2023
Zanetti, Giacomo; Cavazzini, Giovanna; Santolin, Alberto
Three-dimensional evolution of the flow unsteadiness in the S-shape of pump-turbines and its correlation with the runner geometry Journal Article
In: Journal of Energy Storage, vol. 57, iss. September 2022, pp. 106176, 2023, ISSN: 2352152X.
Abstract | Links | BibTeX | Tags: Interblade vortex, Pump as Turbine, Pumped-hydropower, Rotating Stall, S-shape
@article{Zanetti2023,
title = {Three-dimensional evolution of the flow unsteadiness in the S-shape of pump-turbines and its correlation with the runner geometry},
author = {Giacomo Zanetti and Giovanna Cavazzini and Alberto Santolin},
url = {https://doi.org/10.1016/j.est.2022.106176},
doi = {10.1016/j.est.2022.106176},
issn = {2352152X},
year = {2023},
date = {2023-01-01},
journal = {Journal of Energy Storage},
volume = {57},
issue = {September 2022},
pages = {106176},
publisher = {Elsevier Ltd},
abstract = {Pump-turbines (RTP) are the most common mechanical equipment adopted in pumped-hydro power plants and, for grid balancing purposes, are required to sharply switch from pumping to generating mode, and to extend their operative, jeopardizing not only the machine operability but also its life. New design approaches to avoid the onset of unstable behaviours are still far from being defined, and control strategies for accelerating start-up/shut-down procedures are still not effective since these are based on semi-empirical approaches, due to the lack of identification of precursors of the unstable behavior. In this paper, a numerical analysis of the unstable behavior of an RPT during the transition from partial load up to the turbine-brake area was carried out. The fluid-dynamics in different operating points (partial load, run-away condition, turbine brake) was deeply investigated, identifying the rotor-stator mechanisms causing the 3D evolution of the flow field leading to the development of the unstable behavior. Three evolution phases (inception, growth and consolidation) were identified and clearly correlated with the runner geometry and with the S-Shape of the RPT characteristic curve. Customized signal processing strategies were adopted for spectrally characterizing each phase so as to identify potential triggers for new monitoring and control strategies. Moreover, for the first time, a clear fluid-dynamic explanation of the empirical results found in literature on the influence of the runner geometry is provided.},
keywords = {Interblade vortex, Pump as Turbine, Pumped-hydropower, Rotating Stall, S-shape},
pubstate = {published},
tppubtype = {article}
}
Pump-turbines (RTP) are the most common mechanical equipment adopted in pumped-hydro power plants and, for grid balancing purposes, are required to sharply switch from pumping to generating mode, and to extend their operative, jeopardizing not only the machine operability but also its life. New design approaches to avoid the onset of unstable behaviours are still far from being defined, and control strategies for accelerating start-up/shut-down procedures are still not effective since these are based on semi-empirical approaches, due to the lack of identification of precursors of the unstable behavior. In this paper, a numerical analysis of the unstable behavior of an RPT during the transition from partial load up to the turbine-brake area was carried out. The fluid-dynamics in different operating points (partial load, run-away condition, turbine brake) was deeply investigated, identifying the rotor-stator mechanisms causing the 3D evolution of the flow field leading to the development of the unstable behavior. Three evolution phases (inception, growth and consolidation) were identified and clearly correlated with the runner geometry and with the S-Shape of the RPT characteristic curve. Customized signal processing strategies were adopted for spectrally characterizing each phase so as to identify potential triggers for new monitoring and control strategies. Moreover, for the first time, a clear fluid-dynamic explanation of the empirical results found in literature on the influence of the runner geometry is provided.
2018
Cavazzini, Giovanna; Houdeline, Jean-Bernard Bernard; Pavesi, Giorgio; Teller, Olivier; Ardizzon, Guido
Unstable behaviour of pump-turbines and its effects on power regulation capacity of pumped-hydro energy storage plants Journal Article
In: Renewable and Sustainable Energy Reviews, vol. 94, iss. April 2017, pp. 399-409, 2018, ISSN: 18790690.
