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[en] Although the technology of pump-turbines is generally well known the operation is still affected by flow phenomena that are quite complex and not fully understood. One of these phenomena is the S-shape instability which occurs in turbine mode at low load operation, close to runaway conditions. The instability results in an S-shape of the turbine characteristics and complicates the synchronization of the machine. Numerical investigations performed in the past indicated that the occurrence of turbine instabilities is connected with the appearance of rotor-stator interactions, and backflow regions in the vane less space between guide vane and impeller. This paper presents the results and conclusions of experimental investigations of pump-turbine instabilities carried out to find a practical explanation for the flow phenomena responsible for the appearance of the S-shaped characteristics. In the scope of a joint research project with Andritz Hydro, the Institute for Hydraulic Fluidmachinery at Graz University of Technology optimized an existing 4-quadrant test rig for an experimental investigation at off design conditions featuring the possibility for adjusting stable operation of instabilities. All the experimental investigations were based on IEC60193-standard using a pump turbine model provided by Andritz Hydro AG. In addition to the standard measurements of flow rate, head and efficiency the interaction between model and its hydraulic environment were analysed by dynamic pressure sensors. Additional pressure sensors integrated in the guide vane apparatus were used to investigate pressure distributions in the model. Particle Image Velocimetry (PIV) allowed the measurement of the velocity field in the vane less space between impeller and guide vanes and in the environment of two single guide vanes. The experimental investigations were focused on operation points in the S-shape region of the characteristics. For each operation point 190 double images for 20 rotor-stator positions were taken which allowed an analysis of a complete blade channel. The combination of PIV and pressure measurements in the model enabled a structured experimental analysis of the flow phenomena at low load off- design operation and allowed an improved understanding of the physical background of the occurrence of the instability in turbine mode
[en] In order to get the accurate hump characteristic curve of a pump turbine in pump mode, three dimensional steady simulations were carried out using SST k-ω turbulence model with cavitation model and without cavitation model under different operation condition points with 19 mm guide vanes opening. A refinement grids were generated to adapt the turbulence model. The results obtained with cavitation model show a better agreement with experiments. The detailed analysis was undertaken to find out the relationship between the cavitation and hump region. It is concluded that the hump characteristic is related with cavitation
[en] The causes of resonance of a certain model pump-turbine unit during startup process were investigated in this article. A three-dimensional full flow path analysis model which contains spiral case, stay vanes, guide vanes, runner, gaps outside the runner crown and band, and draft tube was constructed. The transient hydraulic excitation force of full flow path was analyzed under five conditions near the resonance region. Based on one-way fluid- structure interaction (FSI) analysis model, the dynamic stress characteristics of the pump-turbine runner was investigated. The results of pressure pulsation, vibration mode and dynamic stress obtained from simulation were consistent with the test results. The study indicated that the hydraulic excitation frequency (Z_g*f_n) Hz due to rotor-stator interference corresponding to the natural frequency of 2ND+4ND runner mode is the main cause of resonance. The relationship among pressure pulsation, vibration mode and dynamic stress was discussed in this paper. The results revealed the underlying causes of the resonance phenomenon
[en] Conventional representations of the various operation modes of a pump-turbine (4-quadrant characteristics) have important disadvantages. While curves of Q11 vs n11 have singularities at E=0 and multiple values in the 'unstable' ranges, the curves EnD(QnD) get singular at n=0. As a remedy, one may split the characteristics into separate parts, and switch between them. Another approach introduced by P. Suter (1966, ) defines a different set of variables which avoids singularity and always remains unique-valued. Suter described this artifice for non-regulated pumps; but using it for regulated machines without modifications is not practical due to large distortions at small guide vane opening. A decisive improvement has been described by C.S. Martin . It avoids the distortion of the head-vs-flow curves at low load. The present paper describes how further improvement is possible, in particular with regard to the representation of torque. A modified torque parameter is obtained by subtracting the shutoff torque; this parameter can be handled in the same practical way as the discharge. Other improvements concern the correction for leakage at small guide vane opening, and the treatment of very small and zero opening. These details are concerned with the problem of closed gate where Suter's concept does not work. Applications are demonstrated, not only how to represent the hydraulic performance (head vs. discharge and torque vs. discharge), but also for other characteristics, such as the development of pressure and pressure pulsation in various locations, or the steady-state and unsteady guide vane torque. The advantage of a set of continuous, single-valued functions for all those physical properties greatly simplifies computation of their behavior during transients. Moreover, the, Suterized' properties of pump-turbines of different specific speed are less different from each other than the conventional ones, a fact that facilitates application of available test data for later projects.
