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Dr. Francesco Balduzzi
Università degli Studi di Firenze

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Research Keywords & Expertise

0 Computational Fluid Dynamics (CFD)
0 Fluid Mechanics
0 Internal Combustion Engines
0 Wind Turbines
0 Energy System Simulation

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Wind Turbines
Computational Fluid Dynamics (CFD)

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Short Biography

Francesco Balduzzi was born in Figline Valdarno, Italy on 12/05/1985. He received his master degree in Mechanical Engineering on 24/09/2009 from the University of Florence, with the thesis "3D Thermo-Fluid Dynamic Simulation of a 4 Stroke Indirect Injection Diesel Engine". On 27/07/2013, he attained the PhD in Industrial and Reliability Engineering, with the thesis "Development of a CFD approach for the performance prediction of reciprocating compressors". Currently, he is Research Fellow at the Department of Industrial Engineering of the University of Florence, and he is the technical responsible of all the numerical simulation activities of the REASE group (Reciprocating Engines and Advanced Systems for Energy) regarding fluid machines and energy systems.

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Research article
Published: 28 July 2021 in Journal of Engineering for Gas Turbines and Power
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The Actuator Line Method (ALM), combining a lumped-parameter representation of the rotating blades with the CFD resolution of the turbine flow field, stands out among the modern simulation methods for wind turbines as probably the most interesting compromise between accuracy and computational cost. Being however a method relying on tabulated coefficients for modeling the blade-flow interaction, the correct implementation of the sub-models to account for higher order aerodynamic effects is pivotal. Inter alia, the introduction of a dynamic stall model is extremely challenging: first, it is important to extrapolate a correct value of the angle of attack (AoA) from the solved flow field; second, the AoA history needed to calculate the rate of dynamic variation of the angle itself is characterized by a low signal-to-noise ratio, leading to severe numerical oscillations of the solution. The study introduces a robust procedure to improve the quality of the AoA signal extracted from an ALM simulation. It combines a novel method for sampling the inflow velocity from the numerical flow field with a low-pass filtering of the corresponding AoA signal based on Cubic Spline Smoothing. Such procedure has been implemented in the Actuator Line module developed by the authors for the commercial ANSYS® FLUENT® solver. To verify the reliability of the methodology, two-dimensional unsteady RANS simulations of a test 2-blade Darrieus H-rotor, for which high-fidelity experimental and numerical blade loading data were available, have been performed for a selected unstable operation point.

ACS Style

Pier Francesco Melani; Francesco Balduzzi; Alessandro Bianchini. A Robust Procedure to Implement Dynamic Stall Models Into Actuator Line Methods for the Simulation of Vertical-Axis Wind Turbines. Journal of Engineering for Gas Turbines and Power 2021, 1 .

AMA Style

Pier Francesco Melani, Francesco Balduzzi, Alessandro Bianchini. A Robust Procedure to Implement Dynamic Stall Models Into Actuator Line Methods for the Simulation of Vertical-Axis Wind Turbines. Journal of Engineering for Gas Turbines and Power. 2021; ():1.

Chicago/Turabian Style

Pier Francesco Melani; Francesco Balduzzi; Alessandro Bianchini. 2021. "A Robust Procedure to Implement Dynamic Stall Models Into Actuator Line Methods for the Simulation of Vertical-Axis Wind Turbines." Journal of Engineering for Gas Turbines and Power , no. : 1.

Preprint content
Published: 16 July 2021
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ACS Style

Pier Francesco Melani; Francesco Balduzzi; Pierre Alain Hoffer; Stephane Montesino; Mattia Brenner; Alessandro Bianchini; Giovanni Ferrara. Influence of Key Design Parameters on the Aerodynamic Performance of a Centrifugal Compressor Volute for Turbocharger Applications. 2021, 1 .

AMA Style

Pier Francesco Melani, Francesco Balduzzi, Pierre Alain Hoffer, Stephane Montesino, Mattia Brenner, Alessandro Bianchini, Giovanni Ferrara. Influence of Key Design Parameters on the Aerodynamic Performance of a Centrifugal Compressor Volute for Turbocharger Applications. . 2021; ():1.

Chicago/Turabian Style

Pier Francesco Melani; Francesco Balduzzi; Pierre Alain Hoffer; Stephane Montesino; Mattia Brenner; Alessandro Bianchini; Giovanni Ferrara. 2021. "Influence of Key Design Parameters on the Aerodynamic Performance of a Centrifugal Compressor Volute for Turbocharger Applications." , no. : 1.

Preprint content
Published: 16 July 2021
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ACS Style

Francesco Balduzzi; David Holst; Pier Francesco Melani; Felix Wegner; Christian Navid Nayeri; Giovanni Ferrara; Christian Oliver Paschereit; Alessandro Bianchini. Combined Numerical and Experimental Study on the Use of Gurney Flaps for the Performance Enhancement of NACA0021 Airfoil in Static and Dynamic Conditions. 2021, 1 .

AMA Style

Francesco Balduzzi, David Holst, Pier Francesco Melani, Felix Wegner, Christian Navid Nayeri, Giovanni Ferrara, Christian Oliver Paschereit, Alessandro Bianchini. Combined Numerical and Experimental Study on the Use of Gurney Flaps for the Performance Enhancement of NACA0021 Airfoil in Static and Dynamic Conditions. . 2021; ():1.

Chicago/Turabian Style

Francesco Balduzzi; David Holst; Pier Francesco Melani; Felix Wegner; Christian Navid Nayeri; Giovanni Ferrara; Christian Oliver Paschereit; Alessandro Bianchini. 2021. "Combined Numerical and Experimental Study on the Use of Gurney Flaps for the Performance Enhancement of NACA0021 Airfoil in Static and Dynamic Conditions." , no. : 1.

