Local Head Loss Research Articles

Flow in fracture Intersections: Deflection flow assumption reexamined

Deflection flow, which represents the process of flow redistribution at fracture intersections, is essential for accurately predicting fluid infiltration and contaminant transport in fracture networks. However, previous studies focused on the outcome of flow redistribution but neglected the process, leading to poor knowledge of deflection flow at intersections. In this study, numerical investigations of the deflection flow in cross fractures were carried out based on Navier-Stokes equations and the results were compared with previous experiments. Geometrical characteristics such as angle(φ), aperture ratio(k), and hydraulic characteristics like inlet flow ratio(n) were considered to explore the mechanism of deflection flow. The deflection flow intensity(Xφ) was introduced to characterize the magnitude and direction of the deflection flow. The results showed that the deflection flow is caused by unequal local head loss. The effect of φ on Xφ is limited by n and k. Increasing n or k enhances the deflection flow but the directions of the induced deflection flow are reversed. The obtained relationship was further supported by theoretical results derived from the cubic law. Subsequently, sensitivity analysis of impact factors to the deflection flow was carried out by the Morris method, the sensitivity in descending order was k, n, φ. Finally, based on the analysis of Xφ, the conditions to limit the occurrence of deflection flow was obtained as a linear positive correlation between the critical inlet flow ratio(nc) and aperture ratio(k). The results from this study may provide insights and physical constraints on construction of flow models based on discrete fracture networks.

Research on the influence of system drainage holes on the head loss of water transmission systems

Abstract To ensure the structural safety of the thin lining structure of the tailwater tunnel, this study used three-dimensional flow field numerical simulation technology to conduct an in-depth analysis of the drainage holes set along the tunnel body, to evaluate the impact of drainage holes on the overall and local head loss of the tunnel under different system layout types. It aims to provide scientific theoretical support and practical reference for engineering design and achieve more efficient and stable tunnel hydraulic operation conditions.

Research on hydraulic characteristics’ sensitivity analysis of the hydraulic inclined shaft turning

Abstract The parameters of the hydraulic inclined shaft turning directly affects the flow field characteristics in the bending section and the construction difficulty of the bending section. Three-dimensional computational fluid dynamics (CFD) numerical simulation method was used to systematically study the hydraulic characteristics under different flow velocities, turning radii and turning angles. The results indicate that the flow velocities and the size of the turning radius have little influence on the flow velocity distribution in the bending section. The larger the turning angle, the larger the fast flow velocity area in the bending section. But the extreme values of fast flow velocity remain basically unchanged, and the length required for adjusting the flow velocity distribution after the curved section becomes longer. The faster the flow velocity, the smaller the turning radius, and the larger the turning angle, the greater the centrifugal force generated and the more pronounced the difference in pressure distribution between the inside and outside of the bend section. The head loss in the bending section is consistent with the empirical formula in the specifications. As the radius of curvature gradually increases from 1D to 3D, the head loss (primarily due to local head loss) decreases gradually. When the radius of the bending section continues to increase, the reduction in local head loss becomes less significant, but the increase in frictional head loss leads to a slight overall increase in head loss.

Local Head Losses And Drag Coefficients Characterization In Coastal Infrastructures

Some coastal infrastructures (i.e. intakes, outfalls, gates) incorporate singular elements (meshes, nets or grids) which, through their interaction with the water flow, can produce large changes in the water level (upstream and downstream) and forces on them. Therefore, an accurate definition of local head losses (to characterize water level changes) and drag coefficient (to characterize drag forces) allows to optimize their designs (configuration and geometric definition).

A study of the flow characteristics with natural accumulations of vegetative floating matter at trash racks

Rivers and reservoirs with rich vegetation resources may suffer from the natural accumulations of vegetative floating matter (VFM) at trash racks. The relationship between hydraulic parameters and physical characteristics of natural VFM accumulations needs to be developed. This research experimentally simulated the natural VFM (leaf-type, fascicled-type, and mixed-type) accumulation at trash racks, varied by flow rate, VFM quantity, and release position. The blockage of cross-section, increase in local head loss, and changes in flow distribution with a natural VFM accumulation were quantified. The results indicate that the hydraulic parameters and physical characteristics of natural VFM accumulations are closely related to the structure of VFM. The head loss and the percentage of gap flow due to the accumulations of leaf type-VFM are numerically lager than that of fascicled-type VFM. Furthermore, the head loss and flow distribution were estimated based on the types of VFM, blockage ratio and the original Froude number. Considering the natural accumulation, a total flow prediction was proposed without estimating the resistance coefficient. This work provided basis for the management and prediction of VFM accumulations in river systems.

