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Hydropower units undertake the tasks of frequency modulation and peak load regulation, flood control and discharge in flood season. When the unit working condition changes greatly, the stability of unit output will be affected. Therefore, the study of the transient process is of great significance to maintain the stability of hydropower units. This paper introduces a calculation method of transition process based on comprehensive characteristic curve. Based on the data of the comprehensive characteristic curve of Chaijiaxia hydropower station, the full characteristic surface of the turbine is obtained by BP neural network algorithm. Finally, the differential algebraic equation of the transient process of the turbine is established, and the transient process is solved by combining with the full characteristics of the turbine.

With the development of offshore oilfields, foreign companies and research institutes spend plenty of resources on the research of subsea multiphase pump. The helico-axial multiphase pump is generally characterized by large flow and high head unit, and has the advantages of good anti-sand performance, simple structure and small volume. This paper introduces the design of the two-stage compression unit model of a helico-axial multiphase pump by using CFD method. A numerical simulation of full three-dimensional flow field is carried out to study the blade number and the wrap angle influence on external characteristics of the pump. The optimum design combination is selected as the research object and the influence of different inlet gas volume fraction on the internal and external characteristics of the pump is discussed. The design and hydraulic analysis of the multiphase pump can provide a basis for its use in the offshore oil-gas gathering and transportation system.

Hydro-abrasive erosion due to sediment flow often leads to the efficiency loss, seriously vibration, and sometimes even failure for Pelton turbines. This kind of erosion can be greatly intensified when the concentration of sand increases. It is of paramount importance to study the erosion mechanism for such machines, especially in Asia, where the sand concentration in many rivers is relatively higher due to some geologically young mountains like the Himalayas. In this study, the erosion patterns of the injector have been predicted at high sand concentration. The simulated scenario was based on continuous measurement of sediment flow during the flood season in an power plant. Firstly, the three-dimensional modeling for the whole flow domain of the injector with jet has been carried out by ANSYS Fluent. The free air-water flow from the injector has been simulated with the SST k-ω turbulence model, where the VOF (volume of fluid) model was implemented to capture the air-water interface. Then after tracking the particle movement in the air-water flow by the Lagrangian method, the Mansouri model was adopted to predict the erosion patterns. The erosion mechanism was explained by detailed analysis of particle impact properties like the average hits, the impact velocity, and the impact angle. The results show that the “velocity deficit region” will reduce erosion on the needle tip. In addition, abrupt geometry change can be designed at low-velocity regions to reduce erosion. This paper can provide a better understanding of the erosion mechanism, which can help to reduce wear in future designs.

Currently, untapped water resources in China are mostly located in the southwestern region notable for high ranges of Qingha-Tibet Plateau, Hengduan Mountains and Yunnan-Kweichow Plateau. These water resources have the remarkable property of being high in water head within a short distance. The Pelton turbine counts as the most adequate type of water turbine to harness these water resources. An internal-controlled Pelton nozzle design is elucidated in this paper in line with the formula and an existing model in the case of a1100m water head [1]. The impact exerted by nozzle and spear angle on the nozzle hydraulic efficiency under a set of needle strokes was ascertained from the numerical perspective. Elucidated hydraulic performance of different nozzle design was anatomized. An energy criterion was proposed through acquiring the jet efficiency to select the appropriate hydraulic design of Pelton nozzle [2]. The numerical results were indicative of the design with 100°/70° combination of nozzle and spear angle that was superior in overall hydraulic efficiency. For this reason, this design can be referenced in engineering applications.

This paper want to analyse the influence of gravity in the axial turbine. In this paper, the influence of axial turbine on the gravity field of different runner diameter is analyzed at the same head, the same opening degree of the guide vanes and runners and the same unit speed. The turbulent model is SST. And in these calculations I consider the impact of runner gap. According to the simulation, when the Fr exceeds 2.3355, the effect of gravity is negligible. When Fr less than 2.3355, the efficiency, flow rate and power considering the gravity are greater than the case without considering gravity. The lower surface of the runner is prone to cavitation when gravity is considered. With the decrease in the diameter of the runner, the difference in pressure distribution between considering the gravity and without consideration of gravity is reduced.