Journal article
Published: 18 June 2021 in Energy Conversion and Management
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Analysis tools with a fidelity higher than the ubiquitous Blade Element Momentum (BEM) method are needed by now in wind energy; in particular, different research groups have recently proposed the application of the Actuator Line Method (ALM) to wind turbines, to exploit the benefits of an accurate discretization of the wake through Computational Fluid Dynamics and the computational cost saving associated to the lumped parameter modeling of the blade. When applied to Vertical-Axis Darrieus rotors, however, several shortcomings of present models are known to the scientific community, especially regarding the spreading of aerodynamic forces in the domain and the implementation of robust aerodynamic polars and dynamic stall models. Moving from this background, an ALM method numerical model for the simulation of VAWTs has been here developed within the commercial solver ANSYS® FLUENT®. Then, in the effort of tailoring the ALM to this type of machines, different features have been implemented and discussed in the present study, including a novel strategy for the sampling of the angle of attack from the resolved flow field, a sensitivity analysis on the force spreading within the domain and numerous sub-models to account for secondary aerodynamics effects. Attention has been given at ensuring robustness to the implementation of the pivotal modeling of dynamic stall. To prove the effectiveness of proposed solutions, an extensive validation has been carried out on selected test cases, for which both high-fidelity CFD and experimental data were available: a real 2-blade H-Darrieus rotor and a fictitious 1-blade machine. The developed solutions have increased the accuracy of the predicted torque up to 16% with respect to the ALM standard formulation.

ACS Style

Pier Francesco Melani; Francesco Balduzzi; Giovanni Ferrara; Alessandro Bianchini. Tailoring the actuator line theory to the simulation of Vertical-Axis Wind Turbines. Energy Conversion and Management 2021, 243, 114422 .

AMA Style

Pier Francesco Melani, Francesco Balduzzi, Giovanni Ferrara, Alessandro Bianchini. Tailoring the actuator line theory to the simulation of Vertical-Axis Wind Turbines. Energy Conversion and Management. 2021; 243 ():114422.

Chicago/Turabian Style

Pier Francesco Melani; Francesco Balduzzi; Giovanni Ferrara; Alessandro Bianchini. 2021. "Tailoring the actuator line theory to the simulation of Vertical-Axis Wind Turbines." Energy Conversion and Management 243, no. : 114422.

Journal article
Published: 13 January 2021 in Journal of Engineering for Gas Turbines and Power
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Power augmentation devices in wind energy applications have been receiving increasing interest from both the scientific and the industrial community. In particular, Gurney flaps (GFs) showed a great potential thanks to the passive functioning, the simple construction, and the possibility to add them as a retrofit to existing rotors. Within this context, the authors have performed an extended investigation on the lift increase capabilities of GFs for the well-known NACA 0021 airfoil, which has been used in several wind energy applications up to now. This paper shows the results of a combined experimental and numerical analysis considering different geometrical configurations of the flaps under both static and dynamic conditions. Experimental data were first obtained for the AoA range of 180 degrees at a Reynolds number of 180 k to analyze the impact of three different geometrical configurations of the GF on the aerodynamic behavior. The geometrical configurations were defined by varying the length of the flap (1.4% and 2.5% of the chord) and its inclination angle with respect to the blade chord (90 deg and 45 deg). The experimental investigation involved also dynamic sinusoidal pitching movements at multiple reduced frequencies to evaluate the stall hysteresis cycle. An unsteady computational fluid dynamics (CFD) numerical model was calibrated against wind tunnel data and then exploited to extend the investigation to a wider range of Reynolds numbers for dynamic AoA rates of change typical of vertical-axis wind turbines, i.e., characterized by higher reduced frequencies with a nonsinusoidal motion law.

ACS Style

Francesco Balduzzi; David Holst; Pier Francesco Melani; Felix Wegner; Christian Navid Nayeri; Giovanni Ferrara; Christian Oliver Paschereit; Alessandro Bianchini. Combined Numerical and Experimental Study on the Use of Gurney Flaps for the Performance Enhancement of NACA0021 Airfoil in Static and Dynamic Conditions. Journal of Engineering for Gas Turbines and Power 2021, 143, 1 .

AMA Style

Francesco Balduzzi, David Holst, Pier Francesco Melani, Felix Wegner, Christian Navid Nayeri, Giovanni Ferrara, Christian Oliver Paschereit, Alessandro Bianchini. Combined Numerical and Experimental Study on the Use of Gurney Flaps for the Performance Enhancement of NACA0021 Airfoil in Static and Dynamic Conditions. Journal of Engineering for Gas Turbines and Power. 2021; 143 (2):1.

Chicago/Turabian Style

Francesco Balduzzi; David Holst; Pier Francesco Melani; Felix Wegner; Christian Navid Nayeri; Giovanni Ferrara; Christian Oliver Paschereit; Alessandro Bianchini. 2021. "Combined Numerical and Experimental Study on the Use of Gurney Flaps for the Performance Enhancement of NACA0021 Airfoil in Static and Dynamic Conditions." Journal of Engineering for Gas Turbines and Power 143, no. 2: 1.

Journal article
Published: 18 November 2020 in Renewable Energy
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Wind turbine blade erosion has risen to the attention of researchers and industry lately in an effort to keep ageing wind farms productive. Although not new, erosion-related blade damage seems to be more severe in recent, particularly off-shore, installations. With the high blade-tip speeds of modern wind turbines, installation in rainy locations can cause significant damage. While all the players in the industry agree that a reduction on Annual Energy Production (AEP) has to be expected, its magnitude remains uncertain, with wide range of variability forecasted in published research. This work proposes a probabilistic framework to assess AEP reductions, allowing for a better understanding of the key mechanism that cause turbine power loss and for a better quantification of AEP losses. The method is tested on the DTU10MW reference case. Erosion-related uncertainties are estimated based on available literature data. Lift and drag coefficients of the airfoils are derived using CFD, and the entire wind turbine is simulated aero-servo-elastically using a Blade Element Momentum code. An arbitrary Polynomial Chaos method is used to estimate the uncertainties associated to key turbine figures due to the erosion inputs. Results show how AEP reductions, while still significant, are lower than most published literature indicates.

ACS Style

Francesco Papi; Francesco Balduzzi; Giovanni Ferrara; Alessandro Bianchini. Uncertainty quantification on the effects of rain-induced erosion on annual energy production and performance of a Multi-MW wind turbine. Renewable Energy 2020, 165, 701 -715.