Analysis of energy loss in the helical hedge flow channel of fruit tree root emitter

This paper proposes the design of a helical hedge flow channel with a high energy loss, which shows promising potential for application in fruit tree root emitters. The aim is to investigate the relationship between the energy loss form in the channel and its influencing factors. The hydraulic performance testing method is employed to analyze the factors that affect energy loss. The main influencing factors are determined using the response surface methodology (RSM) for experimental design. Based on the obtained experimental results, the energy loss form and influencing factors are analyzed, and a prediction model for the energy loss coefficient (ξ) is established. The results indicate that the ξ exhibits a decreasing trend with an increase in the diversion angle (α), a trend of first increasing and then decreasing with an increase in the channel width (b), and an increasing trend with an increase in the number of channel units (n). The effects of the straight section length (l1), convergence section length (l2), and bend radius (r) on the ξ can be neglected. The ranking of the geometric parameters' influence on the ξ is as follows: n > b > α > l1 > r > l2. The experimental results reveal that the ξ ranges from 19.2 to 234.3. Furthermore, the head loss along the flow channel constitutes merely 0.06–0.47% of the local head loss, The main form of energy loss in the spiral counter flow channel is local head loss. There is a significant linear relationship between α, b, n and the ξ, The established prediction model (R2 = 0.9691) can accurately predict the ξ of the channel.

Experimental investigation on flow of trash rack blockage in front of pumping station

Trash rack blockage significantly affects the water levels and velocity distributions near trash racks, influencing the performance of subsequent hydraulic systems. An experiment was conducted where alligator weeds, green grasses, woven bags, denim, and cotton fabrics were used as typical trash. Under different amounts of trash, approach velocities and water depths, the movement and aggregation characteristics of the trash were observed and measured. The water level difference and the velocity distributions of cross-sections near trash racks were measured and analysed. A general dimensionless expression was advanced to calculate the head loss coefficient of the trash rack. We introduced the local head loss formula of trash rack blockage based on measured velocity distributions. The results indicate that the water level difference is related to blocked trash characteristics and the approach velocity. The velocity distributions are determined by the blocked location and blocked area on the rack surface. Backflow occurs in severe blockage, which makes the velocity distribution uneven and increases the local head loss.

Study on the Head Loss of the Inlet Gradient Section of the Aqueduct

The form of the inlet section of aqueducts that connect the upstream channel and the downstream channel affects the flow pattern and head loss. In order to provide a reference for the design of the gradient section of water-transfer channels, a typical three-dimensional hydrodynamic model is established in this paper based on existing results. The results show that the local head loss coefficient is related to the cross-sectional area of the inlet and outlet of the gradient section, the water surface contraction angle of the gradient section, and the elevation difference between the bottoms of the inlet and outlet of the gradient section, and a functional relationship is provided; when changing the width of the inlet and outlet bottoms, the local head loss coefficient is negatively related to the water surface contraction angle and increases with the increase in Wup/Wdown; the local head loss coefficient has a good exponential function with Wup/Wdown. The research results can provide a reference for the design of the inlet gradient section and the solution of the head loss coefficient.

Thermal balance and gap flow of high-pressure, large-scale plunger pairs

Fitting gaps are a critical factor affecting the efficiency of high-pressure, large-scale plunger pumps. In actual work, fitting gaps change under liquid pressure and temperature rise, and the fluid flow in the annular channel changes under the fitting gap, in turn affecting the fitting gap. Therefore, on the basis of the thermo-fluid–structure interaction, a thermodynamic analysis model of plunger friction pairs is established in this work. The model considers the heat production due to plunger pair friction, frictional head loss, local head loss and heat dissipation caused by the fluid and air. Given that heat production and dissipation are greatly affected by annular channel flow, the deformation and leakage equations of the large-scale annular channel are established on the basis of pressure and temperature rise. In consideration of the gap deformation, gap flow, heat production, and heat dissipation of the plunger, a thermal balance equation is established, and the temperature rise of the plunger pair under different initial gaps is analyzed. In addition, a plunger pump experiment system is built to test the temperature rise of the plunger pair. Results show that the model can effectively predict the temperature of the plunger friction pair. The research results can provide a theoretical basis for the design of large-scale, high-pressure gap seals.

