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The irreversible energy loss due to viscous and turbulent dissipation in a Francis turbine led to a decrease in efficiency. It is difficult to reveal the detailed energy loss distribution by either experimental method or traditional simulation method. In this investigation, the entropy production method is applied to calculate the irreversible energy loss quantitatively and demonstrate the spatial distribution of energy loss intuitively. The flow in the Francis turbine is numerically simulated based on SST turbulence model and Zwart cavitation model. The objectives of this study are to (1) verify the accuracy of entropy production method in irreversible energy loss calculation, (2) investigate the detailed characteristics of entropy production rate in blade channel, blade surface and draft tube, (3) reveal the internal interaction mechanism between cavitation process and entropy production rate generation. The results show that the entropy production method has a credible accuracy for irreversible energy loss calculation. Draft tube and runner have the maximum amount of energy loss, but the guide vanes and runner have the maximum ability of irreversible energy loss generation. Finally, the new definition of entropy production rate induced by cavitation is derived to reveal the interaction mechanism between cavitation process and entropy production rate.

With the advantages of large flow capacity, low head, and high efficiency, the tubular turbine can well meet the demand for renewable resources. To obtain its synthetic characteristics in full operating conditions, model tests on both the steady state and transient process were designed and conducted in an ultra-low head bulb turbine. The similitude criteria, model test system, and test method were introduced; experiments on comprehensive steady-state and load-rejection conditions were performed; and the results were analyzed. Based on the steady-state test, the variation of flow, torque, and axial force with respect to the rotating speed, runner blade (RB) opening, and guide vane (GV) opening were revealed. Dynamic test results showed that the closing laws of GV and RB have an obvious influence on the quality of the transient process. Orthogonal optimization was used to acquire the optimal closing scheme of GVs and RBs when the turbine undergoes full load rejection under rated head conditions. Our test results provide a sound reference for the design and operation of tubular turbine units.

The transient characteristics associated with the machine load rejection process are investigated due to its close relationship with hydraulic facilities’ safety in low-head tubular turbines, especially in double-regulated bulb turbine. Load-rejection transient characteristics of a double regulated bulb turbine during the co-closing guide vanes (GVs) and runner blades (RBs) procedure were numerically and experimentally studied in this paper. The co-adjusting of GVs and RBs is realized through the usage of dynamic mesh technology. During the process, the speed is augmented by 33.9% by the time it reaches its peak value, where the corresponding maximum negative axial force is 43% of the initial value. The three-dimensional (3D) unsteady numerical simulation method reveals that severe impact of backflow from RBs causes significant fluctuation of torque and axial force during the co-closing procedure. A low-pressure vortex rope is also cut off by gravity-dominant pressure distribution, which leads to hydraulic instability and complex flow structure. The system performance characteristics have been obtained through experimental testing, where the dynamic instability during the co-closing procedure has been showcased. This article presents a novel prediction model and a foundations for further transient characteristics studies and prediction for turbine system with adjustable RBs and GVs.

In this paper, the flow field around NACA0015 hydrofoil is calculated under the condition of two-phase cavitating flow to provide a theoretical guidance for reducing the cavitation noise. A modified turbulence model coupled with the Zwart cavitation model is used to calculate the flow field. According to the computed sound source data, the dipole sound pressure distribution diagrams for the extremely short time and the complete time around the hydrofoil under different working conditions are obtained. The sound pressure distribution and the sound pressure amplitude are analyzed in detail. In addition, the field points around the hydrofoil are selected to generate the corresponding frequency response function curves, which are analyzed from the aspects of the trend, the variation and the extreme value. The results show that the dipole characteristics are gradually diminished and finally disappear with the increase of the frequency. At the frequency of the vapor volume fraction fluctuation, the noise level at the field point will have an extreme value.

For most of low-head pump stations, pumps simultaneously undertake important tasks such as flood control, irrigation and drainage where more attention should be paid on involved hydraulic stability. In order to establish a suitable numerical prediction model, two kinds of water surface treatment namely volume of fluids (VOF) and rigid-lid hypothesis (RLH) methods, for upstream and downstream reservoirs, are presented and corresponding results are compared. System transient characteristics during power-off process are predicted, where the obtained maximum runaway speed by VOF method is found to be closer to the one from experimental results. The dynamic parameters of VOF method change slower than those of RLH method and the static pressure peak value is smaller. The usage of VOF method to water dynamics at the reservoir’s free surface makes the water flow in reservoirs relatively smooth, whereas large-scale vortices appear in reservoirs for the RLH method. Moreover, the turbulent kinetic energy is found to be larger if the reservoir’s free surface is not taken into consideration. This article established a novel and accurate prediction model, which otherwise would provide the foundation of further studies in terms of transient characteristics prediction within pumping stations taking into account the air-water interactions.

