and application of a theoretical model for the tributary momentum contribution, based on similarities with the flow upstream of a circular bend in a straight open channel. It describes the two-dimensional depth-averaged flow features in the tributary under the assumption of a 90° angle confluence in which all channels have equal widths, in order to obtain the resulting momentum contribution. The proposed model predicts head losses within the same order of accuracy as a numerical model solving the shallow water equations in two dimensions throughout the confluence. [ABSTRACT FROM PUBLISHER]

Air can be entrapped in water and wastewater systems under a variety of conditions, and if such air is not managed properly, it can impose considerable operational penalties. To avoid these problems and the dangers associated with air pockets, several air management strategies have been routinely suggested. However, the devastating consequences of air pockets frequently documented in the literature imply the need for further development in this area. Improving air management obviously requires a thorough understanding of the current strategies and their shortcomings. This paper overviews the sources of air in pipes and key consequences associated with its presence. Current measures for managing air in water pipes are reviewed and critiqued. Finally, knowledge gaps that limit the efficient application of current air management strategies to real world problems are identified, and suggestions for future development are presented. [ABSTRACT FROM AUTHOR]

The use of portable short-throat flume in the field is an emerging technique developed for water discharges measurement of inlet in the field. Based on the principle of critical flow and RNG k – ε three-dimensional turbulence model along with the TruVOF technique, experiments and corresponding simulations were performed for 16 working conditions on the 76 mm width flume with discharges up to 40.01 L/s to determine its hydraulic performance. Hydraulic performance of the flume obtained from simulation analyses were later compared with observed results based on time-averaged flow field, flow pattern, Froude number and velocity distribution. Comparison yielded a solid agreement between results from two methods with relative error below ±10%. Regression models developed for upstream depth versus discharge under different working conditions were satisfying with the relative error of 9.16%, which met the common requirements of flow measurement in irrigation areas. Compared to the long-throat flume, head loss of portable short-throat flume in the field was significantly less. Further, head loss under the free flow condition was less than that under the submerged flow condition of portable short-throat flume with a flat base in the field. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article refutes theoretical arguments that it is inexpedient to increase gas pressure in a blast furnace as a means of intensifying the smelting operation. The intensifying effect of higher gas pressure has been proven by the results obtained on three blast furnaces at the Novolipetsk Metallurgical Combine. The productivity of these furnaces increases by 0.7-1.2% for each 1% rise in top-gas pressure within the range 38-40%. It has been established that the increase in productivity is accompanied by an increase in head loss for the furnace as a whole. Head losses also increase by a ratio of 0.8:0.2 in the top and bottom of the stock, respectively. [ABSTRACT FROM AUTHOR]

Two equations for computing head loss in self-cleaning screen filter when using tap water and sand water mixture were developed using dimensional analysis. The parameters influencing head losses were considered to be eleven parameters representing the filter properties; filtration level, total filtration surface, flow rate, concentration of total sand, filtration time, inside diameter of the inlet and outlet pipes, mean filtration velocity, mean diameter of sand particle size distribution, water viscosity and water density. These variables were incorporated into eight dimensionless groups obtained through Buckingham's method. Two experiments to analyse head losses were carried out using 178 μm and 124 μm screen filters. A total of 54 runs for tap water and 58 filtration cycles for sand water mixture were carried out to obtain 54 and 2152 experimental points respectively, enabling the developed equations to be correlated. The developed equations were satisfactorily adjusted using the experimental data. Despite the adjustments of the equations being significant, regression coefficients were not always high. A comparison between the predicted and the measured head losses with three screen filters was in close agreement with a correlation coefficient of 0.902 for tap water and 0.832 for sand water mixture, respectively. The performance of equation was also compared with equations developed from the literature. The equations from Puig-Bargués et al. (2005b ) Biosystems Engineering, 92 (3), p383–390 and this study provided good predictions, compared to other equations available in the literature. [ABSTRACT FROM AUTHOR]