Analysis of local head losses in microirrigation lateral connectors based on machine learning approaches

The presence of emitters along the lateral, as well as of connectors along the manifold, causes additional local head losses other than friction losses. An accurate estimation of local losses is of crucial importance for a correct design of microirrigation systems. This paper presents a procedure to assess local head losses caused by 6 lateral start connectors of 32- and 40-mm nominal diameter each under actual hydraulic working conditions based on artificial neural networks (ANN) and gene expression programming (GEP) modelling approaches. Different input–output combinations and data partitions were assessed to analyse the hydraulic performance of the system and the optimum training strategy of the models, respectively. The range of the head losses in the manifold (hsM) is considerable lower than in the lateral (hsL). hsM increases with the protrusion ratio (s/S). hsL does not decrease for a decreasing s/S. There is a correlation between hsL and the Reynolds number in the lateral (ReL). However, this correlation might also be dependent on the flow conditions in the manifold before the derivation. The value of the head loss component due to the protrusion might be influenced by the flow derivation. DN32 connectors and hsM present more accurate estimates. Crucial input parameters are flow velocity and protrusion ratio. The inclusion of friction head loss as input also improves the estimating accuracy of the models. The range of the indicators is considerably worse for DN40 than for DN32. The models trained with all patterns lead to more accurate estimations in connectors 7 to 12 than the models trained exclusively with DN40 patterns. On the other hand, including DN40 patterns in the training process did not involve any improvement for estimating the head losses of DN32 connectors. ANN were more accurate than GEP in DN32. In DN40 ANN were less accurate than GEP for hsM, but they were more accurate than GEP for hsL, while both presented a similar performance for hscombined. Different equations were obtained using GEP to easily estimate the two components of the local loss. The equation that should be used in practice depends on the availability of inputs.

Flow modelling and energy consumption of a hydrotransportation system possessing variable flow boundaries

The design and choice of pipe fittings in such systems plays an important role as far as headloss and flow separation are factors of concern. This study aims to investigate the flow of coal water suspension through a converging section, diverging section and a bend using computational fluid dynamics approach. The modelling and simulation are carried out on geometries consisting of both converging and diverging sections of variable angles along with a bend of R/d ratio of 2. The computational fluid dynamics simulation results are in good agreement with the experimental data, with an average percentage error of 1.96%. 1° angle of divergence and 7° angle of convergence are optimum designs for the lowest local headloss. However, the headloss across the entire test section is found to be minimum for the case where the angle of convergence/divergence is fixed at 1° each. The specific energy consumption gives a practical idea about the minimum energy required for the transportation of solids through some distance, which is an all-time minimum for the suspension containing 60% solids by mass. The study presents a detailed investigation into the local as well as global flow characteristics of the coal water suspension through a test section.

Application of Head Loss Coefficient for Surcharge Straight Path Manhole to Improve the Accuracy of Urban Inundation Analysis

Currently, adopted runoff analysis models focus on the characteristic factors of watersheds and neglect the analysis of the flow in conduits. Additionally, the usually employed XP-SWMM modeling package generally underestimates the flood area because it considers manholes as nodes and does not consider local head losses according to the shape and size of the nodes. Therefore, it is a necessity to consider the loss coefficient in surcharge manholes to improve inundation and runoff analysis methods. This study aims at improving the accuracy of discharge analysis before analyzing the storage and runoff reduction effects of storage facilities. Hydraulic experiments were conducted according to the changes in discharge and manhole shapes. We show that the flood area increases as the overflow discharge at manhole increases due to the application of the head loss coefficient. We demonstrate a concordance rate ≥95% between results and observed flood area when accurate input data (from the parameters of the target watershed) and the head loss coefficient (from hydraulic experiments) are applied. Therefore, we demonstrate that the result of our 2D inundation analysis, considering the head loss coefficient in surcharge manhole, can be used as basic data for accurately identifying urban flood risk areas.