In this paper, the unsteady natural cavitation and ventilated cavitation are investigated with the large eddy simulation method. The predicted cavity morphology and evolution process before and after ventilation agree well with the available experimental data. The results indicate that in natural cavitation, the formation of a U-type cavity is closely related to the separation of a re-entrant jet and the effect of vortex evolution, while the local high pressure region plays an important role in shaping the appearance of the primary and secondary U-type cavity in the process of moving downstream. During ventilated cavitation, the deflation effect of the air drives the pair of vortices to shed periodically, accompanied by the downstream transportation of vorticity, and promotes the formation of arched air cavities. In the anticlockwise vortex shedding region, the vortex dilatation term has a concentrated distribution on the air-liquid interface which is due to the intense mixing of the phases. Further analysis demonstrates that, in the air cavity fluttering area, the magnitude of the velocity pulsation produces a significant downward tendency due to the gradual weakening of vortex intensity. Moreover, the interaction between vortices and turbulence shows a high degree of consistency in the wake flow.

Tubular pumps are widely used in irrigation and water conveyance projects. However, the operating head of most of these pumps is low, and only a few studies have focused on the design of an efficient tubular pump with a head more than 5 m, which is common in long-distance water supply projects. This work aims to improve the operating head and efficiency of tubular pumps while maintaining a low shaft power. The multi-objective orthogonal optimization method was used to determine the critical parameters of the tubular pump, i.e., blade number, airfoil, blade thickness and guide vane distance, and nine design schemes were selected. Next, by using computational fluid dynamics (CFD), a 3D model of the tubular pumps under different schemes was established, and the results were compared. Subsequently, the range method and weighted matrix method were utilized to find the optimized scheme. In addition, an experimental investigation was performed to verify the simulation and the performance of the designed tubular pump. The results indicated that the optimized scheme improved the operating head to 6.9 m with higher efficiency of 84.2% and a lower shaft power of 27.7 kW. The modeling results were in agreement with the experimental measurements, and the designed tubular pump had a wide range of high-efficiency zones.

In the present investigation, the LES WALE method along with the Zwart cavitation model is utilised to predict the cavitating flow around a Delft Twist-11 hydrofoil and the numerical results show a...

To explore the load impact and instantaneous flow characteristics of a tubular pump under unconventional operating conditions, the runaway condition caused by the unit power failure are investigated. Unsteady three-dimensional (3D) numerical simulation and model test were executed on whole flow system of the pump, where a 3D VOF method was specifically adopted to simulate water surfaces of the upstream and downstream reservoirs. The results of numerical simulation in terms of system performance parameters and runaway speed presented a quite good agreement with the experimental data. During the transient process, both the rotational speed and flow rate of the pump unit were found to rapidly decrease with time until maximum runaway speed (1.51n0) was reached, where however, a time lag of 0.7s between the rotational speed and flow rate has been noticed. The explored increase of pressure pulsations is generally believed to have taken source from incurred water shock waves, where the main pulsation frequencies throughout the whole flow passage were the blade passing frequency (BPF) and its harmonics. Large flow vortical structures immerged within the rear guide vanes when the flow rate decreased to zero, while the same flow vortices appeared within the front guide vanes when the impeller rotational speed gradually fell to zero. This study’s results provide a meaningful reference about pump transient operations, leading to the prevention of associated structural vibrations and possible blade cracks, for safe operations of the pumping stations.