[en] In the design process of pump-turbines, both in pump and turbine mode, the assessment of the components matching is very important. In order to be fast in this task, the usual procedure is based on steady-state methods, like the frozen-rotor or the mixing-plane method. The frozen-rotor approach is straight forward and relatively easy to implement, but can produce unphysical behavior, mainly depending on the relative position of the components. On the other hand, the mixing-plane has a more physical background, delivering to the downstream component the mixed-out state of the upstream flow. On how the mixed-out state is computed and imposed to the downstream component there are different methodologies. In the present paper a novel, fully-implicit mixing-plane method is presented and applied to pump-turbine applications, both in pump and turbine mode. The major advantage of this approach is its robustness, including the ability to handle back flow at the interface, and accuracy. Compared to currently available methods, both in proprietary and commercial codes, the implicit approach leads to a consistent treatment of the interface, enforcing natively the idea of the mixing-plane, i.e. constant spanwise-distribution of the quantities. This allows to obtain excellent results also at part- and over-load
[en] 'Full text:' There are advantages to power generation at or near the points of consumption and this is still true for low carbon sustainable power sources, including wind. Consequently, there is interest in wind power generation in cities and suburbs. The potential now exists for realistic power small-scale generation in building mounted turbines. This presentation provides the benefits and obstacles to their use, as well as details of such turbines and the design and operations requirements for them. The main issues associated with locating turbines in cities and suburbs are: the highly turbulent, unsteady wind in the urban/suburban environment produces lower power outputs; vibration is a large concern on mounting turbines on buildings, and safety (turbine failure or even just ice shedding) with pedestrians below. Past and current thinking has just been straightforward in that it is not worth it, and the previous attempts at simply mounting small-scale turbines on rooftops has done more harm than good to the reputation of the small wind, and wind in general, industries. Recently there has been a reconsideration of urban small wind led by reputable companies such as Quiet Revolution (UK), Turby (NL) and Cleanfield (Canada) combined with academic research. A common feature of all of these companies is the use of vertical axis turbines (VAWTs) to help deal with the highly turbulent, unsteady urban winds. Large-scale VAWTs enjoyed a brief flurry of interest in the 1970s and 80s with large amounts of research done at Sandia and NRC in Canada. Vibration and fatigue in the large-scale turbines were among the issues that led to their decline. These, particularly vibration, remain issues for small-scale turbines, but there are some mitigating strategies available. These are now leading to the development of reputable, practical and reliable turbines that can become part of the urban/suburban environment. (author)
[en] The concept Monitoring applied to the Wind Energy technology is similar to the definition used in other branches of Science or Engineering, this is knowing values of variables which have to do with a mechanic system, in our case a wind turbine. These mentioned parameters may have different relationships to our wind turbine; some of them come from the environment the machine is operating in, others, are a measure of how properly the machine is working, and finally, the rest are an assessment of the systems health during its life. In this chapter we will answer questions such as: What do we need to measure? Why is Monitoring mandatory (from the different points of view of people involved in this world)? How can we measure a wind turbine depending on our objectives (Technic, tools, guidance, recommendations, etc.)? And finally What can we expect in the near future? The author wants the reader to keep the idea in mind that Monitoring means the richest and most accurate knowledge on wind turbine's operation (Its environment, performances or health). This is the first step that allows us to optimize the operation mode of the machine and improve it (design, manufacturing, even the used modeling tools). When there is so much money involved, this fact becomes a must. (Author)
[en] Highlights: • The vertical wind has an impact on the power output of a SVAWT in an urban area. • 90% of the power is generated when the vertical angle is less than 45°. • Efficiency is over 40% only when the horizontal wind speed is more than 8 m/s. • Ratio of the power generated by the unknown direction is between 31.1% and 8.4%. • Turbulence intensity converges at about 30% when the wind speed is more than 8 m/s. - Abstract: The goal of this study is to investigate the performance of a small vertical-axis wind turbine at an environment with the turbulence intensity more than 30%, particularly on the influence of the vertical wind, the vertical angle, the wind with the unknown direction, the horizontal wind speed, and the turbulence intensity on the power output, which are seldom reported before. The results show that more than 90% of the power is generated when the vertical angle is less than or equal to 45°. The vertical wind speed has the obvious influence on the power when the horizontal wind speed is between 5 m/s and 8 m/s. The percentage of the power generated by the wind with the unknown direction decreases from 31.1% to 8.4% as the horizontal wind speed increases from 4 m/s to 9 m/s. The efficiency is over 40% only when the horizontal wind speed is over 8 m/s. The higher turbulence intensity increases the power at the lower wind speed, but decreases the power at the higher wind speed. Furthermore, the results can be used as a reference for the improvement of aerodynamic characteristics, efficiency, CFD simulation and the location selection of a vertical-axis wind turbine.
[en] The measurement of wind turbine noise at an immission point at a large distance from the turbine is very often hindered by the high contribution of the ambient noise and of the wind-induced noise in the microphone. The use of a 2-microphone technique for the measurements could reduce the measured contribution of the ambient noise and the wind-induced microphone noise without the suppression of the measured wind turbine noise. The merits of this technique were assessed experimentally, both in the time domain and in the frequency domain. It is concluded that the measured contribution of the ambient noise and wind-induced microphone noise is indeed reduced significantly. However, also the measured contribution of the wind turbine noise is reduced to a certain extent. For this reason the application of the technique for wind turbine immission measurements is not recommended. 11 figs., 3 tabs., 2 refs
[en] In the report the method of angular velocity determination for wind turbine of given capacity with allowing for an average seasonal wind velocity and all geometrical and dynamical characteristics of the unit is presented. It is noted, that this wind turbine has following advantages: wind direction does not plays role due to vertical axis position of the turbine; electric generator and other equipment are arranged on the ground, that reduce construction's weight, expedite of servicing and repair; the wind turbine has high coefficient of wind energy use (ξmax=0.45)