CFD simulations of hydraulic short-circuits in junctions, application to the Grand’Maison power plant

In the framework of the XFLEX HYDRO H2020 European Project, the pumped-storage power plant of Grand’Maison (France), owned by Electricité De France, focuses on the implementation of the hydraulic short-circuit (HSC) operating mode. This mode increases the flexibility in pumping mode, which helps the integration of intermittent energies. Grand’Maison is divided into two power houses: the first features four Pelton turbine units and the second eight reversible pump-turbines units. A trifurcation splits the flow into three penstocks, each is then split into two branches that feed each power house. The HSC operating mode, which consists in operating the pumps and the Pelton turbines simultaneously, changes the flow paths in the junctions compared to the pump mode. The power plant was not designed to operate in HSC mode over a long duration, therefore an assessment of its feasibility is necessary. 151 computational fluid dynamic simulations are carried out for two bifurcations and one trifurcation. The numerical simulation results show that the local head losses in HSC mode represent less than 1% of the gross head. No flow instabilities are observed at the bifurcations contrary to the trifurcation. Additional analyses are required to better understand the flow in the trifurcation.

Research on the Law of Head Loss of Jet Pumps in the Cavitation State

Liquid flow is subject to head loss because of viscous force, surface tension, friction force, and so on. Part of the energy is irreversibly converted into heat, which then dissipates into the environment. Head loss intensifies in the turbulent state. At present, few studies explore the law of head loss caused by secondary flow, cavitation intensity, and turbulence intensity. In this study, the head losses in different sections of a jet pump were studied by controlling the cavitation number σ, the secondary flow rate Qs, and the inlet pressure pi. The experimental results were analyzed with the aid of computational fluid dynamics. The results show that an increase in Qs can weaken the variations of Qs and suction pressure ps in the transitional stage of cavitation. Besides, σ, Qs, and pi influence head loss to varying extents. Cavitation intensity and turbulence intensity are the main factors for head loss and jet temperature difference. In particular, the influence of Qs on head loss provides guidance both for reducing the energy loss of the quantitative adding device and jet aerator and for expanding the stable adding range of the jet. More importantly, the main factors of energy loss caused by jet cavitation were analyzed in detail, which can effectively facilitate the pipeline design to reduce the local and frictional head loss.

Mathematical model of hydraulic ram pump system

The hydraulic ram pump is water-powered machinery using low-head hydroenergy. An overall mathematical model is presented to consider the dynamic behavior of the waste and delivery valves. Model experiments, numerical simulations, and references analysis are combined to investigate the characteristics of pressure and water level fluctuations, the motion of the waste and delivery valves, as well as corresponding performance optimizations. The mathematical model can well represent the pressure and water level characteristics of the hydraulic ram pump, as well as the motion of the waste and delivery valves. The numerical results are in good agreement with the measured peak value, trough value, waveform, and period. The opening and closing of the waste valve are found to meet the power-function of time with the power exponents 1.5 and 0.2, respectively, while the delivery valve can experience multiple opening-closing processes for low lift cases. The partial water volume in the air chamber flows back into the pump body during the closure of the delivery valve, resulting in the degradation of the delivery flow. The delivery valve of perforated structure is a priority for the high lift case due to reducing backflow, while that of lift-check-valve structure is advised for other cases because of the small local head loss coefficient.

Determination of the Equivalent Length for Evaluating Local Head Losses in Drip Irrigation Laterals

HighlightsA hydraulic model was used to determine the value of the equivalent length for evaluating local emitter head losses in drip laterals.Dimensional analysis was used to develop an equation for predicting the equivalent length.The effects of the design variables on the equivalent length were investigated.The accuracy of the equation was validated by a previous experiment and an alternative hydraulic model.Abstract. The equivalent length is widely used in current hydraulic models to estimate local emitter head losses for the analysis and design of drip irrigation laterals. The accurate evaluation of the equivalent length is therefore required in the lateral design procedure. In this study, a finite element model was used to develop an equation to predict the equivalent length. Eight design variables were selected, and 32 lateral cases were generated using the orthogonal design. The total local head loss in the 32 laterals were firstly calculated using the local head loss coefficient multiplied by the kinetic head. The solutions were considered as exact values and being equivalent to friction head losses, and the equivalent length was computed using the Darcy-Weisbach equation. Dimensional analysis and regression procedures were then used to obtain the prediction equation related to the selected variables. The results show that the converted equivalent lengths accurately estimated the local head losses in the 32 laterals. The local head loss coefficient was the most important factor for the equivalent length, followed by the lateral diameter. The effects of the lateral inlet pressure head, flow exponent, nominal flow rate of emitter, number of emitter, emitter spacing and lateral slope were not significant. Two models were developed to predict the equivalent length, and to calculated the total local head losses. The results demonstrated satisfactory agreement with the measured value available in a previous experimental study, with RMSE = 0.202 and 0.162 m for the full and simplified model, respectively. The percent error between the measured and calculated total head losses using simplified model was from -16.5% to 14.8%, and the Camargo and Sentelhas coefficient c was higher than 0.98. The equations were therefore capable for evaluating the local head loss in the hydraulic design of drip irrigation laterals. Keywords: Dimensional analysis, Finite element method, Hydraulic design, Pressure head, Uniformity.

