HYDRODYNAMIC LOADS ON THE WALLS OF A TURBINE BLOCK WITH A COUNTER VORTEX DAMPER

A bidirectional axial flow pump can realize bidirectional pumping, which has a wide application prospect in coastal low-head pumping stations and water jet propulsion systems. In this paper, a typical bidirectional axial flow pump is taken as the research object, and the hydraulic model of the bidirectional axial flow pump is manufactured. The hydrodynamic characteristics of the bidirectional axial flow pump are tested on the high-precision hydraulic mechanical test bench, including the positive and negative directions. In the experiment, multiple pressure pulsation monitoring points were arranged in the impeller chamber, and the pressure fluctuations in the pump under a total of 42 flow conditions were measured by a micro pressure pulsation sensor, involving 21 working conditions of forward operation and 21 working conditions of reverse operation. According to the experimental results, the hydrodynamic characteristics, especially the pressure pulsation characteristics in the pump, of the two-way axial flow pump under positive and negative operation are comprehensively compared and analyzed, and the energy characteristics and the propagation law of pressure pulsation of the two-way axial flow pump under positive and negative operation are revealed. The research results provide an important reference for the safe and stable operation of coastal bidirectional axial flow pump stations.

The free discharge through the turbine is applied in the course of construction of hydro power plant or in case of excessive water inflow during floods or emergency situations. The experimental and numerical investigation of flow-induced pressure pulsations in hydraulic turbine draft tube at free discharge was performed using a special setup for suppression of draft tube surge. Such special equipment in draft tube cone as fins and “spider”-like units was considered for reducing these pressure pulsations. The paper considers influence of these units on vortex structures and pressure pulsations in the draft tube in several regimes.

In hydraulic turbines, several flow instabilities can take place inside the draft tube cone during off-design and transient operating conditions such as the rotating vortex rope which can severely damage the structure if sustained in time. In the frame of the AFC4Hydro H2020 research project, an extensive measurement campaign has been carried out to monitor and predict this rotating vortex rope phenomenon in a reduced scale Kaplan turbine model at the Vattenfall Research and Development facility in Älvkarleby, Sweden. The hydraulic turbine model has been operated in propeller mode with a fixed blade angle corresponding to its best efficiency point. Several sensors have been placed along the test stand to monitor vibrations, strains and pressures. Concretely, the present paper assesses the performance of using Fiber Bragg Grating sensors to measure the strains induced on the draft tube cone walls with high-spatial resolution in three different zones of influence: the upper and lower flanges and the vertical cone wall between the runner outlet and the elbow. To do so, a total of 3 arrays embedding a total of 48 Fiber Bragg Grating sensors were glued inside three grooves previously machined on these particular areas of the draft tube cone. Analysing the frequency response of the different Fiber Bragg Grating sensors, the strain patterns induced by the rotating and plunging components of the rotating vortex rope have been precisely determined. Moreover, their impacts at the different part load conditions tested have also been quantified.

The diversity of energy conversion sources in the current energy market increases the demand for stabilizing the electrical grid through ancillary services, frequency and power regulation from the facilities. Pumped-storage units with reversible pump-turbines or ternary sets constitute the currently most advanced solution for providing these services. This implies that pumped-storage units are required to operate in larger head and power ranges than before. In order to increase their flexibility in pump mode, variable speed units have been applied more frequently with additional challenges for the operating range in pump mode.The extension of the operating flexibility in pump mode makes use of a large portion of the model pump characteristic curve, especially in the case of variable speed units. Important challenges to the hydraulic development are among others the cavitation behaviour, hydraulic stability and pressure pulsation level. This study concentrates on the pressure pulsations in pump mode, which are of great relevance for the machine smooth operation.The pressure pulsations in a regulated radial reversible pump-turbine with low specific speed are numerically simulated with computational fluid dynamics (CFD) for several points along the complete operating range of the pump characteristic curve. The finite volume model includes the complete hydraulic machine from draft tube to spiral case and hybrid turbulence models were used, in this case scale adaptive simulation (SAS). The numerical simulation offers the possibility to assess different flow quantities at any point of the finite volume model, providing additional data to the experimental model test results.The integral quantities, e.g. head, flow and efficiency, were compared to the model test results to validate the numerical model. The simulated pressure pulsation amplitude and frequency were also compared to the measured pressure pulsations at the model at the available measuring locations in the spiral case, vaneless space and draft tube cone. After the validation, the computed flow fields were used to derive the pressure pulsation amplitude at other machine locations and components, e.g. at the runner.