Since the clearance between the runner shroud and the hub can change with the angle of the blades, it has a great influence on the hydraulic characteristics and cavitation performance in the Kaplan Turbine. In this paper, the CFD will be used to solve the turbulence model based on the k-ωSST model in the entire flow field of the turbine and the Zwart-Gerber-Belamri model will be used to predict the cavitation. We compare the hydraulic characteristics and cavitation performance of the Kaplan Turbine under the conditions of the runner clearance exist or the runner clearance absence. Finally, we analysis the influence of the clearance width in the hydraulic performance and the relationship between the clearances and the turbine characteristics.

The hydraulic performance of Pelton turbine is different from reaction turbines due to its unsteady flow of rotating buckets with time and space. The water sheet flow in Pelton turbine is also very complex as the jet flow is often interacted with air and itself. This paper numerically investigates the dynamic hydraulic performance of a Pelton under super-high head. Unsteady numerical simulations were performed using SST k-ω. Two-phase homogeneous model and VOF were adopted to model he free surface flow. The evolution history of water sheet flow in the buckets were presented. The distribution of pressure coefficient on the bucket surface were also analysed. The results indicate that the development of water sheet flow on the bucket surface can be divided into three stages, corresponding to the output power variation process. This calculation can be used to illustrate the hydraulic mechanism of water sheet flow evolution.

Based on the SST liquid turbulence model, using the Euler-Lagrange method to simulate solid-liquid two-phase flow in the centrifugal pump with different degree of wear blades. When the pump was transporting silt-laden flow, numerical simulations with the Euler-Lagrange method to analyse the trajectory of the sands and the mechanism of wear. According to the simulation results, when the flow rate is less than the design flow, the efficiency decreases gradually with the increase of the wear of the runner blade. When the flow rate is larger than the designed flow rate, the efficiency will decrease first and then increase. As the degree of wear increases, the head and power are increasing. With the increase of flow rate, the volume fraction of sand grains distributed in the pressure face of the blades increases, and the distribution of sand grains in the volute outlet change from the uniform distribution of small flow rates to the concentrated distribution of the volcanic surface at large flow rates.

Cavitation is one of the most important and common issues in hydraulic machines. Much attention has been paid on cavitation flow prediction, however, most of the current researches ignore the thermal effects during the cavitation process and have not taken into account the thermodynamic variation of phase change. In the presented paper, the cavitation flow characteristics around a hydrofoil NACA0015 was analyzed by numerical simulations and the results were compared with the experimental data from a reference paper. The focus was put on the cavitation process with respect to thermal effects. Steady and unsteady simulations were performed by ANSYS CFX 16.0 with a modified SST k-ω turbulence model under three different temperature conditions (25°C, 50°C, 70°C). The energy conservation equation was considered to describe the temperature field around the hydrofoil. To ensure the accuracy of simulations, the source term of thermal effects in vapor bubble transformation process was added into the evaporation and condensation functions of cavitation. The results indicated that simulations based on thermodynamic effects could detect the cavitation characteristics in detail and agree well with the experimental results.

A proportional regulating valve is a hydraulic control valve that allows the output of the output oil parameter (pressure) to vary proportionally to the input electrical signal parameter (current or voltage). Due to the non-linearity of the regulating valve system and the problem of poor response characteristics, this paper studies the performance optimization problem of the system. In order to make the system work steadily, by adding iterative learning controller of Proportion-Integral-Derivative type, the system hydraulic pressure increases with the number of iterations gradually approaching the actual pressure required by the load. The simulation results show that the digital regulating valve based on Proportion-IntegralDerivative control law iterative learning control has fast response speed, high control precision and stable operation. So it can be used as an effective solution to achieve high-performance digital regulating valve.

Pelton turbine is widely used in in utilizing the high water head resource. The multiphase flow in the Pelton turbine is too complex to be analysed detailed as the flow in the reaction turbines. So the hydraulic design of Pelton turbine was mainly based on the know-how. The homologous turbine model was the only way to verify its performance in the past. Although an efficiency scale-up equation for Pelton turbines had established in the IEC 60193 code, researches had shown different internal flow phenomena would influence the efficiency scale effects and lead to different efficiency scale for different turbine design. This paper simulates the internal flow of model and homologous prototype Pelton turbine at three relative needle strokes. Homogenous model and SST k-? model will be adopted to simulate the unsteady two-phase flow in the rotating buckets. Unsteady simulation results would help to numerical investigate the scale effect of Pelton turbine.