Within the Zufiria’s potential flow theory generalized by Sohn (2007), we investigate the effects of head loss on the growth of the Rayleigh–Taylor and the Richtmyer–Meshkov instabilities. The nonlinear asymptotic solutions including the effects of head loss are obtained analytically for the bubble amplitude, velocity and curvature. We find that head loss depresses the bubble amplitude and velocity but enhances the bubble curvature. With an increase in the loss coefficient ζ , the bubble amplitude and velocity decease rapidly, whereas the bubble curvature increases rapidly. A maximum of ζ is found for the Rayleigh–Taylor instability, i.e., ζ → ζ max = 0.5 which is independent of the Atwood number A . But for the Richtmyer–Meshkov instability, ζ max depends on the Atwood number and ζ max = 0.625 - 0.875 for A = 0 - 1 . Our results of the bubble amplitude are found to be in good agreement with experimental data when we choose the suitable loss coefficients. [ABSTRACT FROM AUTHOR]

Abstract: Fibrous porous media have been studied in diverse engineering fields. In nuclear power plants, fibrous debris produced during the blow-down phase of Loss of Coolant Accidents (LOCA) is transported into the sump and becomes an important cause of head loss through the sump strainer affecting the Emergency Core Cooling System (ECCS) performance. In this study, a vertically installed strainer plate in a horizontal pipe flow loop was designed to generate fibrous beds on the strainer and permit measurement of the head loss through the beds. NUKON fibrous insulation material was used as the fibrous debris prepared by shredder method explained in NUREG/CR-6224 report. The head loss data with the shredder method was mainly analyzed considering porosity and fibrous bed thickness. A modified head loss model was suggested and compared to the head loss models developed in previous studies. [Copyright &y& Elsevier]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Experimental results for fish-friendly trashracks placed in an open-water channel are presented. Eighteen angled trashracks were used to test different bar spacings, bar shapes and rack angles. Each model trashrack comprised two horizontal supports with regularly spaced slots adjusted to compensate for the trashrack angle, i.e. maintain the vertical bars “streamwise” (parallel to flow). Water depths and velocity profiles were acquired upstream and downstream of each rack configuration. The results reveal that the head-loss coefficient for angled racks with streamwise bars does not depend on the rack angle and can be calculated with equations for racks perpendicular to the channel. Upstream velocity profiles along the rack are not significantly affected by the rack angle and downstream transverse profiles are nearly uniform. A comparison with conventional angled trashracks with bars set perpendicular to the rack revealed the many advantages of streamwise bars. [ABSTRACT FROM AUTHOR]

Case studies of energy loss over bed forms in gravel-bed rivers are needed to determine local loss coefficients for modeling and design. In this study, an intense field campaign in two rivers is used to determine energy loss and calculate local energy loss coefficients () for riffle-pool units. Velocity head, water surface elevations, and energy coefficients () are determined at up to eight cross sections at each site over a range of discharges including, at one site, the bank-full discharge. The water surface and energy grade line are relatively flat as flow enters the pool and relatively steep as flow leaves the pool. In both watercourses and at all discharges, is higher in pools (i.e., velocity is more heterogeneous) and lower in riffles (velocity is more homogeneous). In a short but deep pool forced by a large fallen tree (Moras Creek), . This high value is explained by a pool obstruction that results in a series of gradual and sudden flow transitions. In a long and relatively shallow pool (Ditton River), . This low value is explained by the uncertainty in resistance partitioning and the variability of models for skin friction. Future research should determine the range of local energy loss coefficients in natural and constructed bed forms in rivers. [ABSTRACT FROM AUTHOR]

The relationship between the head loss and the discharge and circulation of the conduit of a pump system with low head is an important problem with an obvious influence on the improvement of its hydraulic performance. The velocity circulation from the pump guide vane makes the relationship more complicated, which has to be understood comprehensively. The results indicate that, under the condition of zero circulation, the head loss of the inlet and outlet conduits is in proportion to the square of discharge. Under the condition that the Reynolds number is satisfied with the resistant square area, the conduit loss is in proportion to the square of discharge for the similar working points with different speeds in a certain rotational speed range, indicating that the pump system efficiency is constant. The outlet conduit loss of design discharge for a pump system with low head depends on the velocity circulation from the guide vane exit, and the relationship between the loss and the circulation is an open curve with an upward direction, meaning that there is an optimal circulation for the loss. Under the condition of various working points for a pump system with low head, the head loss of the outlet conduit is under the cross influence of both the discharge and the circulation. As a result, the relationship between the head loss and the discharge is almost linear, and the mechanism needs to be further studied. [ABSTRACT FROM AUTHOR]