Abstract | Links | BibTeX | Tags: Hump zone, Pump as Turbine, Pumped-hydro, S-shape, Storage, Unstable behaviour
@article{Cavazzini2018,
title = {Unstable behaviour of pump-turbines and its effects on power regulation capacity of pumped-hydro energy storage plants},
author = {Giovanna Cavazzini and Jean-Bernard Bernard Houdeline and Giorgio Pavesi and Olivier Teller and Guido Ardizzon},
url = {https://doi.org/10.1016/j.rser.2018.06.018 https://linkinghub.elsevier.com/retrieve/pii/S1364032118304532},
doi = {10.1016/j.rser.2018.06.018},
issn = {18790690},
year = {2018},
date = {2018-01-01},
journal = {Renewable and Sustainable Energy Reviews},
volume = {94},
issue = {April 2017},
pages = {399-409},
publisher = {Elsevier Ltd},
abstract = {Intermittent renewable energy sources are characterized by a highly fluctuating, unpredictable and delocalized energy production, which significantly limits their penetration in the grid due to the great problems caused in the balance between demand and supply. Pumped Hydro Energy Storage plants represent an ideal solution because of their ability to provide large storage capacity with excellent grid connection properties, high cycle efficiency range and competitive costs. However, to provide primary and secondary regulation services, PHES have to increase their operation at part loads and to be able to switch fast and frequently between pump and turbine modes. At these operating conditions, pump-turbines suffer from behaviour instabilities, thereby constituting a limit when considering their exploitation in a wider continuous working range. So, the definition of a new concept of pump-turbines able to provide the full benefit of regulation in pumping mode and a wide range of power in generation mode is an urgent need to increase the exploitation of renewable energy sources. This paper clarifies the effects of the stable and unstable behaviour of pump-turbines on the power regulation capacity of pumped hydro energy storage plants, by presenting a description of the possible operating modes of PHES and by focusing on the impact of the hydraulic characteristics of pump-turbines on the capability of plant to start-up, shut-down or change its operating modes. A detailed review of the studies published in literature on the topic revealed the main characteristics of the hydraulic instabilities and the influence of one or more geometrical parameters on their onset. Even though some geometry modifications aimed at improving the RPT's stability in one operating mode were proposed in literature, the definition of a comprehensive design strategy, globally optimizing the pump-turbine design by considering simultaneously the complexity of the phenomena in both the operating modes, still represents a challenge.},
keywords = {Hump zone, Pump as Turbine, Pumped-hydro, S-shape, Storage, Unstable behaviour},
pubstate = {published},
tppubtype = {article}
}
Intermittent renewable energy sources are characterized by a highly fluctuating, unpredictable and delocalized energy production, which significantly limits their penetration in the grid due to the great problems caused in the balance between demand and supply. Pumped Hydro Energy Storage plants represent an ideal solution because of their ability to provide large storage capacity with excellent grid connection properties, high cycle efficiency range and competitive costs. However, to provide primary and secondary regulation services, PHES have to increase their operation at part loads and to be able to switch fast and frequently between pump and turbine modes. At these operating conditions, pump-turbines suffer from behaviour instabilities, thereby constituting a limit when considering their exploitation in a wider continuous working range. So, the definition of a new concept of pump-turbines able to provide the full benefit of regulation in pumping mode and a wide range of power in generation mode is an urgent need to increase the exploitation of renewable energy sources. This paper clarifies the effects of the stable and unstable behaviour of pump-turbines on the power regulation capacity of pumped hydro energy storage plants, by presenting a description of the possible operating modes of PHES and by focusing on the impact of the hydraulic characteristics of pump-turbines on the capability of plant to start-up, shut-down or change its operating modes. A detailed review of the studies published in literature on the topic revealed the main characteristics of the hydraulic instabilities and the influence of one or more geometrical parameters on their onset. Even though some geometry modifications aimed at improving the RPT's stability in one operating mode were proposed in literature, the definition of a comprehensive design strategy, globally optimizing the pump-turbine design by considering simultaneously the complexity of the phenomena in both the operating modes, still represents a challenge.