AMA Style

Francesco Papi, Francesco Balduzzi, Giovanni Ferrara, Alessandro Bianchini. Uncertainty quantification on the effects of rain-induced erosion on annual energy production and performance of a Multi-MW wind turbine. Renewable Energy. 2020; 165 ():701-715.

Chicago/Turabian Style

Francesco Papi; Francesco Balduzzi; Giovanni Ferrara; Alessandro Bianchini. 2020. "Uncertainty quantification on the effects of rain-induced erosion on annual energy production and performance of a Multi-MW wind turbine." Renewable Energy 165, no. : 701-715.

Journal article
Published: 22 October 2020 in Sustainability
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Tidal stream turbines fixed on the seabed can harness the power of tides at locations where the bathymetry and/or coastal geography result in high kinetic energy levels of the flood and/or neap currents. In large turbine arrays, however, avoiding interactions between upstream turbine wakes and downstream turbine rotors may be hard or impossible, and, therefore, tidal array layouts have to be designed to minimize the power losses caused by these interactions. For the first time, using Navier-Stokes computational fluid dynamics simulations which model the turbines with generalized actuator disks, two sets of flume tank experiments of an isolated turbine and arrays of up to four turbines are analyzed in a thorough and comprehensive fashion to investigate these interactions and the power losses they induce. Very good agreement of simulations and experiments is found in most cases. The key novel finding of this study is the evidence that the flow acceleration between the wakes of two adjacent turbines can be exploited not only to increase the kinetic energy available to a turbine working further downstream in the accelerated flow corridor, but also to reduce the power losses of said turbine due to its rotor interaction with the wake produced by a fourth turbine further upstream. By making use of periodic array simulations, it is also found that there exists an optimal lateral spacing of the two adjacent turbines, which maximizes the power of the downstream turbine with respect to when the two adjacent turbines are absent or further apart. This is accomplished by trading off the amount of flow acceleration between the wakes of the lateral turbines, and the losses due to shear and mixing of the front turbine wake and the wakes of the two lateral turbines.

ACS Style

Federico Attene; Francesco Balduzzi; Alessandro Bianchini; M. Sergio Campobasso. Using Experimentally Validated Navier-Stokes CFD to Minimize Tidal Stream Turbine Power Losses Due to Wake/Turbine Interactions. Sustainability 2020, 12, 8768 .

AMA Style

Federico Attene, Francesco Balduzzi, Alessandro Bianchini, M. Sergio Campobasso. Using Experimentally Validated Navier-Stokes CFD to Minimize Tidal Stream Turbine Power Losses Due to Wake/Turbine Interactions. Sustainability. 2020; 12 (21):8768.

Chicago/Turabian Style

Federico Attene; Francesco Balduzzi; Alessandro Bianchini; M. Sergio Campobasso. 2020. "Using Experimentally Validated Navier-Stokes CFD to Minimize Tidal Stream Turbine Power Losses Due to Wake/Turbine Interactions." Sustainability 12, no. 21: 8768.

Journal article
Published: 17 August 2020 in Energy Conversion and Management
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One of the key problems faced by researchers dealing with Computational Fluid Dynamics simulations and rotating machines is represented by how to extract the angle attack from a numerically computed flow field. If this issue has been addressed successfully for some applications, in case of airfoils moving in cycloidal motion (i.e. having a rotational motion within a rectilinear flow field, like in Darrieus Vertical-Axis Wind Turbines) some proposals do exist, but always affected by some arbitrary choices on the velocity probing that are not supported by a proper verification. The aim of the present study is to try finding a robust computational procedure tailored for the scope. To this end, three different post-processing methods - detailed in the study – were considered and applied to the flow fields of 2-blade H-Darrieus rotor, coming from a high-fidelity unsteady model based on Computational Fluid Dynamics; the resulting blade angle of attack trends over one rotor revolution were then combined with available blade forces data to assess the corresponding lift and drag coefficients. In order to assess the actual accuracy of these approaches for a stable tip-speed ratio, the post-processed force coefficients were compared to the ones computed via a numerical pitching airfoil model, which received the sampled angle of attack trends as input; eventually, the pitched lift and drag values have been used to reconstruct the blade forces over one rotor revolution and compare them with the ones coming from full turbine simulations. Results show large scattering of obtained data, remarking the importance of the proper selection of the angle of attack sampling strategy for the analysis of turbine performance. Overall, the “LineAverage” approach, i.e. the use of multiple sampling points around the airfoil for velocity probing, has proved to be the most accurate method.

ACS Style

Pier Francesco Melani; Francesco Balduzzi; Giovanni Ferrara; Alessandro Bianchini. How to extract the angle attack on airfoils in cycloidal motion from a flow field solved with computational fluid dynamics? Development and verification of a robust computational procedure. Energy Conversion and Management 2020, 223, 113284 .

AMA Style

Pier Francesco Melani, Francesco Balduzzi, Giovanni Ferrara, Alessandro Bianchini. How to extract the angle attack on airfoils in cycloidal motion from a flow field solved with computational fluid dynamics? Development and verification of a robust computational procedure. Energy Conversion and Management. 2020; 223 ():113284.

Chicago/Turabian Style

Pier Francesco Melani; Francesco Balduzzi; Giovanni Ferrara; Alessandro Bianchini. 2020. "How to extract the angle attack on airfoils in cycloidal motion from a flow field solved with computational fluid dynamics? Development and verification of a robust computational procedure." Energy Conversion and Management 223, no. : 113284.