In this research, the cavitating flow around a NACA0015 (National Advisory Committee for Aeronautics) hydrofoil obtained by the large-eddy simulation method is analyzed using the proper orthogonal decomposition (POD) theory. Various fundamental mechanisms have been investigated thoroughly, including the reentrant jet behavior, pressure gradient mechanism, vortex dynamics, and dynamic properties of the hydrofoil. The influence of the vortex dynamics, pressure mechanism, and temporal/spatial evolution is revealed. The POD decomposition indicates that the first four dominant POD modes occupy 97.4% of the entire energy. Based on the vortex force field extracted from the first four single POD modes, it is found that the lift-and-drag characteristics in the cavitating flow are determined by the specific spatial distribution of mode vortex structures. In addition, the coupling of velocity pulsations and pressure fluctuations is carried out to obtain the POD modal pressure gradient field, which reveals that the pressure gradient has a close connection with the cavity evolution. Furthermore, the vortex force and pressure gradient are reconstructed using the first four modes, 17 modes, and 160 modes, which indicates that the low-order POD modes without the impact of small-scale structures and noise can clearly capture the fundamental aspects of the flow field.

Vortex ropes occurred in the draft tube when hydraulic turbines operating at off-design conditions, which can generate pressure fluctuations. Cavitation vortex rope is one of the most harmful factors to the safety of hydroturbines which may induce further pressure fluctuations. A study of the multiphase flow in a model turbine is presented in this paper using the software ANSYS CFX. The main emphasis is spending on understanding the mechanism of cavitation evolution and underlying its correlation mechanism with flow instabilities. The results indicate that two types of pressure variations can be captured with a cavitation rope: 1) The type due to the vortex rope rotating whose frequency is 1/5–1/4 times runner rotating frequency; 2) The type due to cavitation volume surge, whose frequency is less than that of vortex rope rotating. The frequency of pressure fluctuation due to cavitation keep contanst as the cavitation number decreases, while the amplitude much increases. While the frequency and amplitude of the pressure variation caused by votex rope rotating increase a little. Based on vorticity transport equation, the vortex and cavitation have a close relation. Cavitation increases the vortex production as well as the pressure fluctuation frequency caused by the rotation of vortex rope.

Structural simplification and efficient hydraulic performance are key to effectively utilizing ultra-low head water power resources and reducing hydroelectric unit costs. In this study, a computational fluid dynamics (CFD) method was used to predict hydraulic performance of an axial turbine at the Gaoliangjian power station. CFD results agreed well with field test data. Using the same numerical method, a new siphon turbine was then designed based on the original distributor and turbine runner equipment. This study investigated the effect of different siphon outlet passage geometry parameters, runner blade shapes, and distributors on the hydraulic performance of the siphon turbine. The maximum hydraulic efficiency increased to 87.9% under a head of 2.87 m. Finally, the hydraulic performance of the turbine was compared for four different distributor designs after adding an intake sump at the turbine entrance. The bell-shaped distributor with four guide vanes resulted in the highest power output at the lowest head. Therefore, the siphon turbine is a good option for energy conversion in ultra-low water head settings.

Through the numerical simulation of the internal flow field of the thrust bearing, the distribution of the oil membrane pressure field was calculated using the CFD software Fluent. The effect made by inclination angle and rotor speed on the thrust bearing performance was analyzed. The results show that the inclination angle has a strong impact in pumped storage units. Only when the inclination of the circular direction reaches a certain value, with the increase of the circular inclination, the bearing capacity of the oil film gradually increases, and the pressure center moves to the oil outlet. With the increase of the rotor speed, the bearing capacity of the oil film gradually increases, and the pressure center remains unchanged. Therefore, in the limit of the minimum oil film thickness, running at large inclination angles and rotor speed can improve the performance.

Reversible pump turbines (RPT), though praised for their operational flexibility within pumped storage hydropower plants, suffer from large flow instabilities that take source from frequently imposed off-design operating conditions, where the vaneless space (VS) between the runner and guide vanes is claimed to be the base. This study therefore intends to investigate the VS flow instability development mechanism, and the effect of both the machine influx and runner blade number on its transferability to other flow zones. CFD-backed simulations are conducted on ten flow conditions spanning from turbine zone through runaway vicinities to turbine brake, using three runner models with 7, 8, and 9 blades respectively. Results have shown that, while VS pressure pulsation amplitude increased with the decreasing runner blades number, a continuous decrease of machine influx led to a correspondingly dropping VS pressure pulsation level within the Turbine zone before gradually increasing to Runaway and dropping again back to deep turbine brake operating zone. The effect of machine flow conditions and runner blade number on VS flow instability propagation mode to upstream flow zones is more remarkable than the downstream flow zones. This study contributes to a thorough understanding of RPT flow dynamics, especially under off-design operating conditions.

