High Water Head Research Articles

Hydraulic analysis of parabolic flume for flow measurement

Parabolic flumes were designed in the 1994 [7] as an efficient way to provide accurate flow measurement in U-shaped channels. Three-dimensional flow fields in parabolic flumes, long-throated flumes, and Parshall flumes are simulated using the volume-of-fluid model. The hydraulic model was validated by using data of physical model testing. The velocity and turbulent kinetic energy dissipation rate in typical sections of the three measuring flumes are analyzed and the total head curves of the three flumes are obtained. The results indicate that the Parshall flume installed in a U-shaped channel leads to a high water head loss, whereas the water head loss for the parabolic flume is only 35% of that of the long-throated flume or 30% of the Parshall flume, which makes parabolic flumes more suitable for U-shaped channels. A formula for calculating discharge that is applicable to channels of various slopes is theoretically derived. Parabolic flumes are demonstrated to be accurate enough to satisfy the demands of water discharge measurement.

Pelton turbine Needle erosion prediction based on 3D three- phase flow simulation

Pelton turbine, which applied to the high water head and small flow rate, is widely used in the mountainous area. During the operation period the sediment contained in the water does not only induce the abrasion of the buckets, but also leads to the erosion at the nozzle which may damage the needle structure. The nozzle and needle structure are mainly used to form high quality cylindrical jet and increase the efficiency of energy exchange in the runner to the most. Thus the needle erosion will lead to the deformation of jet, and then may cause the efficiency loss and cavitation. The favourable prediction of abrasion characteristic of needle can effectively guide the optimization design and maintenance of needle structure. This paper simulated the unsteady three-dimensional multi-phase flow in the nozzle and injected jet flow. As the jet containing water and sediment is injected into the free atmosphere air with high velocity, the VOF model was adopted to predict the water and air flow. The sediment is simplified into round solid particle and the discrete particle model (DPM) was employed to predict the needle abrasion characteristic. The sand particle tracks were analyzed to interpret the mechanism of sand erosion on the needle surface. And the numerical result of needle abrasion was obtained and compared with the abrasion field observation. The similarity of abrasion pattern between the numerical results and field observation illustrated the validity of the 3D multi-phase flow simulation method.

Numerical Simulation of Fluid-Structure Interaction with Water Hammer in a Vertical Penstock Subjected to High Water Head

The theoretical model of weakly compressible coupling water hammer was established and a FSI program code was developed for coupled weakly compressible water with penstock movement. It combines the weakly compressible water source CFD code and FEM shell element code. The shell element based on orthogonal curvilinear coordinates was completed in FEAP. Meanwhile, the turbulence model in OpenFoam class library was called by using object-oriented technology. This code takes into account both the weak compressibility of water and fluid turbulence characteristics. Using this code, a fluid structure interaction analysis with water hammer was completed. The numerical results agree well with the field test results.

Analysis on Seepage Field and Seepage Control Measure around Kunlong Hydropower Project

The Kunlong Hydropower has high water head and complex geologic environment. It is necessary to study the seepage field and the seepage control measure. In order to set up a three dimensional seepage numerical model around the dam site, double fracture seepage systems contained main fractures network and fractured rock masses is adopted. Pipe to represent a drain hole and fissure to represent a line of holes methods are used in simulation of drainage curtain. After setting boundary conditions and calculating parameter appropriately, the whole seepage field around the Kunlong Dam is calculated with the finite element method. The optimal depths of the impervious curtain and drainage curtain are determined by sensitive analysis. The implications of the analysis results on the design of the project are significant.

Effects of Weakly Compressibility on Propagating Properties of Water Hammer in a Long Pipe

This paper is concerned with propagating features of pressure waves induced by water hammer in a long liquid-conveyed pipe subjected to hyper high water head. Effects of dynamically weak compressibility of the water in pipe and pipe wall elasticity on the propagating physics were investigated by comparing in-site measurements and theoretical analyses. The pressure wave form and propagating speed were significantly effected due to weak compressibility of the water and the interactions of the waves. The wave performs a strong unsteadiness while it propagates along the pipe. This study tries to explain an event with consideration of both the dynamically weak compressibility of the water in pipe and the closing features of the valves controlled actively.

Effects of Weakly Compressibility on Propagating Properties of Water Hammer in a Long Pipe

This paper is concerned with propagating features of pressure waves induced by water hammer in a long liquid-conveyed pipe subjected to hyper high water head. Effects of dynamically weak compressibility of the water in pipe and pipe wall elasticity on the propagating physics were investigated by comparing in-site measurements and theoretical analyses. The pressure wave form and propagating speed were significantly effected due to weak compressibility of the water and the interactions of the waves. The wave performs a strong unsteadiness while it propagates along the pipe. This study tries to explain an event with consideration of both the dynamically weak compressibility of the water in pipe and the closing features of the valves controlled actively.