Journal article
Published: 08 June 2020 in Energies
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Small Darrieus vertical-axis wind turbines (VAWTs) have recently been proposed as a possible solution for adoption in the built environment as their performance degrades less in complex and highly-turbulent flows. Some recent analyses have even shown an increase of the power coefficient for the large turbulence intensities and length scales typical of such environments. Starting from these insights, this study presents a combined numerical and experimental analysis aimed at assessing the physical phenomena that take place during the operation of a Darrieus VAWT in turbulent flows. Wind tunnel experiments provided a quantification of the performance variation of a two-blade VAWT rotor for different levels of turbulence intensity and length scale. Furthermore, detailed experiments on an individual airfoil provided an estimation of the aerodynamics at high turbulence levels and low Reynolds numbers. Computational fluid dynamics (CFD) simulations were used to extend the experimental results and to quantify the variation in the energy content of turbulent wind. Finally, the numerical and experimental inputs were synthetized into an engineering simulation tool, which can nicely predict the performance of a VAWT rotor under turbulent conditions.

ACS Style

Francesco Balduzzi; Marco Zini; Andreu Carbó Molina; Gianni Bartoli; Tim De Troyer; Mark C. Runacres; Giovanni Ferrara; Alessandro Bianchini. Understanding the Aerodynamic Behavior and Energy Conversion Capability of Small Darrieus Vertical Axis Wind Turbines in Turbulent Flows. Energies 2020, 13, 2936 .

AMA Style

Francesco Balduzzi, Marco Zini, Andreu Carbó Molina, Gianni Bartoli, Tim De Troyer, Mark C. Runacres, Giovanni Ferrara, Alessandro Bianchini. Understanding the Aerodynamic Behavior and Energy Conversion Capability of Small Darrieus Vertical Axis Wind Turbines in Turbulent Flows. Energies. 2020; 13 (11):2936.

Chicago/Turabian Style

Francesco Balduzzi; Marco Zini; Andreu Carbó Molina; Gianni Bartoli; Tim De Troyer; Mark C. Runacres; Giovanni Ferrara; Alessandro Bianchini. 2020. "Understanding the Aerodynamic Behavior and Energy Conversion Capability of Small Darrieus Vertical Axis Wind Turbines in Turbulent Flows." Energies 13, no. 11: 2936.

Journal article
Published: 03 June 2020 in Energies
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The research on two-stroke engines has been focused lately on the development of direct injection systems for reducing the emissions of hydrocarbons by minimizing the fuel short-circuiting. Low temperature combustion (LTC) may be the next step to further improve emissions and fuel consumption; however, LTC requires unconventional ignition systems. Jet ignition, i.e., the use of prechambers to accelerate the combustion process, turned out to be an effective way to perform LTC. The present work aims at proving the feasibility of adopting passive prechambers in a high-pressure, direct injection, two-stroke engine through non-reactive computational fluid dynamics analyses. The goal of the analysis is the evaluation of the prechamber performance in terms of both scavenging efficiency of burnt gases and fuel/air mixture formation inside the prechamber volume itself, in order to guarantee the mixture ignitability. Two prechamber geometries, featuring different aspect ratios and orifice numbers, were investigated. The analyses were replicated for two different locations of the injection and for three operating conditions of the engine in terms of revolution speed and load. Upon examination of the results, the effectiveness of both prechambers was found to be strongly dependent on the injection setup.

ACS Style

Marco Ciampolini; Simone Bigalli; Francesco Balduzzi; Alessandro Bianchini; Luca Romani; Giovanni Ferrara. CFD Analysis of the Fuel–Air Mixture Formation Process in Passive Prechambers for Use in a High-Pressure Direct Injection (HPDI) Two-Stroke Engine. Energies 2020, 13, 1 .

AMA Style

Marco Ciampolini, Simone Bigalli, Francesco Balduzzi, Alessandro Bianchini, Luca Romani, Giovanni Ferrara. CFD Analysis of the Fuel–Air Mixture Formation Process in Passive Prechambers for Use in a High-Pressure Direct Injection (HPDI) Two-Stroke Engine. Energies. 2020; 13 (11):1.

Chicago/Turabian Style

Marco Ciampolini; Simone Bigalli; Francesco Balduzzi; Alessandro Bianchini; Luca Romani; Giovanni Ferrara. 2020. "CFD Analysis of the Fuel–Air Mixture Formation Process in Passive Prechambers for Use in a High-Pressure Direct Injection (HPDI) Two-Stroke Engine." Energies 13, no. 11: 1.

Journal article
Published: 12 April 2020 in Energies
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The disclosing of new diffusion frontiers for wind energy, like deep-water offshore applications or installations in urban environments, is putting new focus on Darrieus vertical-axis wind turbines (VAWTs). To partially fill the efficiency gap of these turbines, aerodynamic developments are still needed. This work in particular focuses on the development of a mathematical model that allows predicting the possible performance improvements enabled in a VAWT by application of the Gurney flaps (GFs) as a function of the blade thickness, the rotor solidity and geometry of the Gurney flap itself. The performance of airfoil with GFs was evaluated by means of detailed simulations making use of computational fluid dynamics (CFD). The accuracy of the CFD model was assessed against the results of a dedicated experimental study. In the simulations, a dedicated method to simulate cycles of variation of the angle of attack similar to those taking place in a cycloidal motion (rather than purely sinusoidal ones) was also developed. Based on the results from CFD, a multidimensional interpolation based on the radial basis functions was conducted in order to find the GF design solution that provides the highest efficiency for a given turbine in terms of airfoil and solidity. The results showed that, for the selected study cases based on symmetric airfoils, the GF positioned facing outwards from the turbine, which provides the upwind part of the revolution, can lead to power increments ranging from approximately 30% for the lower-solidity turbine up to 90% for the higher-solidity turbine. It was also shown that the introduction of a GF should be coupled with a re-optimization of the airfoil thickness to maximize the performance.

ACS Style

Piotr Wiśniewski; Francesco Balduzzi; Zbigniew Buliński; Alessandro Bianchini. Numerical Analysis on the Effectiveness of Gurney Flaps as Power Augmentation Devices for Airfoils Subject to a Continuous Variation of the Angle of Attack by Use of Full and Surrogate Models. Energies 2020, 13, 1877 .

AMA Style

Piotr Wiśniewski, Francesco Balduzzi, Zbigniew Buliński, Alessandro Bianchini. Numerical Analysis on the Effectiveness of Gurney Flaps as Power Augmentation Devices for Airfoils Subject to a Continuous Variation of the Angle of Attack by Use of Full and Surrogate Models. Energies. 2020; 13 (8):1877.