A Fractal Model for Thermal Dispersion Coefficients of Porous Media

The thermal dispersion coefficient is an important parameter to characterize heat and mass transfer in porous media, which is related to the physical properties of fluid and the structure of porous media. The pore-throat structure model for fractal porous media was established, and the local head loss and the velocity dispersion effect were studied for the fluid changing from the turbulent state to the laminar state around the pore-throat structure. The thermal dispersion coefficient formula was derived under the influences of the micropore-throat structure and the velocity dispersion effect. The results show that, the thermal dispersion coefficient is directly proportional to the pore-throat ratio, the number of pore-throat structures and the tortuous fractal dimension, and is inversely proportional to the porosity and the area fractal dimension. Furthermore, in the range of 1~150, the pore-throat ratio has a significant influence on the velocity dispersion effect, and the fluid has a local head loss around the pore-throat structure, which leads to an enhancement of the velocity dispersion effect and an increase of the thermal dispersion coefficient.

Mechanism research and field test of a novel axial vibratory tool for friction reduction in long horizontal wells

When drilling long horizontal wells, the axial vibration generated by the drilling string at the bottom hole will effectively alleviate the phenomenon of “frictional drag of the drill bit”, which can reduce the friction and enhance the penetration rate. Based on the principle of vibration impact, the axial vibratory tool for friction reduction with a diameter of 127 mm was designed, and the mechanical structure and working principle of this tool were also introduced in detail. First, the planar planetary motion of the throttle valve was described, and a model for calculating the cross-flow area at different moving valve and fixed valve sizes was established. Then, considering the effect of local head loss, the mechanical analysis of the working pressure drop generated by the fluid at each site within the dynamic short connector was carried out, and the relationship curves of the working pressure drop with time and cross-flow area were obtained. After that, the Viscous-Realizable k-ε turbulence model was used to simulate the water hammer pressure of the dynamic short connector, and the variation of water hammer pressure with time, cross-flow area, and cross-sectional flow velocity under 3D/2D conditions was obtained. Based on the undamped vibration differential equation, the axial impact force and axial vibration displacement generated by the vibratory tool were solved. The calculated results are in good agreement with the experimental test results. The field test of this vibratory tool was conducted in well FNHW4084 of the Mahu oil field in Xinjiang, China. The tool was in the well for 10.68 days. The drilling fluid was circulated for 202 h. The pure drilling time was 125.83 h. The drilling footage of a single tool is 596 m with an average penetration rate of 4.74 m/h. Rate of penetration in the test section was increased by 254% compared with the upper section. Compared with the same kick-off section of the neighboring well FNHW4026, the one-trip drilling footage of the test section was increased by 150% and the penetration rate was increased by 126%. The field test results present that this vibratory tool can significantly increase the drilling footage and penetration rate of horizontal kick-off section.

THE HYDRAULICS OF NATURE-LIKE FISHWAYS

Nature-like fishway arrangements are commonly used because these structures imitate the characteristics of natural rivers and effectively allow fish to migrate past river sections blocked by hydraulic structures. In this paper, physical models were analyzed, and the velocity distributions of two different fishway structures (Types I and II) were compared. Results showed that the maximum mainstream velocity of the Type I structure was 5.3% lower than that of the Type II structure. However, the average mainstream velocity of the Type I structure was 21.1% greater than that of the Type II structure. The total per-cycle length of the mainstream path in the Type II structure was 2.1 times greater than that of the Type I structure, which indicated that the length of the mainstream path was somewhat proportional to the average velocity of the mainstream. When the flow rate was kept constant, increases in the velocity of the main flow associated with changes in the internal structure of the fishway decreased the average velocity of the main flow, while decreases in the total length of the flow path led to increases in the average velocity of the main flow. Due to frictional head loss along the fishway and local head loss, as well as the overlaps between these factors, the overall flow rate gradually decreased every cycle, despite periodic fluctuations.

Theoretical and experimental study on the local head loss effect of complex rock fracture networks

Theoretical and experimental study on the local head loss effect of complex rock fracture networks