Through an analysis of the head loss of the gas–liquid two-phase flow in a siphon pipe, this paper measures the bubble velocity, pressure drop, and gas fraction under various conditions. The influence of varied head, gradient, and installation heights of the pipe on the air mass movement, head loss, and resistance coefficient of the gas–liquid two-phrase flow is analyzed on the basis of the test results. The results show that the bubble velocity reaches its minimum on the flat slope, and the velocity on the positive slope is higher than that on the reverse slope. The head loss of pipelines in both the positive slope and reverse slope increases as the gradient increases, while the head loss on the reverse slope is larger than that on the positive slope under the same gradient. When the gas fraction α is between 8% and 30%, the resistance coefficient λm is related to the gradient, gas fraction, and the Reynolds number Re. Furthermore, λm is proportionate to α and inversely proportionate to i of the bottom slope and the Re number. The calculation formula of the resistance coefficient λm under various gradients within the scope of the above gas fraction is derived on the basis of the test data, while the relative error is controlled within the allowable range. [ABSTRACT FROM AUTHOR]

The requirements for fish protection at hydro power plants have led to a significant decrease of the bar spacing at trash racks as well as the need of an inclined or angled design to improve the guidance effect (fish-friendly trash racks). The flexible fish fence (FFF) is a new developed fish protection and guidance system, created by horizontally arranged steel cables instead of bars. The presented study investigated experimentally the head loss coefficient of an angled horizontal trash rack with circular bars (CBTR) and the FFF with identical cross sections in a flume (scale 1:2). Nine configurations of different bar and cable spacing (blockage ratio) and rack angles were studied for CBTR and FFF considering six different stationary flow conditions. The results demonstrate that head loss coefficient is independent from the studied Bar–Reynolds number range and increases with increasing blockage ratio and angle. At an angle of 30 degrees, a direct comparison between the two different rack options was conducted to investigate the effect of cable vibrations. At the lowest blockage ratio, head loss for both options are in similar very low ranges, while the head loss coefficient of the FFF increases significantly compared to the CBTR with an increase of blockage. Further, the results indicate a moderate overestimation with the predicted head loss by common head loss equations developed for inclined vertical trash racks. Thus, an adaption of the design equation is proposed to improve the estimation of head loss on both rack options. [ABSTRACT FROM AUTHOR]

Irrigation channels need expansions to provide a cross-sectional transition. Expansions often cause flow separation, turbulent eddy motions, channel erosion, and flow energy dissipation. The purpose of this paper is to investigate the effectiveness of fitting a hump at the expansion's bottom in reducing flow separation and energy loss. This paper reports analytical solutions to the problem of flow transition and associated energy head loss, by using the momentum and energy concepts complementarily, as well as experimental results for verifying the solutions. The use of a triangular hump can effectively reduce head loss; the head loss coefficient drops by a factor of up to 4. The mechanism at work is that the presence of a hump forces the flow to accelerate, neutralizes the decelerating effects of expanding width, and creates favorable pressure gradients working against flow separation. Humps with a crest height of 5-9% of the depth of approach flow are recommended, with a good potential to save a substantial amount of flow energy. Researchers can easily incorporate such humps into existing expansions. [ABSTRACT FROM AUTHOR]

Former studies on combining flows resulted in an efficient layout of sewer junctions operated under supercritical approach flow conditions. Straight extensions allowed a reduction in the shock wave heights generated by the merging flows, so that the global discharge capacity was significantly increased. Herein, an extensive experimental campaign is presented on a physical model with the aforementioned layout, although with generalized geometrical conditions now including various conduit diameters. The effects of the main parameters governing the energy losses for combining flows were ascertained to enhance the information available from the literature. The results and their analysis provide a basis for the prediction of energy losses at junction manholes with different upstream and lateral conduit diameters and various flow conditions. [ABSTRACT FROM AUTHOR]