For the low-head hydropower station, the operating head is low, and the turbine intake channel is relatively short. The turbine internal flow behaviour can be influenced by fluid flows in the upstream reservoir easily, then it would influence the turbine hydraulic performance. Water flows in the upstream reservoir can be influenced by the Coriolis force by the Earth rotation, and it differs at the different Rossby number. In this paper, the Coriolis effect on the approach flows and the turbine performances are investigated numerically for the low-head units. Firstly, the Coriolis effect (under the different latitudes and the same characteristic length scale) on reservoir flows was predicted. Secondly, the prototype performance of a bulb-type turbine was simulated including the reservoir flow with the Coriolis effect, and then the effect on the turbine performance is be discussed. Results show that the flow field in the upstream reservoir at the low Rossby number, the ratio of inertial force to Coriolis force, can sufficiently influence the turbine intake flows and the turbine performances. Adjusting the side-wall distance can reduce the Coriolis effects.

The internal flow in the rotating bucket of Pelton turbine is free water sheet flow with moving boundary. The runner operates under atmospheric and the cavitation in the bucket is still a controversial problem. While more and more field practice proved that there exists cavitation in the Pelton turbine bucket and the cavitation erosion may occur at the worst which will damage the bucket. So a well prediction about the cavitation flow on the bucket surface of Pelton turbine and the followed cavitation erosion characteristic can effectively guide the optimization of Pelton runner bucket and the stable operation of unit. This paper will investigate the appropriate numerical model and method for the unsteady 3D water-air-vapour multiphase cavitation flow which may occur on the Pelton bucket surface. The computational domain will include the nozzle pipe flow, semi-free surface jet and runner domain. Via comparing the numerical results of different turbulence, cavity and multiphase models, this paper will determine the suitable numerical model and method for the simulation of cavitation on the Pelton bucket surface. In order to investigate the conditions corresponding to the cavitation phenomena on the bucket surface, this paper will adopt the suitable model to simulate the various operational conditions of different water head and needle travel. Then, the characteristics of cavitation flow the development process of cavitation will be analysed in in great detail.

At present it is possible to predict more accurately by various numerical methods established for cavitation simulation around a hydrofoil. However, for the solution of the complex unsteady cavity flow, it is still marginal. In this paper, numerical method is adopted to simulate cavitation around 3-D NACA0015 hydrofoil with homogeneous two-phase flow calculation using commercial code CFX-solver with two turbulence models, the standard RNG k- turbulence model and the modified RNG k- turbulence model respectively. First, pressure coefficient for non-cavitating flow, time averaged values of unsteady cavity flow around a hydrofoil are verified to simulate more closely to an actual cavity flow. And then frequency analysis is performed with Fast Fourier Transform. The results show that the calculation results with modified RNG k- turbulence model agree with experimental results in terms of mean cavity length and pressure drop, but the unsteady flow characteristics of oscillating cavitation still deviate slightly in terms of unsteady cavity flow.

Cavitation is one of the key issues affecting the safe and stable operation of centrifugal pumps. This research conducted numerical simulations of the 3-D turbulent flow in the whole flow passage of a centrifugal pump using RANS method. The calculation results of cavitation characteristics agreed well with the experimental results, which were based on SST k-ω turbulence model and Zwart-Gerber-Belamri cavitation model. This paper analysed the cavitation development process and the corresponding pump performance for three typical conditions, namely large discharge condition, design discharge condition and small discharge condition, by changing the available Net Positive Suction Head (NPSHa). For large discharge condition, the incipient NPSHa was large, while for design discharge condition and small discharge condition, the incipient NPSHa values were almost the same and both small. As the flow rate decreased, the critical NPSHa decreased as well, and the cavitation positons gradually shift from the pressure surfaces of some blades to the suction surfaces. At the same time, the tongue has greater effect with larger flow rate and the cavitation becomes less unsteady with the decrease of flow rate. With similar vapour volume, cavitation on the blade pressure side more easily leads to the drop of pump performance. Therefore, more attention should be paid to the cavitation characteristics of centrifugal pumps in large flow conditions in hydraulic design stage.