Chicago/Turabian Style

Piotr Wiśniewski; Francesco Balduzzi; Zbigniew Buliński; Alessandro Bianchini. 2020. "Numerical Analysis on the Effectiveness of Gurney Flaps as Power Augmentation Devices for Airfoils Subject to a Continuous Variation of the Angle of Attack by Use of Full and Surrogate Models." Energies 13, no. 8: 1877.

Journal article
Published: 05 February 2019 in Energy Conversion and Management
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Gurney Flaps (GFs) can enhance the aerodynamic performance of airfoils, making them generate more lift and delaying the onset of stall. Since their potential was discovered in the early ‘70 s, GFs have been applied in several fields, including wind turbines. Here, the research has been focused mostly on the use of GFs in Horizontal Axis Wind Turbines (HAWTs), whereas a lack of studies involving the application of these devices on Darrieus Vertical-Axis Wind Turbines (VAWTs) is apparent in the literature. The benefits induced by GFs could actually be particularly interesting for this type of wind turbines, which are presently receiving a renewed attention from the industry. In the present work, an extended numerical analysis using Computational Fluid Dynamics (CFD) was carried out with the aim of evaluating the potential of using Gurney Flaps for the power augmentation of Darrieus wind turbines. After a validation of the numerical approach using wind tunnel experimental data on a static airfoil, the simulations have assessed the impact of different GF mounting and height on board airfoils moving in the cycloidal motion typical of Darrieus wind turbines. The results on a single rotating airfoil allowed the analysis to highlight the physical phenomena taking place past the rotating blades, including the delay of stall and the modifications induced on the surrounding flow field; power enhancements higher than 20% were shown for some configurations. Then, impact of GFs on a real three-blade turbine was analyzed. The best configuration resulted in a 2%c GF installed in the inner side of the airfoil, so to have a better torque extraction in the downwind half of the revolution. The GF benefits were apparent especially at lower tip-speed ratios, suggesting its use both for newly-designed turbines and even as a retrofitting solution in existing rotors.

ACS Style

Alessandro Bianchini; Francesco Balduzzi; Daniele Di Rosa; Giovanni Ferrara. On the use of Gurney Flaps for the aerodynamic performance augmentation of Darrieus wind turbines. Energy Conversion and Management 2019, 184, 402 -415.

AMA Style

Alessandro Bianchini, Francesco Balduzzi, Daniele Di Rosa, Giovanni Ferrara. On the use of Gurney Flaps for the aerodynamic performance augmentation of Darrieus wind turbines. Energy Conversion and Management. 2019; 184 ():402-415.

Chicago/Turabian Style

Alessandro Bianchini; Francesco Balduzzi; Daniele Di Rosa; Giovanni Ferrara. 2019. "On the use of Gurney Flaps for the aerodynamic performance augmentation of Darrieus wind turbines." Energy Conversion and Management 184, no. : 402-415.

Proceedings article
Published: 30 October 2018 in SAE Technical Paper Series
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The small two-stroke engine represents a strategic typology of propulsion system for applications in which lightweight and high power density are required. However, the conventional two-stroke engine will not be compliant with forthcoming legislations about pollutant emissions and new solutions, such as electrification, are seriously taken into account by industry to overcome the two-stroke engine drawbacks. In this scenario, a promising way to allow the two-stroke engine to be competitive is represented by the use of direct injection systems, in order to overcome the long-standing issue of short circuiting fuel. The authors in previous studies developed a low-pressure direct injection (LPDI) system for a 300 cm3 two-stroke engine that was ensuring the same power output of the engine in carbureted configuration and raw pollutant emissions consistent with a four-stroke engine of similar performance. The main drawbacks of the system were the large time required for delivering the fuel and the incomplete vaporization in some working conditions; as a result, the engine operation was limited at high revolution speed, as well as the cycle to cycle variation was amplified at very low loads. In this study, the LPDI system was replaced by a GDI system, with a single high pressure injector installed in the engine head capable of working up to an operating pressure of 150 bar. After a preliminary numerical activity to identify the best injector configuration, the system performance was evaluated at the test bench. The experiments show that the GDI system allows reaching higher revolution speeds, thanks to the shorter injection duration, with the same benefits in terms of fuel consumption reduction obtained with the LPDI technology. In-depth investigations on the injection timing and the injection pressure were carried out in order to minimize both hydrocarbon emissions and brake specific fuel consumption.

ACS Style

Luca Romani; Francesco Balduzzi; Giovanni Ferrara; Lorenzo Bosi; Rita Di Gioia; Giovanni Bonandrini; Jacopo Fiaschi; Federico Tozzi. Experimental Investigation on the Potentiality of a GDI System Applied to a Two-Stroke Engine: Analysis on Pollutant Emission and Fuel Consumption Reduction. SAE Technical Paper Series 2018, 1 .

AMA Style

Luca Romani, Francesco Balduzzi, Giovanni Ferrara, Lorenzo Bosi, Rita Di Gioia, Giovanni Bonandrini, Jacopo Fiaschi, Federico Tozzi. Experimental Investigation on the Potentiality of a GDI System Applied to a Two-Stroke Engine: Analysis on Pollutant Emission and Fuel Consumption Reduction. SAE Technical Paper Series. 2018; ():1.

Chicago/Turabian Style

Luca Romani; Francesco Balduzzi; Giovanni Ferrara; Lorenzo Bosi; Rita Di Gioia; Giovanni Bonandrini; Jacopo Fiaschi; Federico Tozzi. 2018. "Experimental Investigation on the Potentiality of a GDI System Applied to a Two-Stroke Engine: Analysis on Pollutant Emission and Fuel Consumption Reduction." SAE Technical Paper Series , no. : 1.