The complex flow field caused by the dynamic stall can affect the operational stability of hydrodynamic machinery. In this paper, the NACA0009 blunt trailing edge hydrofoil is used as the object of study, and the dynamic stall characteristics of the hydrofoil are investigated by using the transition model and the dynamic mesh method. It is found that the hydrofoil deep stall calculated by the transition model is delayed compared to that calculated without the transition model. The hydrofoil dynamic stall can be divided into four stages, initial stage, development stage, stall inception stage and deep stall stage. In the initial stage and the development stage, the lift and drag characteristics are influenced by the shedding vortex. In the stall inception stage and the deep stall stage, the lift and drag characteristics are influenced by the leading edge separation vortex and the trailing edge vortex. The increase of angular velocity and Reynolds number of the dynamic hydrofoil delay the onset of the deep stall while accelerating the boundary layer transition. The research in this paper has a certain guiding effect for the safe and stable operation of hydrodynamic machinery.

Pumped storage plants (PSP) must switch frequently between various working conditions. Moreover, PSPs can fall easily into an S-shaped zone under low water head conditions, especially during back-to-back starting (BTBS), which reduces the stability and safety of unit operation. In this paper, a nonlinear PSP model for BTBS is established by combining an electrical subsystem with a refined hydraulic-mechanical subsystem. The influences of the hydraulic, mechanical, and electrical factors on the BTBS process are investigated quantitatively. Choosing the speed overshoot and speed stable time as the optimization objectives, and considering a variety of constraints, the multi-objective particle swarm optimization (MOPSO) algorithm is introduced to study and optimize two typical startup strategies. The results show that: (1) The parameters of a hydraulic-mechanical-electrical system have a significant impact on BTBS process, and the most unfavorable working condition corresponds to the lowest water head; (2) In the control schemes, a novel constant excitation voltage strategy is proposed based on the multi-objective optimization scheme. Compared with the constant excitation current strategy or single-objective, the optimization strategy proposed can considerably improve the speed overshoot and the speed stable time by at least 68.27% and 3.22% under the worst working conditions. (3) It is further verified that the problem of trapping in the S-shaped region under various working conditions may be avoided by the obtained optimal control scheme. The results give prominence to the effectiveness of the proposed optimization strategy for maintaining the safety and stabilization of PSP operation.

Deciduous broadleaved forests and evergreen broadleaved forests constitute the majority of global subtropical forests. Subtropical vegetation has faced strong anthropogenic pressures, and many natural forests destroyed throughout history have been restored to secondary forests due to various government conservation policies. In early forest restoration, deciduous and evergreen species with significantly different functional traits play different roles and jointly determine secondary forest successional trends, questioning how coexistence and competition between evergreen and deciduous trees profoundly impact community assembly and forest restoration. Although subtropical forest has been seriously threatened, scientific information on how these important ecological processes influence secondary forest regrowth is lacking. We established a 6-ha plot in a subtropical evergreen broadleaved forests in Guanshan National Nature Reserve, southeastern China. All trees individual were stem-mapped, identified to species and measured for diameter at breast height (DBH) and height. Pair-correlation and marked correlation functions indicated that deciduous species are comparatively more vulnerable to density-dependent regulation and size reduction in adjacent individuals during secondary forest succession. The interspecific association between deciduous and evergreen trees in the same DBH class gradually changes from significantly positive to negative as DBH increases, indicating seedling coexistence and competition between large late successional trees at a fine scale. Our results indicate that self-thinning caused by conspecific density-dependent regulation in deciduous trees and interspecific repulsion between evergreen and deciduous trees lead to forest gaps where clustered offspring naturally regenerate to coexist, embodying the important coexistence mechanisms facilitating secondary forest recovery to the zonal climax vegetation types dominated by evergreen species in this region. These findings improve our understanding of the self-recovery mechanisms of subtropical forests in secondary succession and provide important theoretical support to accelerate the future recovery of secondary forests.

