Alberto Santolin | Università degli Studi di Padova (original) (raw)

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Papers by Alberto Santolin

Research paper thumbnail of Procedure per la progettazione standardizzata delle turbine delle piccole centrali idroelettriche

Research paper thumbnail of Variable-speed Pelton turbine for an efficient exploitation of the reserved flow: an Italian case study

This paper presents an Italian case study of a small hydropower plant exploiting the reserved flo... more This paper presents an Italian case study of a small hydropower plant exploiting the reserved flow (RF) at the dam outlet. The significant variations of the water level in the reservoir and of the seasonal RF discharged in accordance with the Italian environmental laws determine extremely variable operating conditions for the hydropower plant that can be efficiently faced only resorting to a variable speed turbine. This breakthrough technology allows to optimize the machine performance at a wider range of operating conditions, but still presents several issues to be faced, for example the lack of standardized design criteria. This study was focused on the design optimization of the variable-speed Pelton turbine to be installed in the small hydropower plant. Numerical analyses were carried out by the commercial code Ansys CFX 14 to define a Pelton bucket geometry characterized by high efficiency values in the requested wide operating range. , A transient homogeneous model coupled with a SST turbulence model was applied to solve the two-phase flow field., Experimental analyses were also carried out on the optimized runner in an open water test rig of the Laboratory of Turbomachinery of the University of Padova to validate the numerical simulations results. The experimental test rig, equipped with a pressurized reservoir, was properly settled so as to verify the turbine performance in a wide operating range. Finally, the results of the combined numerical and experimental design optimization were verified by comparison with the performance of the model installed in the small hydropower plant of Forte Buso.

Research paper thumbnail of Using splitter blades to improve suction performance of centrifugal impeller pumps

Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2014

ABSTRACT A comparison between centrifugal impeller pumps with and without splitter blades in term... more ABSTRACT A comparison between centrifugal impeller pumps with and without splitter blades in terms of suction performance is presented by experimental tests and numerical analyses. The design of both pumps was carried out by preserving the impeller meridional shape, number of blades, and volute casing. Blade shapes were obtained by adopting a 1D inverse design method. The same blade loading distribution was assumed for the full blades of both impellers, while the loading distribution of the splitter blades was modified until a close matching between the two head-capacity curves was achieved. The fulfilment of this performance requirement and the use of the same number of blades were needed to describe accurately the role played by the splitter blades in cavitation inception and development. Differently from other experimental comparisons, where previous requirements were not met, a noticeable improvement in suction performance was found at large flow rates but not at partial ones, where a small deterioration in suction performance was observed. The crucial role played by the blade thickness blockage on the incidence flow angle at the leading edge of the full blades was also investigated.

Research paper thumbnail of Influence of the bucket geometry on the Pelton performance

Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2014

The increasing share of hydropower in world electricity production requires the development of st... more The increasing share of hydropower in world electricity production requires the development of standardized and optimized design procedures leading to increasingly higher efficiency values. To date, despite a certain amount of support from computational fluid dynamics, Pelton turbines are still characterized by semiempirical design criteria that do not make it possible to optimize the jet-bucket interaction in order to maximize turbine performance. Based on an analysis of particle flow tracks, this paper presents a hybrid Eulerian-Lagrangian method to investigate the influence of bucket geometry on the Pelton efficiency at two different operating conditions. Jet-bucket interaction was numerically analyzed by means of a traditional mesh-based numerical approach, using a transient multi-phase homogeneous model. Subsequently, the numerical results were integrated using a predictorcorrector algorithm, combining a fourth order Adams-Bashforth method as predictor and a fourth order Adams-Moulton method as corrector, in order to determine the fluid particle trajectories on the rotating buckets. The particle flow tracks were analyzed in detail to evaluate the single-particle performance in terms of discharged kinetic energy, momentum variation, and total energy variation during the jet-bucket interaction. Moreover, on the basis of the particle discharging position, the contribution of the different bucket areas to the total torque of the turbine was investigated to determine the time-depending influence of the bucket geometry on the turbine energy exchange and to suggest possible design solutions for improving bucket performance.