Wicket Gate Closure Control Law to Improve the Transient of a Water Turbine

The increase in speed and system hydraulic pressure may cause major accidents during the transient of load rejection, especially in high-water head hydropower plants. The current study presents a wicket gate step-by-step closure control law, where two guide vanes will be closed asynchronously to reduce the increase in pressure and improve the transient quality of a waterturbine. Compared with the calculated data in the routine closure law, the control law obviously improved the dynamic qualities of the transient in load rejection and decreased the rising hydraulic pressure from the water diversion system of the plant. The proposed control law can replace the role of a surge tank under certain conditions.

First Infilling of the Venda Nova II Unlined High-Pressure Tunnel: Observed Behaviour and Numerical Modelling

The underground structures of the Venda Nova II reversible hydroelectric power scheme present features that make it an interesting case study. Worthy of mention are the inclination and length of the unlined pressure tunnel, the high water head and the great depth of the powerhouse cavern. In projects of this type, the main effect of the internal water pressure in the pressure tunnel is the establishment of seepage from the tunnel into the rock mass, which can reach the adits and the powerhouse cavern. This seepage is influenced by several factors, such as the geometry of the underground openings, the rock mass properties—namely, the joints characteristics—and the stress state resulting from the excavation and from the internal water pressure. This article presents the main features of the underground structures of the Venda Nova II scheme and a detailed description of the observed behaviour during the first infilling of the pressure tunnel. A three-dimensional multi-laminated numerical model of the rock mass hydromechanical behaviour was developed to help understand the observed behaviour. The model assumptions in regard to the geometry of the openings, the jointing pattern, the rock mass hydraulic and mechanical behaviour, as well as the hydromechanical interaction, are described. Results obtained with the numerical model are presented and compared with the observed behaviour. Finally, the validity and importance of the numerical tools for the interpretation of the rock mass hydromechanical behaviour is discussed.

Selection of Groundwater Control Scheme for Deep Excavation in Alluvial Soil along the Yellow River

Kaifeng locates on a flat and open alluvial plain of the middle and lower reaches of the Yellow River. Owing to its complex history and long-term deposition, a silty stratum with multi-miscellaneous fill and alluvial soil interphase is gradually formed. Combing with the soil actual characteristics of Kaifeng area, which is mainly composed of “high water content”, “high water head”, “strong permeability”, “low strength”, “adequate water supply”, a optimal groundwater control scheme for deep excavation under above complicated geological conditions is proposed. Moreover, the most appropriate waterproof curtain form is recommended for the foundation pit engineering whose excavation depth is less than 10m. The findings of this investigation may offer some suggestions for the choice of groundwater control scheme for construction purpose in similar strata.

The experimental study on inner shift lining structure of freezing shaft in deep thick aquiferous soft rock

In recent years, with the implementation of China’s Great Western Development Strategy, the western coal resource is developing massively. The shafts have wide diameter, the cretaceous formation and the jurassic formation diagenesis later, lower strength, the pore type of aquifer thickness, water, buried deeper and high water head compared to construction of new wells in mid-eastern China. Because of strata is dominated by porous aquifer, bad grouting, serious risks to using grouting system, and the freezing shaft sinking has reliable water tight effect and mature construction techniques, it has been extended and applied. On the structure design of deep freezing side-wall, the related parameters in our country existing design of specifications and manuals that people get from those freezing shaft wall force-mechanism and measure data of the deep alluvium in mid-eastern China, due to the differences in strata’s freezing characteristics and hydrological conditions, it is lacks pertinence on design for shift lining structure of freezing shaft in western deep thick aquiferous soft rock. So we must be further study on frozen shaft lining structure in deep bedrock, find out the mechanical mechanism, design the structure of side-wall properly. For this reason, this article showed the experimental study on inner shaft lining structure of freezing shaft in water-bearing soft rock.

Effect of highly pervious geological features on ground-water flow into a tunnel

Current practice for estimating water inflow rate relies mostly on analytical solutions which assume a homogeneous, isotropic porous medium around a tunnel. Field measurements indicate that current engineering practice does not consistently make adequate estimate of ground-water flow into a tunnel during excavation due to various factors that analytical solutions do not properly take into account. Among the various factors affecting ground-water flow, the significance of a highly pervious feature located near the tunnel is discussed in this research. The highly pervious feature, which is located near an underground opening and connected to a large source of water, can provide a path for relatively high-head water to the joints intersecting the opening. This paper describes the influence of a highly pervious feature on the ground-water flow regime around a tunnel and the change of inflow rate as the tunnel approaches a highly pervious feature.