Proceedings article
Published: 30 October 2018 in SAE Technical Paper Series
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Modern injection systems are characterized by low cost, light weight and diversified components based on a mature technology. In addition, the constant growth of computational resources allows an in-depth understanding and control of the injection process. In this scenario, increasing interest is presently being paid to understand if an application of such technologies to small two-stroke engines could lead to a return to popularity in place of the more widespread use of the four-stroke engine. Indeed, the possibility of achieving a drastic reduction of both specific fuel consumption and pollutant emissions would completely reverse the future prospect of the two-stroke engine. The authors in previous studies developed a low pressure direct injection (LPDI) system for a 300 cm3 two-stroke engine that was ensuring a performance consistent with a standard four-stroke engine of similar size. The main drawbacks of the system were the large time required for delivering the fuel and the incomplete vaporization in some working conditions, due to the large size of the injected droplets. In this study, the use of a single high pressure injector with an operating pressure of 100 bar was analyzed. An optimization study was carried out in order to identify the best injector configuration for the GDI system. The results of the preliminary 3-D CFD study are here reported. The effect of the injector positioning and injection timing on the spray vaporization, mixture homogenization and fuel short-circuit was evaluated at different engine operating points. The results will show that also in case of a high pressure injection the best performance can be obtained when a suitable interaction between the liquid jet of fuel and the flow of scavenging air is ensured, as well as with the appropriate choice of the injection timing.

ACS Style

Francesco Balduzzi; Luca Romani; Andrea Tanganelli; Simone Bigalli; Giovanni Ferrara. On the Effect of the Injector Position on Fuel-Air Mixture Preparation in a Two-Stroke GDI Engine. SAE Technical Paper Series 2018, 1 .

AMA Style

Francesco Balduzzi, Luca Romani, Andrea Tanganelli, Simone Bigalli, Giovanni Ferrara. On the Effect of the Injector Position on Fuel-Air Mixture Preparation in a Two-Stroke GDI Engine. SAE Technical Paper Series. 2018; ():1.

Chicago/Turabian Style

Francesco Balduzzi; Luca Romani; Andrea Tanganelli; Simone Bigalli; Giovanni Ferrara. 2018. "On the Effect of the Injector Position on Fuel-Air Mixture Preparation in a Two-Stroke GDI Engine." SAE Technical Paper Series , no. : 1.

Journal article
Published: 19 September 2018 in Journal of Engineering for Gas Turbines and Power
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In centrifugal compressor design, the volute plays a key role in defining the overall efficiency and operating range of the stage. The flow at the impeller outlet is indeed characterized by a high kinetic energy content, which is first converted to potential energy in the diffuser downstream. The compressed gas is then collected by the volute at the cylindrical outlet section of the diffuser and directed to the intake piping, possibly with a further pressure recovery to enhance the stage performance. Due to the high flow speed at the volute inlet, the capability of ensuring the lowest amount of total pressure loss is pivotal to prevent a detriment of the machine efficiency. Moreover, the flow conditions change when the volute operates far from its design point: at mass flow rates lower than the design one, the flow becomes diffusive, while at higher mass flow rates the fluid is accelerated, thus leading to different loss-generation mechanisms. These phenomena are particularly relevant in turbocharger applications, where the compressor needs to cover a wide functioning range; moreover, in these applications, the definition of the volute shape is often driven also by space limitations imposed by the vehicle layout, leading to a variety of volute types. The present paper reports an analysis on the sources of thermodynamic irreversibilities occurring inside different volutes applied to a centrifugal compressor for turbocharging applications. Three demonstrative geometrical configurations are analyzed by means of three-dimensional (3D) numerical simulations using common boundary conditions to assess the overall volute performance and different loss mechanisms, which are evaluated in terms of the local entropy generation rate. The modification of the loss mechanisms in off-design conditions is also accounted for by investigating different mass flow rates. It is finally shown that the use of the entropy generation rate for the assessment of the irreversibilities is helpful to understand and localize the sources of loss in relation to the various flow structures.

ACS Style

Andrea Tanganelli; Francesco Balduzzi; Alessandro Bianchini; Francesco Cencherle; Michele De Luca; Luca Marmorini; Giovanni Ferrara. An Investigation on the Loss Generation Mechanisms Inside Different Centrifugal Compressor Volutes for Turbochargers. Journal of Engineering for Gas Turbines and Power 2018, 141, 021004 .

AMA Style

Andrea Tanganelli, Francesco Balduzzi, Alessandro Bianchini, Francesco Cencherle, Michele De Luca, Luca Marmorini, Giovanni Ferrara. An Investigation on the Loss Generation Mechanisms Inside Different Centrifugal Compressor Volutes for Turbochargers. Journal of Engineering for Gas Turbines and Power. 2018; 141 (2):021004.

Chicago/Turabian Style

Andrea Tanganelli; Francesco Balduzzi; Alessandro Bianchini; Francesco Cencherle; Michele De Luca; Luca Marmorini; Giovanni Ferrara. 2018. "An Investigation on the Loss Generation Mechanisms Inside Different Centrifugal Compressor Volutes for Turbochargers." Journal of Engineering for Gas Turbines and Power 141, no. 2: 021004.

Journal article
Published: 17 September 2018 in Journal of Engineering for Gas Turbines and Power
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To improve the efficiency of Darrieus wind turbines, which still lacks from that of horizontal-axis rotors, computational fluid dynamics (CFD) techniques are now extensively applied, since they only provide a detailed and comprehensive flow representation. Their computational cost makes them, however, still prohibitive for routine application in the industrial context, which still makes large use of low-order simulation models like the blade element momentum (BEM) theory. These models have been shown to provide relatively accurate estimations of the overall turbine performance; conversely, the description of the flow field suffers from the strong approximations introduced in the modeling of the flow physics. In this study, the effectiveness of the simplified BEM approach was critically benchmarked against a comprehensive description of the flow field past the rotating blades coming from the combination of a two-dimensional (2D) unsteady CFD model and experimental wind tunnel tests; for both data sets, the overall performance and the wake characteristics on the midplane of a small-scale H-shaped Darrieus turbine were available. Upon examination of the flow field, the validity of the ubiquitous use of induction factors is discussed, together with the resulting velocity profiles upstream and downstream the rotor. Particular attention is paid on the actual flow conditions (i.e., incidence angle and relative speed) experienced by the airfoils in motion at different azimuthal angles, for which a new procedure for the postprocessing of CFD data is here proposed. Based on this model, the actual lift and drag coefficients produced by the airfoils in motion are analyzed and discussed, with particular focus on dynamic stall. The analysis highlights the main critical issues and flaws of the low-order BEM approach, but also sheds new light on the physical reasons why the overall performance prediction of these models is often acceptable for a first-design analysis.