Siphon turbines are an attractive type of small-scale hydropower turbines because they can be retrofitted into existing structures where there is already a drop in water elevation. A siphon turbine conveys water from an upper reservoir to a lower reservoir through the use of a siphon structure that goes over the top of the dam. A small, neutrally buoyant autonomous sensor package known as a Sensor Fish was deployed through a siphon turbine at the Head of the U Hydroelectric Project in Idaho, USA. Comparisons were made between the siphon turbine in this study and other low-head turbines that have been studied using Sensor Fish. The Sensor Fish measurements indicate that this siphon turbine can generate nadir (i.e., minimum) pressures during runner passage of 22.4 kPaA, which is much lower than those of other low-head turbine types that have been studied using Sensor Fish and could be potentially harmful to fish species susceptible to barotrauma injury. Severe acceleration events occurred in the wicket gate and runner regions at rates of 12% and 47% respectively. These numbers are comparable or lower than other low-head turbines that have been studied with Sensor Fish. Due to the low nadir pressures measured, stakeholders should determine the presence of any fish species-of-concern in the area that are susceptible to barotrauma, and if so, methods to avoid or reduce fish entrainment such as screening technologies or diversions should be investigated.

Aim Radium-223, a targeted alpha therapy, is approved widely for the treatment of patients with metastatic castrate-resistant prostate cancer, based on a pivotal phase 3 study in predominantly white patients. We investigated the efficacy and safety of radium-223 in Asian patients with castrate-resistant prostate cancer and metastatic bone disease. Methods This multicenter, prospective, single-arm, open-label phase 3 trial evaluated the efficacy and safety of the standard radium-223 regimen (55 kBq/kg every 4 weeks for six cycles) in patients from Asian countries. The primary endpoints were the safety and overall survival. Results A total of 226 patients were enrolled and received at least one dose of radium-223. Median overall survival was 14.0 months (95% confidence interval [CI], 11.2-17.4). Median time to total alkaline phosphatase and prostate-specific antigen progression were 7.5 (95% CI, 6.8-7.7) and 3.6 (95% CI, 3.1-3.7) months, respectively. Median skeletal-related event-free survival was 26.0 months (95% CI, 12.6-not reached). Grade ≥3 treatment-emergent adverse events were reported in 103 (46%) of 226 patients, with anemia being the most common event (34 [15%] patients). Grade ≥3 drug-related treatment-emergent adverse events occurred in 39 (17%) of 226 patients. Serious treatment-emergent adverse events were reported in 65 (29%) of 226 patients. Seven (3%) patients had an adverse event leading to death; none were considered to be related to radium-223. Conclusion The results of this study support the use of the standard radium-223 regimen for the treatment of Asian patients with castrate-resistant prostate cancer and symptomatic bone metastases.

The water-guide bearing lubricating oil system of pumped storage unit is prone to oil dumping and oil spillage during the start-up of the unit, which seriously threatens the safe and stable operation of the unit. In this study, a three-dimensional unsteady numerical simulation is performed to investigate the causes of oil dumping and oil spillage of a water-guide bearing lubricating oil system of a pumped storage power plant unit based on the VOF (volume of fluid) multiphase flow model and Realizable k-ε model. The unsteady flow characteristics inside the rotating oil basin and pump-type Pitot tube during the start-up process are analyzed. The results demonstrate that the change of the external characteristics of the lubricating oil system can be divided into two stages, the initial formation process of the lubricating oil flow and the stable circulation process of the lubricating oil flow. In the initial formation process, the pressure inside the rotating basin is uniformly distributed in the circumferential direction, and a high-pressure zone is generated near the inlet of the pump-type Pitot tube, driving the lubricant flow to the stationary basin above; in the stable flow cycle process, the internal lubricant flow velocity gradually decreases along the radius direction, and a large vortex zone appears behind the pump-type Pitot tube and at the inlet of it. This phenomenon leads to the lubricating oil pressure here to be lower than the saturation vaporization pressure, which may trigger lubricating oil atomization and then overflow from the seal ring. This study is committed to provide theoretical analysis and engineering reference for the investigation of the causes of oil dumping and oil spillage in the lube oil system of water guide bearings of pumped storage units.