The operational stability of the pump turbine at the pump mode will be greatly influenced by large pressure fluctuations when operated in the small-discharge conditions. Therefore, it is significant to analyse the flow characteristic under the small discharge operating conditions deeply. Study of the internal flow in the small discharge condition has been investigate in great detail combined with model experiments in this paper. The SST k-ω turbulence model is adopted to perform three-dimensional numerical simulation of the entire pump-turbine flow passage at optimal guide vanes opening. The numerical simulation results match well with experimental data. Then internal flow under the small discharge condition is analysed. The results show that the dominant frequency inside the flow passage is a relative low frequency. In addition, there are obvious complex flow phenomena inside the draft tube, runner and diffuser domains, such as secondary flow, backflow and even vortex, leading to strong unsteady flow and significant pressure fluctuation.

Stock pumps cost 25 percent of total power consumption in a modern paper mill. Owing to the severe erosion of pump casing and impeller during operation, stock pump often results in efficiency drop and rising power consumption. A favourable prediction of the impeller wearing character can effective guide optimization design of stock pump impeller. Thereby it can reduce impeller wear and extend stock pump performance life. We simulated the three-dimensional unsteady solid-liquid two-phase flow characteristic in the hydraulic channel of a low specific speed stock pump with open and three blades impeller. The standard k- e turbulent model and the pseudo-fluid model were adopted in simulation. Clearance between covers and impeller is taken into consideration in modelling, and pulp is simplified into mixtures of solid particles and water. The Finnie prediction model is applied to predict impeller erosion character. The simulation results of different solid particle size are compared with practical impeller erosion character, and the effects of solid particle size on impeller erosion character are obtained. Thus, numerical method to simulate impeller erosion characteristics of fibered pulp is investigated.

With the technology of Computational Fluid Dynamics (CFD), this paper conducts a 3D numerical simulation for the oil and gas flow field in the Pump turbine guide bearing rotating sump. VOF model is adopted in this simulation. This study calculates distribution of the oil-air phase and characteristics of the pressure. The influence of sump rotating speed, oil level and oil viscosity on the pressure at the inlet of oil-immersion plate are discussed. The results demonstrate that the static pressure at the inlet is roughly proportional to oil level. Too low level may result in the separation between lubrication oil and supply hole on the oil-immersion plate, which then disables the oil supply. The static pressure at the inlet increases parabola as the sump rotating speed increases. To ensure the supply pressure, the unit is not suitable for long time operation under low rotating speed. The temperature-viscosity effect of the lubricant oil has little influence on the oil pressure at the supply hole. This paper provides a theoretical base for the safe design and operation of the pump turbine rotating sump, and offers the inlet boundary condition for the analysis of the oil film dynamic characteristics of the turbine guide bearing.

As a renewable energy, marine currents get more and more attention. Thus the development of marine current turbines is critical to the use of this energy. We use large-eddy simulation to analyse the flow field characteristics by full geometry of a horizontal axis marine current turbine. Under the effect of a discrete number of blades, blade tip vortices develop and produce velocity variation near rotor. Referring to the flow induction factors in BEM theory, this paper focuses on the study of axial and tangential velocity and it is found that the main induced velocity component by the vortices is axial velocity. According to the distribution of the two velocity components along circumferential orientation, three peak-valley values corresponding to the number of blades reflect the flow non-uniformity due to the effect of a discrete number of blades even for the upstream of rotor. Meanwhile, this effect will continue developing due to the analysis of flow characteristics in the downstream field.