ACS Style

Alessandro Bianchini; Francesco Balduzzi; Giovanni Ferrara; Giacomo Persico; Vincenzo Dossena; Lorenzo Ferrari. A Critical Analysis on Low-Order Simulation Models for Darrieus Vawts: How Much Do They Pertain to the Real Flow? Journal of Engineering for Gas Turbines and Power 2018, 141, 011018 .

AMA Style

Alessandro Bianchini, Francesco Balduzzi, Giovanni Ferrara, Giacomo Persico, Vincenzo Dossena, Lorenzo Ferrari. A Critical Analysis on Low-Order Simulation Models for Darrieus Vawts: How Much Do They Pertain to the Real Flow? Journal of Engineering for Gas Turbines and Power. 2018; 141 (1):011018.

Chicago/Turabian Style

Alessandro Bianchini; Francesco Balduzzi; Giovanni Ferrara; Giacomo Persico; Vincenzo Dossena; Lorenzo Ferrari. 2018. "A Critical Analysis on Low-Order Simulation Models for Darrieus Vawts: How Much Do They Pertain to the Real Flow?" Journal of Engineering for Gas Turbines and Power 141, no. 1: 011018.

Journal article
Published: 01 August 2018 in Energy Procedia
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Thanks to the renewed interest in vertical-axis wind turbines, research efforts are devoted at improving the accuracy of present simulation tools, many of which are underdeveloped if compared to those for horizontal-axis turbines. In particular, recent studies demonstrated that a correction for the “virtual camber” effect has a major impact on the simulation. In cycloidal motion indeed the blade aerodynamics are equivalent to those of a virtually-transformed airfoil with a camber line defined by its arc of rotation. In this study, the implementation of a specific module to account for the virtual camber effect in the Open-Source code QBlade is presented. The effectiveness of the model is then validated by four 1-blade and a full 3-blade H-Darrieus turbines, for which both experimental measurements and detailed CFD calculations were available. A sensitivity analysis on the impact of the virtual camber correction on the accuracy of a low-order simulation model has been carried out as a function of the chord-to-radius ratio and the airfoil thickness-to-chord ratio. Reference thresholds for the model applicability are presented for both variables.

ACS Style

Alessandro Bianchini; David Marten; Andrea Tonini; Francesco Balduzzi; Christian Navid Nayeri; Giovanni Ferrara; Christian Oliver Paschereit. Implementation of the “Virtual Camber” Transformation into the Open Source Software QBlade: Validation and Assessment. Energy Procedia 2018, 148, 210 -217.

AMA Style

Alessandro Bianchini, David Marten, Andrea Tonini, Francesco Balduzzi, Christian Navid Nayeri, Giovanni Ferrara, Christian Oliver Paschereit. Implementation of the “Virtual Camber” Transformation into the Open Source Software QBlade: Validation and Assessment. Energy Procedia. 2018; 148 ():210-217.

Chicago/Turabian Style

Alessandro Bianchini; David Marten; Andrea Tonini; Francesco Balduzzi; Christian Navid Nayeri; Giovanni Ferrara; Christian Oliver Paschereit. 2018. "Implementation of the “Virtual Camber” Transformation into the Open Source Software QBlade: Validation and Assessment." Energy Procedia 148, no. : 210-217.

Proceedings article
Published: 11 June 2018 in Volume 8: Microturbines, Turbochargers, and Small Turbomachines; Steam Turbines
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In centrifugal compressor design, the volute plays a key role in defining the overall efficiency and operating range of the stage. The flow at the impeller outlet is indeed characterized by a high kinetic energy content, which is first converted to potential energy in the diffuser downstream. The compressed gas is then collected by the volute at the cylindrical outlet section of the diffuser and directed to the intake piping, possibly with a further pressure recovery to enhance the stage performance. Due to the high flow speed at the volute inlet, the capability of ensuring the lowest amount of total pressure loss is pivotal to prevent a detriment of the machine efficiency. Moreover, the flow conditions change when the volute operates far from its design point: at mass flow rates lower than the design one, the flow becomes diffusive, while at higher mass flow rates the fluid is accelerated, thus leading to different loss-generation mechanisms. These phenomena are particularly relevant in turbocharger applications, where the compressor needs to cover a wide functioning range; moreover, in these applications the definition of the volute shape is often driven also by space limitations imposed by the vehicle layout, leading to a variety of volute types. The present paper reports an analysis on the sources of thermodynamic irreversibilities occurring inside different volutes applied to a centrifugal compressor for turbocharging applications. Three demonstrative geometrical configurations are analyzed by means of 3D numerical simulations using common boundary conditions to assess the overall volute performance and the different loss mechanisms, which are evaluated in terms of the local entropy generation rate. The modification of the loss mechanisms in off-design conditions is also accounted for by investigating different mass flow rates. It is finally shown that the use of the entropy generation rate for the assessment of the irreversibilities is helpful to understand and localize the sources of loss in relation to the various flow structures.

ACS Style

Andrea Tanganelli; Francesco Balduzzi; Alessandro Bianchini; Giovanni Ferrara; Francesco Cencherle; Michele De Luca; Luca Marmorini. An Investigation on the Loss Generation Mechanisms Inside Different Centrifugal Compressor Volutes for Turbochargers. Volume 8: Microturbines, Turbochargers, and Small Turbomachines; Steam Turbines 2018, 1 .

AMA Style

Andrea Tanganelli, Francesco Balduzzi, Alessandro Bianchini, Giovanni Ferrara, Francesco Cencherle, Michele De Luca, Luca Marmorini. An Investigation on the Loss Generation Mechanisms Inside Different Centrifugal Compressor Volutes for Turbochargers. Volume 8: Microturbines, Turbochargers, and Small Turbomachines; Steam Turbines. 2018; ():1.