Supplying consumers with continuous electricity is one of the urgent problems of today. The main part of electricity is produced by hydroelectric stations. The perfect operation of the main electrical equipment of hydroelectric power stations is related to the reliable operation of the electrical equipment in operation. The flawless operation of power transformers in operation at hydroelectric power stations is evaluated by their technical condition. The technical condition of power transformers is determined by their electrical and non-electrical indicator values. In this article, a simulation model for determining the value of the technical condition of power transformers in operation at hydroelectric power stations using fuzzy logic has been developed.

The presence of excessive swirl at the runner outlet in Francis turbines operating at part load leads to the development of flow instabilities such as the rotating vortex rope (RVR). The presence of RVR causes severe pressure pulsations, power swings, and fatigue damage in the turbine unit. Air and water injection in the draft tube have been reported to reduce the detrimental effects of RVR formation in the Francis turbines. Air injection is one of the oldest and most widely used methods. In contrast, water jet injection is a relatively new methodology. The present work reports the numerical simulations performed to compare the respective effectiveness of these methods to mitigate the RVR and the related flow instabilities. The efficacy of the two methods has been compared based on the pressure pulsations and pressure recovery in the draft tube cone. The results show that the air and water injection influence the draft tube flow field in different ways. Both air and water injection led to a reduction in pressure pulsation magnitudes in the draft tube cone. However, the air injection led to a negative pressure recovery while the water injection improved the draft tube action.

Francis turbines have been running more and more frequently in part load conditions, in order to satisfy the new market requirements for more dynamic and flexible energy generation, ancillary services and grid regulation. The turbines should be able to be operated for longer durations with flows below the optimum point, going from part load to deep part load and even speed-no-load. These operating conditions are characterised by important unsteady flow phenomena taking place at the draft tube cone and in the runner channels, in the respective cases of part load and deep part load. The current expectations are that new Francis turbines present appropriate hydraulic stability and moderate pressure pulsations at overload, part load, deep part load and speed-no-load with high efficiency levels at normal operating range. This study presents series of investigations performed by Voith Hydro with the objective to improve the hydraulic stability of Francis turbines at overload, part load and deep part load, reduce pressure pulsations and enlarge the know-how about the transient fluid flow through the turbine at these challenging conditions. Model test measurements showed that distinct runner designs were able to influence the pressure pulsation level in the machine. Extensive experimental investigations focused on the runner deflector geometry, on runner features and how they could reduce the pressure oscillation level. The impact of design variants and machine configurations on the vortex rope at the draft tube cone at overload and part load and on the runner channel vortex at deep part load were experimentally observed and evaluated based on the measured pressure pulsation amplitudes. Numerical investigations were employed for improving the understanding of such dynamic fluid flow effects. As example for the design and experimental investigations, model test observations and pressure pulsation curves for Francis machines in mid specific speed range, around nqopt = 50 min−1 are reported, analysed and commented here. The analysis of experimental results allowed the identification of designs and configurations, which can improve the machine stability.

An improved source for x-ray lithography is described which is capable of significantly enhanced brightness through an improved cooling system. In the normal Gaines source which has an inverted cone shaped anode, the cone walls are straight, and the water flows in a narrow channel coaxial with the anode. Anode cooling occurs with water in the nucleate boiling regime, and maximum heat flux is set by the critical density of vapor bubbles at which coalescence occurs. By providing the flow of water around the anode with a concave upstream curvature, huge inertial forces create instantaneous phase separation. As a result the power density at which burnout occurs is substantially increased and moreover, significantly stabilized. In addition the use of a shaped anode allows for a self-guiding jet with no channel, which eases the mechanical design considerably. Measurements of the anode temperature excursion indicate a temperature rise of 450 °C with 6.2 kW in a 3 mm spot (25 kW/cm2). It is anticipated that fluxes two to three times higher may be accommodated. The Pd Lα line output (2.84 keV) was measured as a function of the incident power. It is found that Pd Lα generation does not follow the common power law for Kα radiation of most materials. The behavior can be explained in terms of the shallow incident beam angle and radiation take off angle. The absolute conversion efficiency of Pd Lα was measured at 20 keV and found to be 34 μW/W-sr in this gun configuration.