Nowadays tidal current energy is considered to be one of the most promising alternative green energy resources and tidal current turbines are used for power generation. Prediction of the open water performance around tidal turbines is important for the reason that it can give some advice on installation and array of tidal current turbines. This paper presents numerical computations of tidal current turbines by using a numerical model which is constructed to simulate an isolated turbine. This paper aims at studying the installation of marine current turbine of which the hydro-environmental impacts influence by means of numerical simulation. Such impacts include free-stream velocity magnitude, seabed and inflow direction of velocity. The results of the open water performance prediction show that the power output and efficiency of marine current turbine varies from different marine environments. The velocity distribution should be clearly and the suitable unit installation depth and direction be clearly chosen, which can ensure the most effective strategy for energy capture before installing the marine current turbine. The findings of this paper are expected to be beneficial in developing tidal current turbines and array in the future.

The internal flow of a Pelton turbine is quite complex. It is difficult to analyse the unsteady free water sheet flow in the rotating bucket owing to the lack of a sound theory. Affected by manufacturing technique and silt abrasion during the operation, the bucket surface roughness of Pelton turbine may be too great, and thereby influence unit performance. To investigate the effect of bucket roughness on Pelton turbine performance, this paper presents the numerical simulation of the interaction between the jet and the bucket in a Pelton turbine. The unsteady three-dimensional numerical simulations were performed with CFX code by using the SST turbulence model coupling the two-phase flow volume of fluid method. Different magnitude orders of bucket surface roughness were analysed and compared. Unsteady numerical results of the free water sheet flow patterns on bucket surface, torque and unit performance for each bucket surface roughness were generated. The total pressure distribution on bucket surface is used to show the free water sheet flow pattern on bucket surface. By comparing the variation of water sheet flow patterns on bucket surface with different roughness, this paper qualitatively analyses how the bucket surface roughness magnitude influences the impeding effect on free water sheet flow. Comparison of the torque variation of different bucket surface roughness highlighted the effect of the bucket surface roughness on the Pelton turbine output capacity. To further investigate the effect of bucket surface roughness on Pelton turbine performance, the relation between the relative efficiency loss rate and bucket surface roughness magnitude is quantitatively analysed. The result can be used to predict and evaluate the Pelton turbine performance.

Using tidal energy can reduce environment pollution, save conventional energy and improve energy structure, hence it presents great advantage and is developing potential. Influenced by flood tide and low tide, a fully functional tidal power station needs to experience six operating modes, including bidirectional generation, pumping and sluice; the internal unsteady flow pattern and dynamic characters are very complicated. Based on a bidirectional tidal generator unit, three-dimensional unsteady flows in the flow path were calculated for four typical operating conditions with the pressure pulsation characteristics analyzed. According to the numerical results, the internal flow characteristics in the flow path were discussed. The influence of gravity to the hydraulic performance and flow characteristics were analysed. The results provide a theoretical analysis method of the hydraulic optimization design of the same type unit as well as a direction for stable operation and optimal scheduling of existing tidal power unit.

Different from the reaction turbines, the hydraulic performance of the Pelton turbine is dynamic due to the unsteady free surface flow in the rotating buckets in time and space. This paper aims to present the results of investigations conducted on the free surface flow in a Pelton turbine rotating buckets. The unsteady numerical simulations were performed with the CFX code by using the Realizable k-e turbulence model coupling the two-phase flow volume of fluid method. The unsteady free surface flow patterns and torque varying with the bucket rotating were analysed. The predicted relative performance at five operating conditions was compared with the field test results. The study was also conducted the interactions between the bucket rear and the water jet.

The unsteady flow within the entire flow passage of a pump-turbine with misaligned guide vanes (MGV) device under the rated speed was simulated using the Reynolds-averaged Navier-Stokes equations together with the k-ω based SST turbulence model. Three kinds of MGV arrangement of different opening angles were chosen to analyse the influence of MGV on the pressure pulsation in the flow passages of spiral case, stay vanes, guide vanes, rotating runner blades and draft tube. The characteristics of the dominant frequency of the unsteady flows in different flow parts under different misaligned guide vane arrangement/openings and the hydraulic performance of the pump-turbine were investigated at the turbine operating condition. The computation result shows that the MGV can decrease the peak-to-peak amplitude of the pressure fluctuation in the whole flow passage except the rotating runner blades. The low frequencies and the influence of Rotor Stator Interaction (RSI) in the entire flow passage vary with the arrangement/ openings of MGV.