Discharge Coefficient for a Water Flow through a Bottom Orifice of a Conical Hopper

Discharge coefficients for water flow through a vertical, circular orifice at the bottom of a conical hopper were experimentally studied in the present paper. The conical hopper consists of a cylindrical hopper of inside diameter of 48 cm and a bottom cone of side slope of 45°. Experiments were carried out under different orifice diameters and water heads. The dependence of the discharge coefficient on the orifice diameter and water head was analyzed, and then an empirical relation was developed by using a dimensional analysis and a regression analysis. The results show that the larger orifice diameter or higher water head have a smaller discharge coefficient and the orifice diameter plays more significant influence on the discharge coefficient than the water head does. The discharge coefficient of water flow through a bottom orifice is larger than that through a sidewall orifice under the similar conditions of the water head, orifice diameter, and hopper size.

An efficiency assessment analysis of a modified gravitational Pelton-wheel turbine

A Pelton-wheel impulse turbine is a hydro mechanical energy conversion device which converts gravitational energy of elevated water into mechanical work. This mechanical work is converted into electrical energy by means of running an electrical generator. The kinetic energy of the Water-jet is directed tangentially at the buckets of a Pelton-wheel. The Water-jet strikes on each bucket’s convex profile splitter and get split into two halves. Each half is turned backwards, almost through 180° relative to the bucket on a horizontal plane. Practically this angle may vary between 165° to 170°. Normally all the jet energy is used in propelling the rim of the bucket wheel. Invariably some jet water misses the bucket and passes onto the tail race without doing any useful work. This hydro device is a good source of hydro-electrical energy conversion for a high water head. The present work in this research paper deals with some advanced modifications in the conventional Pelton-wheel so that it can be used for low-head and heavy-discharge applications. Both kinetic and potential energy of the water source is consumed by the runner wheel. Considerable gravitational effect of the water jet is exploited by means of some modifications in a conventional Pelton-wheel. A comparatively heavy generator can be run by this modified Pelton-wheel turbine under low-head and heavy-discharge conditions. The modified features provide enough promising opportunities to use this turbine for Mini and Micro hydro power plants.

Hydraulic characteristics of bottom underlay-type pier for water-wing control

The pier, placed at the outlet of the pressure flow section, is an effective design to deal with the problems of the manufacture and operation of the gates for a discharge tunnel with high water head. It is crucial to control the water-wing, induced by this type of the pier. Through observing the phenomena of the water-wing, the reason of the water-wing inception, i.e., the concave of the flow surface, was presented, and a type of the new pier with bottom underlay was designed. The hydraulic characteristics of the pier, including the variations of the water-wing features, both length and height, with the water head, as well as with the concave depth, and with the height of the bottom underlay, and the variations of the concave depth with the height of the bottom underlay, were investigated by physical model experiments. The results show that the approach of the modification of the concave through the structures with the bottom underlay-type pier is remarkably effective in the water-wing control.

Basic Modeling and Simulation Tool for Analysis of Hydraulic Transients in Hydroelectric Power Plants

In this paper, the simulation system of a typical hydroelectric power plant was developed in a MATLAB/Simulink-based software environment, which has a high water head and a long penstock with upstream and downstream surge tanks and is equipped with a Francis turbine. With MATLAB/Simulink, the models of the proposed simulation system are all modularized and visualized, and can be reused easily. No complex codes have been programmed and the proposed simulation system adapts varieties of hydroelectric power plants. The nonlinear characteristics of hydraulic turbine and then inelastic water hammer effect were considered to calculate and simulate hydraulic transients. Moreover, the influences of different parameters, such as hydraulic turbine speed governor proportional-integral-derivative (PID) gains, pressure water supply system, as well as surge tanks, were analyzed for the dynamic performance of hydraulic turbine regulating system. The digital simulations of a sudden full load rejection for an actual hydroelectric power plant in China were performed, and the results indicate that the proposed MATLAB/Simulink-based hydroelectric power plant simulation system is accurate and effective enough to represent and simulate hydroelectric power plant's nonlinear dynamics as well as to design hydraulic turbine speed control system. The proposed simulation system has also been proved to be useful for preliminary designs or assessments of hydropower projects.