During the past 30 years, the global forest area has been subject to a continuous increase in planted forests and a decline in natural forests, raising significant concerns about biodiversity protection. Once these plantations are abandoned due to changes in conservation or forest management policies, can they recover to the same state as natural forests during secondary succession? The key ecological processes supporting the stable coexistence or competitive elimination mechanisms between post-abandonment plantations and natural secondary forest tree species are still poorly understood and may be the decisive ecological processes driving secondary forest restoration. A 12-ha long-term forest plot was established in an abandoned Chinese fir plantation that has been protected under an in situ protection policy for 40 years. In total, 66,317 individual trees were stem mapped and identified at the species level, and the spatial survival strategies and species coexistence mechanisms between Chinese fir and natural secondary forest tree species were investigated. The results showed that the spatial survival strategy of Chinese fir could effectively trade off a high conspecific density-dependent mortality rate of individuals during the early stage of secondary succession for the long-term survival of the whole population, which promoted its dominance during later stages of succession. By contrast, although the higher survival rate and larger intraspecific aggregation scale of natural secondary forest individuals favored their survival during initial colonization, this spatial survival strategy might occur at the cost of neglecting suitable habitats and the loss of competitive advantages at the later stage of succession. Regarding interspecific competition, the asymmetric competition process further ensured the advantages of Chinese fir in individual size growth and increased the competitive advantage of Chinese fir over natural secondary forest tree species by exclusion through interspecific competition during the later secondary succession stage. Our results suggest that implementing a forest recovery program or an in situ protection policy based on post-abandonment monoculture plantations may involve great uncertainty about whether the goal can be achieved. Specifically, although this strategy could quickly increase forest coverage and restore the forest landscape, it may also create difficulties in restoring the forest to its original state.

The Hydraulic turbine efficiency is traditionally calculated by the pressure drop between the inlet and outlet. But this method cannot determine the detailed energy loss distributions along the flow passage. Entropy production theory can predict and exhibit the irreversible energy loss distribution intuitively. An advanced entropy production diagnostic model (EPDM) with phase transition (EPDMS) is introduced in this study to evaluate the irreversible energy loss in cavitating flows. The EPDM method is based on homogeneous equilibrium model (HEM) without interface slip velocity while EPDMS is based on two fluid model (TFM) with the consideration of slip velocity and interface forces. At operating point guide vane opening (GVO) 20.07, the relative error of EPDM for efficiency calculation is 6.87% and the relative error of EPDM is 3.05%. In EPDMS, the interaction between cavitation and entropy production rate (EPR) is defined and interface EPR (IntE) has a considerable proportion of total EPR in EPDMS. With the HEM method, the underprediction of the turbulent eddy viscosity results in the underestimation of irreversible energy loss. In essence, the intensive mass transfer process in cavitation flow induces the generation of IntE and corresponding irreversible energy loss directly.

In recent years, distributed renewable energy-generation technologies, such as wind and solar, have developed rapidly. Nevertheless, the utilization of ultra-low-head (ULH) water energy (i.e., situations where the hydraulic head is less than 3 m or the water flow is more than 0.5 m/s with zero head) has received little attention. We believe that, through technological innovations and cost reductions, ULH hydropower has the potential to become an attractive, renewable, and sustainable resource. This paper investigates potential sites for ULH energy resources, the selection of relevant turbines and generators, simplification of civil works, and project costs. This review introduces the current achievements on ULH hydroelectric technology to stimulate discussions and participation of stakeholders to develop related technologies for further expanding its utilization as an important form of renewable energy.

To provide theoretical basis for cavitation noise control, the cavitation evolution around a hydrofoil and its induced noise were numerically investigated. A modified turbulence model and Zwart cavitation model were employed to calculate the flow field and predict the cavitation phenomenon accurately. Then, the acoustic analogy method based on the Ffowcs Williams-Hawking (FW-H) equation was applied to analyze the cavitation-induced noise. Seven cavitation numbers were selected for analysis. Acoustic power spectral density (PSD) and acoustic pressure were investigated to establish the relationship between cavitation number and their acoustic characteristics. It was indicated that as cavitation number decreases, cavitation cycle length gets shorter and the magnitude of acoustic power spectral density increases dramatically. One peak value of acoustic power spectral density induced by the extending and retracting of leading-edge cavitation can be obtained under sheet cavitation conditions, while under cloud cavitation, two peak values of acoustic power spectral density can be obtained and are induced by superposition from leading-edge cavitation and trailing vortex.