At this time, a large number of hydraulic turbomachinery installations are ageing, so that they need refurbishement to increase their efficiency and their associated output power. The items that need refurbishement are mainly the runner and the guide vanes. The draft tube and the spiral casing are generally not modified, for cost and safety reasons. An unsuitable match between the new runner and the old draft tube can lead to an unfavourable flow behavior and an efficiency drop when the hydroelectric plant works at off-design conditions, due to the rapidly changing user load conditions. Moreover, in non-optimum operating conditions, the draft tube can be the origin of unstabilities that prevent the machine exploitation. The understanding of the flow in the draft tube is therefore very important for the prediction and the control of the machine stability. The flow in the draft tube is complex, unsteady and turbulent because of its rotating nature and of the draft tube's geometry. In order to increase the understanding of the flow physics, analyses of the steady and unsteady pressure fields on the draft tube walls are lead through extensive pressure measurements in the whole draft tube. The investigation is divided in two parts. The first one concerns the analyses of the pressure measurements at the operating points near the optimum (BEP) in order to understand the recovery coefficient break-off when the flow rate increases. A particular evolution of the steady pressure field appears following the operating points around the BEP. Consequently, the flow is distributed between the 2 channels of the draft tube according to each operating point. As for the unsteady phenomena, the fluctuating field in the cone of the draft tube shows 2 components : a rotating component at the runner frequency fn and a synchronous component at 20fn resulting from the rotor-stator interaction. The influence of the spiral casing on the fluctuating pressure is pointed out by representing all phase average signals in the same absolute angular position of the runner. Unsteadiness of random nature at very low frequency, below 0.3fn, appears as well. These fluctuations propagate from the elbow to the 2 channels in the draft tube. Correlations between the steady and unsteady results are observed during the analysis. The second part concerns the analysis at the low discharge operating points. An influence of the vortex volume, from a hydrodynamic and acoustic point of view, has been found in the turbine operation for 3 values of the Thoma number σ. For these 3 pressure levels, the turning pressure field due to the vortex rotation is completely deformed by a synchronous pressure field at the same frequency. This field influences the magnitude of the fluctuations at the wall and mainly in the phase velocity of the vortex. At low σ, the big volume of the biphasic vortex interacts with the draft tube in such a way that the elbow becomes the source of strong pression oscillations that propagate to the upstream and to the downstream of the draft tube and dangerously towards the pipes of the test rig system. At mean σ, the volume of the biphasic vortex decreases and causes a regular pressure field in the draft tube and the strong oscillations disappear. At high σ, the vapor phase disappears completely and the comparison between the measurements and a monophasic numerical calculation shows good consistency in the cone of the draft tube. Thanks to this computation it is possible to explain the fluctuations shape at the cone walls.

During the flood season, Francis turbines often operate under low-head and full-load conditions, frequently experiencing significant pressure pulsations, posing potential threats to the safe and stable operation of the units. However, the factors contributing to substantial pressure pulsations in Francis turbines are multifaceted. This paper focuses on a mixed-flow hydroelectric generating unit at a specific hydropower station. Field tests were conducted to investigate abnormal vibrations and hydraulic pressure pulsations under low-head and full-load conditions. Utilizing the Navier–Stokes equations and the RNG k-ε turbulence model, the unsteady flow field within the turbine under these conditions was calculated. The results indicate that the abnormal pressure pulsations detected in the bladeless zone between the wicket gates and the turbine inlet are due to operational points deviating from the normal operating range of the turbine. When water flows at a large inflow angle, striking the turbine blade heads, it leads to significant flow separation and vortex formation at the back of the blade inlet edges, causing severe vibrations in the hydroelectric generating unit. These findings provide a basis and assurance for the safe and stable operation of the power station.