Research paper thumbnail of Numerical Analyses of Cavitating Flow in a Pelton Turbine

Journal of Fluids Engineering, 2014

ABSTRACT Erosion and wear of hydraulic surfaces are frequent problems in hydraulic turbines, whic... more ABSTRACT Erosion and wear of hydraulic surfaces are frequent problems in hydraulic turbines, which lead to a decrease of the performance in time and/or in extreme cases to the rotor mechanical failure. These circumstances have negative repercussions on the annual produced power due to the decay of the efficiency, the delivered power, and to the off line periods as result of ordinary and extraordinary hydraulic profiles maintenances. Consistently, the study of this wearing process is an important step to improve the impeller design, and to avoid or minimize the rise of extraordinary maintenance. While mechanical damages are well documented and studied, little information can be found on cavitation in Pelton turbines. In this paper, a CFD model was applied to study the cavitation mechanics on a Pelton turbine. A Pelton runner affected by pitting cavitation was taken as a test case. The bucket geometry was modeled and analyzed using unsteady Reynolds averaged Navier-Stokes (RANS) multiphase analyses. Numerical results allowed us to highlight the different vapor productions during the cut-in water jet processes by the bucket. Furthermore, a simple procedure to identify the locations of higher damage risk was presented and verified in the test case runner

Research paper thumbnail of Techno-economical method for the capacity sizing of a small hydropower plant

Energy Conversion and Management, 2011

ABSTRACT This paper presents a method for the capacity sizing of a small hydropower plant on the ... more ABSTRACT This paper presents a method for the capacity sizing of a small hydropower plant on the basis of techno-economical analyses of the flow duration curve. Seven technical and economical parameters were considered: the turbine type, the turbine dimensions, the annual energy production, the maximum installation height to avoid cavitation inception, the machine cost, the Net Present Value (NPV) and the Internal Rate of Return (IRR).A proper model was proposed to study the effects of the design operating conditions on these parameters. The model, applied to the flow duration curve, allowed to analyse the feasibility, the profitability and the performance of the plant in the available flowing range of the site.To verify the effectiveness of the proposed method, three sites having different flow duration curves were analysed.

Research paper thumbnail of Numerical investigation of the interaction between jet and bucket in a Pelton turbine

Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2009

... Lucia Sileo, Sverre Steen ... In 2007 MARINTEK (Norwegian Marine Technology Re-search Institu... more ... Lucia Sileo, Sverre Steen ... In 2007 MARINTEK (Norwegian Marine Technology Re-search Institute) carried out an extensive series of model tests on an offshore vessel model as a part of the University Technology Center research by Rolls-Royce Marine. ...

Research paper thumbnail of Procedure per la progettazione standardizzata delle turbine delle piccole centrali idroelettriche

Research paper thumbnail of Variable-speed Pelton turbine for an efficient exploitation of the reserved flow: an Italian case study

This paper presents an Italian case study of a small hydropower plant exploiting the reserved flo... more This paper presents an Italian case study of a small hydropower plant exploiting the reserved flow (RF) at the dam outlet. The significant variations of the water level in the reservoir and of the seasonal RF discharged in accordance with the Italian environmental laws determine extremely variable operating conditions for the hydropower plant that can be efficiently faced only resorting to a variable speed turbine. This breakthrough technology allows to optimize the machine performance at a wider range of operating conditions, but still presents several issues to be faced, for example the lack of standardized design criteria. This study was focused on the design optimization of the variable-speed Pelton turbine to be installed in the small hydropower plant. Numerical analyses were carried out by the commercial code Ansys CFX 14 to define a Pelton bucket geometry characterized by high efficiency values in the requested wide operating range. , A transient homogeneous model coupled with a SST turbulence model was applied to solve the two-phase flow field., Experimental analyses were also carried out on the optimized runner in an open water test rig of the Laboratory of Turbomachinery of the University of Padova to validate the numerical simulations results. The experimental test rig, equipped with a pressurized reservoir, was properly settled so as to verify the turbine performance in a wide operating range. Finally, the results of the combined numerical and experimental design optimization were verified by comparison with the performance of the model installed in the small hydropower plant of Forte Buso.

Research paper thumbnail of Using splitter blades to improve suction performance of centrifugal impeller pumps

Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2014

ABSTRACT A comparison between centrifugal impeller pumps with and without splitter blades in term... more ABSTRACT A comparison between centrifugal impeller pumps with and without splitter blades in terms of suction performance is presented by experimental tests and numerical analyses. The design of both pumps was carried out by preserving the impeller meridional shape, number of blades, and volute casing. Blade shapes were obtained by adopting a 1D inverse design method. The same blade loading distribution was assumed for the full blades of both impellers, while the loading distribution of the splitter blades was modified until a close matching between the two head-capacity curves was achieved. The fulfilment of this performance requirement and the use of the same number of blades were needed to describe accurately the role played by the splitter blades in cavitation inception and development. Differently from other experimental comparisons, where previous requirements were not met, a noticeable improvement in suction performance was found at large flow rates but not at partial ones, where a small deterioration in suction performance was observed. The crucial role played by the blade thickness blockage on the incidence flow angle at the leading edge of the full blades was also investigated.