Cavitation and system instability are the most common problems occurring in hydraulic power systems, especially operated under part-load conditions. Previous research show that when the hydraulic turbine operates apart from designed conditions, such as part-load conditions, a helical vortex rope occurs from the runner exit, and usually generates severe pressure oscillations. Cavitation usually appears and turns the rope to become a two-phase cavitation rope. The occurrence of cavitation rope is believed to be the main reason of the severe pressure oscillations. Based on a new multiphase flow simulation method re-developed in ANSYS CFX, this paper did the runner modification by using grooves and made the investigation of pressure fluctuation alleviation in a hydraulic turbine at different cavitation numbers. The behavior of cavitation rope and the pressure fluctuations induced by cavitation under typical part load conditions with modified runner were analyzed in present research. The results show that besides the pressure fluctuation induced by the rope rotating, cavitation induced a new pressure fluctuation with a lower frequency. For the embedded analysis the results show that the modified runner can decrease the vortex rope eccentricity and increase the vortex core pressure and finally alleviate the two types of pressure fluctuations. Also, the turbine efficiency has a little rise when equipped with the modified runner.

The utilization of pump as turbines (PATs) within water distribution systems for energy regulation and hydroelectricity generation purposes has increasingly attracted the energy field players’ attention. However, its power production efficiency still faces difficulties due to PAT’s lack of flow control ability in such dynamic systems. This has eventually led to the introduction of the so-called “variable operating strategy” or VOS, where the impeller rotational speed may be controlled to satisfy the system-required flow conditions. Taking from these grounds, this study numerically investigates PAT eventual flow structures formation mechanism, especially when subjected to varying impeller rotational speed. CFD-backed numerical simulations were conducted on PAT flow under four operating conditions (1.00 QBEP, 0.82 QBEP, 0.74 QBEP, and 0.55 QBEP), considering five impeller rotational speeds (110 rpm, 130 rpm, 150 rpm, 170 rpm, and 190 rpm). Study results have shown that both PAT’s flow and pressure fields deteriorate with the machine influx decrease, where the impeller rotational speed increase is found to alleviate PAT pressure pulsation levels under high-flow operating conditions, while it worsens them under part-load conditions. This study’s results add value to a thorough understanding of PAT flow dynamics, which, in a long run, contributes to the solution of the so-far existent technical issues.

To obtain the dynamic parameters variation characteristics of a model tubular turbine during the load rejection process, a model test method was designed and carried out in this paper. Firstly, the model test system, the test method and the model tubular turbine parameters were introduced. Then, the experiments of different schemes were performed and the results were analyzed. Evidently, the closing rules of guide vanes and runner blades have influence on the quality of transient process. When the guide vanes undergo linear needle closure law, the effect of prolonging the blade closing time on reducing the maximum speed appreciation and the maximum reverse water thrust is obvious, and when the guide vanes is closed in two stages, the longer the blade closing time, the lower the maximum reverse hydraulic thrust value. With the same closing law, the segmental closure law with guide blade first fast and then slow is more obvious than the linear needle closing law in reducing the maximum reverse water thrust, and the selection of closure segment point of guide vanes has a certain effect on the appreciation of the maximum rotating speed. Thus, the model test method could be used in transient operation improvement at hydropower plants.

The objectives of this research are to apply entropy production theory into cavitating flows and investigate dynamic characteristics of entropy production rate (EPR). A thermodynamic cavitation model and a density corrected turbulence model was adopted to this simulation around NACA0015 hydrofoil. Entropy production as a new method for evaluating energy performance is applied on thermodynamic cavitating flows. Cavitation effects on entropy production are firstly derived and revealed. Different entropy production terms by direct dissipation (EPDD), turbulent dissipation (EPTD), wall shear stress (EPWS), mean and fluctuating temperature gradients (EPMT and EPFT) were established in unsteady cavitating flow at 343 K to understand the interactions between cavitation and entropy. The results indicates that entropy production has strong association with cavitation. And entropy production rate by cavitation (EPRC) was derived firstly to evaluate the effects of phase change on entropy production rate. The entropy production rate by cavitation mainly focuses on the interface of cavity where there has intensive mass transfer procedure. Total entropy production rate (TEPR) mainly focuses on leading edge of hydrofoil, rear of attached cavity, detached cavity. Direct and turbulent entropy production rate are two main part in thermal cavitating flows. Direct entropy production can better reflect how total entropy production is distributed. Velocity gradients and phase change are two dominate factors controlling entropy change. In one cycle, total entropy production firstly decreases to its minimum and keeps stable to the inception stage of detached cavity collapse, then increases and fluctuates with cavity collapse.