Chicago/Turabian Style

Andrea Tanganelli; Francesco Balduzzi; Alessandro Bianchini; Giovanni Ferrara; Francesco Cencherle; Michele De Luca; Luca Marmorini. 2018. "An Investigation on the Loss Generation Mechanisms Inside Different Centrifugal Compressor Volutes for Turbochargers." Volume 8: Microturbines, Turbochargers, and Small Turbomachines; Steam Turbines , no. : 1.

Proceedings article
Published: 11 June 2018 in Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy
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The wind industry needs airfoil data for ranges of Angle of Attack (AoA) much wider than those of aviation applications, since large portions of the blades may operate in stalled conditions for a significant part of their lives. Vertical axis wind turbines (VAWTs) are even more affected by this need, since data sets across the full incidence range of 180 degree are necessary for a correct performance prediction at different tip-speed ratios. However, the relevant technical literature lacks data in deep and post stall regions for nearly every airfoil. Within this context, the present study shows experimental and numerical results for the well-known NACA 0021 airfoil, which is often used for Darrieus VAWT design. Experimental data were obtained through dedicated wind tunnel measurements of a NACA 0021 airfoil with surface pressure taps, which provided further insight into the pressure coefficient distribution across a wide range of AoAs. The measurements were conducted at two different Reynolds numbers (Re = 140k and Re = 180k): each experiment was performed multiple times to ensure repeatability. Dynamic AoA changes were also investigated at multiple reduced frequencies. Moreover, dedicated unsteady numerical simulations were carried out on the same airfoil shape to reproduce both the static polars of the airfoil and some relevant dynamic AoA variation cycles tested in the experiments. The solved flow field was then exploited both to get further insight into the flow mechanisms highlighted by the wind tunnel tests and to provide correction factors to discard the influence of the experimental apparatus, making experiments representative of open-field behaviour. The present study is then thought to provide the scientific community with high quality, low-Reynolds airfoil data, which may enable in the near future a more effective design of Darrieus VAWTs.

ACS Style

Francesco Balduzzi; Alessandro Bianchini; Giovanni Ferrara; David Holst; Benjamin Church; Felix Wegner; George Pechlivanoglou; Christian Navid Nayeri; Christian Oliver Paschereit; Lorenzo Ferrari. Static and Dynamic Analysis of a NACA 0021 Airfoil Section at Low Reynolds Numbers Based on Experiments and CFD. Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy 2018, 1 .

AMA Style

Francesco Balduzzi, Alessandro Bianchini, Giovanni Ferrara, David Holst, Benjamin Church, Felix Wegner, George Pechlivanoglou, Christian Navid Nayeri, Christian Oliver Paschereit, Lorenzo Ferrari. Static and Dynamic Analysis of a NACA 0021 Airfoil Section at Low Reynolds Numbers Based on Experiments and CFD. Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy. 2018; ():1.

Chicago/Turabian Style

Francesco Balduzzi; Alessandro Bianchini; Giovanni Ferrara; David Holst; Benjamin Church; Felix Wegner; George Pechlivanoglou; Christian Navid Nayeri; Christian Oliver Paschereit; Lorenzo Ferrari. 2018. "Static and Dynamic Analysis of a NACA 0021 Airfoil Section at Low Reynolds Numbers Based on Experiments and CFD." Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy , no. : 1.

Proceedings article
Published: 11 June 2018 in Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy
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To improve the efficiency of Darrieus wind turbines, which still lacks from that of horizontal-axis rotors, Computational Fluid Dynamics (CFD) techniques are now extensively applied, since they only provide a detailed and comprehensive flow representation. Their computational cost makes them, however, still prohibitive for routine application in the industrial context, which still makes large use of low-order simulation models like the Blade Element Momentum (BEM) theory. These models have been shown to provide relatively accurate estimations of the overall turbine performance; conversely, the description of the flow field suffers from the strong approximations introduced in the modelling of the flow physics. In the present study, the effectiveness of the simplified BEM approach was critically benchmarked against a comprehensive description of the flow field past the rotating blades coming from the combination of a two-dimensional unsteady CFD model and experimental wind tunnel tests; for both data sets, the overall performance and the wake characteristics on the mid plane of a small-scale H-shaped Darrieus turbine were available. Upon examination of the flow field, the validity of the ubiquitous use of induction factors is discussed, together with the resulting velocity profiles upstream and downstream the rotor. Particular attention is paid on the actual flow conditions (i.e. incidence angle and relative speed) experienced by the airfoils in motion at different azimuthal angles, for which a new procedure for the post-processing of CFD data is here proposed. Based on this model, the actual lift and drag coefficients produced by the airfoils in motion are analyzed and discussed, with particular focus on dynamic stall. The analysis highlights the main critical issues and flaws of the low-order BEM approach, but also sheds new light on the physical reasons why the overall performance prediction of these models is often acceptable for a first-design analysis.

ACS Style

Alessandro Bianchini; Francesco Balduzzi; Giovanni Ferrara; Giacomo Persico; Vincenzo Dossena; Lorenzo Ferrari. A Critical Analysis on Low-Order Simulation Models for Darrieus VAWTs: How Much Do They Pertain to the Real Flow? Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy 2018, 1 .

AMA Style

Alessandro Bianchini, Francesco Balduzzi, Giovanni Ferrara, Giacomo Persico, Vincenzo Dossena, Lorenzo Ferrari. A Critical Analysis on Low-Order Simulation Models for Darrieus VAWTs: How Much Do They Pertain to the Real Flow? Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy. 2018; ():1.

Chicago/Turabian Style

Alessandro Bianchini; Francesco Balduzzi; Giovanni Ferrara; Giacomo Persico; Vincenzo Dossena; Lorenzo Ferrari. 2018. "A Critical Analysis on Low-Order Simulation Models for Darrieus VAWTs: How Much Do They Pertain to the Real Flow?" Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy , no. : 1.