Research paper thumbnail of Influence of the bucket geometry on the Pelton performance

Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2014

The increasing share of hydropower in world electricity production requires the development of st... more The increasing share of hydropower in world electricity production requires the development of standardized and optimized design procedures leading to increasingly higher efficiency values. To date, despite a certain amount of support from computational fluid dynamics, Pelton turbines are still characterized by semiempirical design criteria that do not make it possible to optimize the jet-bucket interaction in order to maximize turbine performance. Based on an analysis of particle flow tracks, this paper presents a hybrid Eulerian-Lagrangian method to investigate the influence of bucket geometry on the Pelton efficiency at two different operating conditions. Jet-bucket interaction was numerically analyzed by means of a traditional mesh-based numerical approach, using a transient multi-phase homogeneous model. Subsequently, the numerical results were integrated using a predictorcorrector algorithm, combining a fourth order Adams-Bashforth method as predictor and a fourth order Adams-Moulton method as corrector, in order to determine the fluid particle trajectories on the rotating buckets. The particle flow tracks were analyzed in detail to evaluate the single-particle performance in terms of discharged kinetic energy, momentum variation, and total energy variation during the jet-bucket interaction. Moreover, on the basis of the particle discharging position, the contribution of the different bucket areas to the total torque of the turbine was investigated to determine the time-depending influence of the bucket geometry on the turbine energy exchange and to suggest possible design solutions for improving bucket performance.

Research paper thumbnail of Numerical Analyses of Cavitating Flow in a Pelton Turbine

Journal of Fluids Engineering, 2014

ABSTRACT Erosion and wear of hydraulic surfaces are frequent problems in hydraulic turbines, whic... more ABSTRACT Erosion and wear of hydraulic surfaces are frequent problems in hydraulic turbines, which lead to a decrease of the performance in time and/or in extreme cases to the rotor mechanical failure. These circumstances have negative repercussions on the annual produced power due to the decay of the efficiency, the delivered power, and to the off line periods as result of ordinary and extraordinary hydraulic profiles maintenances. Consistently, the study of this wearing process is an important step to improve the impeller design, and to avoid or minimize the rise of extraordinary maintenance. While mechanical damages are well documented and studied, little information can be found on cavitation in Pelton turbines. In this paper, a CFD model was applied to study the cavitation mechanics on a Pelton turbine. A Pelton runner affected by pitting cavitation was taken as a test case. The bucket geometry was modeled and analyzed using unsteady Reynolds averaged Navier-Stokes (RANS) multiphase analyses. Numerical results allowed us to highlight the different vapor productions during the cut-in water jet processes by the bucket. Furthermore, a simple procedure to identify the locations of higher damage risk was presented and verified in the test case runner

Research paper thumbnail of Techno-economical method for the capacity sizing of a small hydropower plant

Energy Conversion and Management, 2011

ABSTRACT This paper presents a method for the capacity sizing of a small hydropower plant on the ... more ABSTRACT This paper presents a method for the capacity sizing of a small hydropower plant on the basis of techno-economical analyses of the flow duration curve. Seven technical and economical parameters were considered: the turbine type, the turbine dimensions, the annual energy production, the maximum installation height to avoid cavitation inception, the machine cost, the Net Present Value (NPV) and the Internal Rate of Return (IRR).A proper model was proposed to study the effects of the design operating conditions on these parameters. The model, applied to the flow duration curve, allowed to analyse the feasibility, the profitability and the performance of the plant in the available flowing range of the site.To verify the effectiveness of the proposed method, three sites having different flow duration curves were analysed.

Research paper thumbnail of Numerical investigation of the interaction between jet and bucket in a Pelton turbine

Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2009

... Lucia Sileo, Sverre Steen ... In 2007 MARINTEK (Norwegian Marine Technology Re-search Institu... more ... Lucia Sileo, Sverre Steen ... In 2007 MARINTEK (Norwegian Marine Technology Re-search Institute) carried out an extensive series of model tests on an offshore vessel model as a part of the University Technology Center research by Rolls-Royce Marine. ...