Modelling and control of oscillating-body wave energy converters with hydraulic power take-off and gas accumulator

Oscillating bodies constitute a major class of wave energy converters, especially for offshore deployment. In general, such converters use as power take-off system either a hydraulic system (high-head water turbine or high-pressure-oil hydraulic motor) or a directly driven linear electric generator. The paper addresses the former case, especially when a gas accumulator is employed as energy storage device that provides a smoothing effect to the electric power output. Although there are several wave energy projects currently at different stages of development (including prototype testing) that fit this description, the paper is intended to be a general modelling study rather than to concentrate on a particular device. Special attention is devoted to power take-off performance and design, and to the control of the system.

Analysis of coupled seepage and stress fields in rock mass around the Xiaowan arch dam

AbstractThe Xiaowan arch dam, with a maximum height of 292 m, is located across the Lancangjiang River in Yunnan Province of China, and once completed will be the highest arch dam in China. Because of the high water head and the arch action, it is necessary to analyse the interaction between seepage and stress fields in rock mass around the Xiaowan arch dam. Numerical solution of coupled seepage and stress fields in rock mass around the Xiaowan arch dam is analysed by means of the multi‐level fracture network model and the finite element method. It can be shown from the computation results that storage of the reservoir makes the seepage field change much, and makes the effective vertical stress in rock foundation near the dam and the tensile stress in the abutment rock mass increase, and that the coupled action between seepage and stress fields should be taken into account. Copyright © 2004 John Wiley & Sons, Ltd.

A high-head flat counterbalanced gate

1. In order to increase the capacity of high-head water intakes substantially, it is necessary to develop basically new designs for the gates, providing not only for a decrease in frictional forces in the bearing-guide sections, and, in tum, a reduction in the lifting capacity of the mechanisms, but also a reduction in the loads on the bearing-guide sections. 2. The gate design provides for uniform transfer of the heavy loads received by the gate (of the order of 15,000 tons) onto a large concrete surface. Hydraulic hoists, which have been perfected by industry, are available for maneuvering the gates. 3. Owing to use of a moving structure that operates as a beam on two supports with cantilevers, similar types of gates can be used to close water intakes with even significantly larger cross sections than those designed for the Rogun hydroelectric plant. 4. Model studies of the operation of back-pressure chambers indicated that reliable gate counterbalance is provided for even with complete failure of the chamber seals. 5. As studies indicated, bearing-plate deflectors attached to the basic gate protect the supporting bulkheads under no-head conditions in the outlet section: a flow coursing from beneath the gate has no effect on the lateral surfaces of the bulkheads. 6. The gate is constructed from common grades of steel used at the present time and can be completely fabricated at the plants operated by the Gidromontazh Trust. The gate has no heavy inserted parts fabricated from high-alloy steels. 7. Data from studies conducted on the flat counterbalanced gate and gate chamber indicate that this gate can be applied to deep water intakes at high-head hydrofacilities.

Cavitation resistance of concrete used in hydraulic engineering

1. Cavitation resistance of concretes is closely related to their compressive strengths; the cavitation resistance falls as the strength becomes less, but increase of the strength beyond 500 kg/cm2 produces little increase in cavitation resistance. For linings of conduits, concrete should be used with compressive strength of 450–500 kg/cm2. 2. The parameters of the concrete influence its cavitation resistance in such measure as they improve its strength. For concretes with high cavitation resistance, we would recommend the use of Portland cements with activities of 500–600 kg/cm2, with strong, dense fillers. 3. The method of consolidation and setting has a marked effect on the cavitation resistance of concrete. Hence in concreting the linings of water conduits we must take special measures to get a high-quality surface layer of concrete. 4. Polymer materials are promising for use as linings of outflow channels in high-head water power plants.

Coefficient of Discharge of Freeing Port

It is needful in design of the freeing ports to know discharge coefficients of them. Results of experimental studies now conducted are as follows.1. The fundamental coefficients for full-sized ports (Fig. 1), standing and upright, are shown in Figs. 2-5.2. The coefficient, when ports, small-sized, are standing and upright, is approximately independent of arrangement of deck houses.3. If ports roll, the coefficient will be somewhat decreased at a high water-head and moderately increased at a low head, so long as the ports are situated on the both sides of a well. Of ports along side passages, this tendency will be feeble.4. Orbital motion of a ship does not affect so much to the coefficient.5. We can use in some allowance the coefficient for an uprightly standing port.6. Continuous ports on the both sides of a well, found on cargo ships etc., will discharge water between the top of the bulwark and the upper edge of the port within one period of rolling. A port along a side passage will show the same capacity, if it has an area required by the “Free-board Rule”.7. Deducing the size of port, the coefficient get larger.8. A slant port (Fig. 20), bored in an inclined plane inside a bulwark lest the port-door may open and patter with ship's rolling or by wind, proves some increment even in discharge.