In order to assess the effectiveness of reconstructed energy dissipation facilities (EDFs) in open channels at hydropower stations, hydraulic prototype observation (HPO) tests are conducted to investigate the characteristics of discharge flow and the dynamic response of hydraulic structures during sluice opening periods. While hydraulic model tests (HMTs) are commonly utilized in laboratory settings to study these characteristics, experimental conditions cannot fully replicate the real-world operations of such structures. HPO tests are employed to examine flow patterns, free water surface fluctuations, and pulsating pressure changes in open channels under varying flood discharge conditions (FDCs). Flow patterns in open channels are recorded via video; free water surface fluctuations are measured using total-station and laser rangefinder instruments; and pulsating pressure is monitored with pressure sensors and data collection systems. Flow pattern observations concentrate on addressing adverse water flow phenomena, such as turbulence, surging, and backflow. The examination of free water surface fluctuations aims to verify whether the height of the guide wall along the open channel fulfills the necessary requirements and assess the effectiveness of energy dissipation of the EDF. To comprehend the variations in pulsating pressure within the continuous sill and the base slab, nine measurement points were established across three sections perpendicular to the continuous sill’s axis on three distinct elevation levels. Additionally, three measurement points were positioned on the reinforced base slab along the open channel’s axis. The findings indicate that the impact on the continuous sill caused by discharging water is more severe when the discharge rate of a single sluice gate reaches 500 m3/s than in other FDCs. To ensure the safe operation of open channels during flood discharge, the discharge rate for each sluice gate should be reduced to 250 m3/s. The dominant pulsation induced by discharge flow falls within the low-frequency range, resulting in minimal adverse effects on the stilling basin and guide wall. The flow pattern within the stilling basin remains stable under various FDCs, with no significant adverse hydraulic phenomena observed. Parameters, including free water surface fluctuations and pulsating pressure variations, lie within acceptable ranges. These observations suggest that the arrangement of the reconstructed energy dissipation facilities is generally effective following technical reconstruction.

Environmental flow is a hot and current issue in water resources management in many countries in the world. In upstream river basins, it introduces a new constraint to hydropower sector. In the implementation stage of environmental flow economic aspects play a key role in river basin management. Economic measures are useful tools in management because they give strong incentive to conventional water users to change their behavior. We can take advantage of economic measures such as levy and subsidy to achieve consensus among all stakeholders in river basin management. A subsidy system for setting environmental flow release from hydropower stations is proposed based on a benefit function of environmental flow formulated in terms of flow rate. Under this subsidy, each hydropower station estimates the possible amount of subsidy to compensate the power production loss by flow release. Consequently, environmental flow is determined by optimum decision procedure by each hydropower station. This paper provides decision support system to water resources management in upstream river basins. Economic impact of management policy is large in some regions but not so much in others. We clarify that regional variation of economic impacts is a function of fraction of hydropower in total electric output, hydrological condition, and size of local economy. The subsidy system developed in this study is able to provide an economic measure to mitigate the inequity.

We applied local fuzzy reconstruction as deterministic nonlinear short-term prediction to data for water flow into hydroelectric power stations. Such prediction involves complex natural phenomena, and conventional hydraulics-based mathematical models do not produce satisfactory results. When a neural network is used, its construction cannot be easily determined, so extra neural networks must also be provided separately, based on experts' opinions. To solve these problems, we held that if time-series data of the inflow rate for hydroelectric power stations exhibits deterministic chaos, the status in the near future is predicted. Typical outflow analysis using conventional mathematical models is described briefly, followed by local fuzzy reconstruction, then results are given from applying this to water flow prediction.

With the development of economy and the improvement of human living standards, the demand for energy will only continue to grow. As one of the main renewable energy sources, River energy has made great progress. The equipment of river kinetic energy generation is different from that of conventional large and medium-sized high dam hydropower stations because of the different energy conversion modes. If the technology and equipment of Gaoba Hydropower Station are mature, the river kinetic power station system and its series technology and equipment are still in the primary stage of development. Different water flow generation methods use different platform positioning systems. In order to collect unstable water flow energy, the water flow power generation device is required to convert the mechanical energy in the water flow energy into electricity that can be used by two-stage energy conversion. Based on the fluid mechanics analysis, this paper determines the factors related to the energy conversion efficiency of the primary conversion device and the relationship between the influencing factors. I hope that I can make some contribution to the development of renewable energy.

The flow instabilities and pressure pulsations at Part load (PL) are detrimental to the turbine’s life and performance. The present work reports the combined water and air injection in the draft tube (DT) cone. The water is injected through the center of the hub cone using a nozzle with a diameter of 12.7 mm. The air is admitted through the DT periphery. The water injection percentage 0.5% to 2% of the turbine inlet flow rate, and the air is injected at 0.5% to 2.5%. The spectral analysis assesses the pressure amplitude and dominating frequency affected by the combined water and air jet injection. The effect of combined air and water jet injection on synchronous (plunging) and asynchronous pressure pulsations (rotating) is analysed at two different measurement planes of the draft tube cone.