A. Brighenti

Analysis of Different Blade Architectures on small VAWT Performance

The present paper aims at describing and comparing different small Vertical Axis Wind Turbine (VAWT) architectures, in terms of performance and loads. These characteristics can be highlighted by resorting to the Blade Element-Momentum (BE-M) model, commonly adopted for rotor pre-design and controller assessment. After validating the model with experimental data, the paper focuses on the analysis of VAWT loads depending on some relevant rotor features: blade number (2 and 3), airfoil camber line (comparing symmetrical and asymmetrical profiles) and blade inclination (straight versus helical blade). The effect of such characteristics on both power and thrusts (in the streamwise direction and in the crosswise one) as a function of both the blades azimuthal position and their Tip Speed Ratio (TSR) are presented and widely discussed.

Reliability of numerical wind tunnels for VAWT simulation

Computational Fluid Dynamics (CFD) based on the Unsteady Reynolds Averaged Navier Stokes (URANS) equations have long been widely used to study vertical axis wind turbines (VAWTs). Following a comprehensive experimental survey on the wakes downwind of a troposkien-shaped rotor, a campaign of bi-dimensional simulations is presented here, with the aim of assessing its reliability in reproducing the main features of the flow, also identifying areas needing additional research. Starting from both a well consolidated turbulence model (k-ω SST) and an unstructured grid typology, the main simulation settings are here manipulated in a convenient form to tackle rotating grids reproducing a VAWT operating in an open jet wind tunnel. The dependence of the numerical predictions from the selected grid spacing is investigated, thus establishing the less refined grid size that is still capable of capturing some relevant flow features such as integral quantities (rotor torque) and local ones (wake velocities).

Normalized performance and load data for the deepwind demonstrator in controlled conditions

Performance and load normalized coefficients, deriving from an experimental campaign of measurements conducted at the large scale wind tunnel of the Politecnico di Milano (Italy), are presented with the aim of providing useful benchmark data for the validation of numerical codes. Rough data, derived from real scale measurements on a three-bladed Troposkien vertical-axis wind turbine, are manipulated in a convenient form to be easily compared with the typical outputs provided by simulation codes. The here proposed data complement and support the measurements already presented in “Wind Tunnel Testing of the DeepWind Demonstrator in Design and Tilted Operating Conditions” (Battisti et al., 2016) [1].

Performance and midspan wake measurements on a H-Darrieus in controlled conditions

Performance and wake measurements on a H-Darrieus vertical axis wind turbine are discussed on the basis of an extensive experimental campaign performed at the large scale, high speed wind tunnel of the Politecnico di Milano (IT). The paper proposes a combined mechanical and fluid-dynamic investigation by virtue of an advanced measurement system that allows to reconstruct both phase-resolved thrust and torque acting on the machine and the phase-resolved multi-dimensional velocity field in the wake. The aerodynamic torque is presented as a function of the azimuthal angle of revolution, while the velocity field in the wake is fully characterized by means of a point to point detailed measurement on the midspan plane, where the influence of both blade support struts and tip vortices is negligible. Particular care is taken in the description of the experimental setup as well as in the presentation of the measurements. The here proposed achievements can be considered as a benchmark for the validation of several classes of computational tools.

A Review Based on Evaluation Experiences with Ten-Years Activity in VAWT Experimental Wind Tunnel Testing

The purpose of this paper is to provide guidance on the practice gained on vertical-axis wind turbine (VAWT) testing by a combined group of researchers from the Universita di Trento (IT) and the Politecnico di Milano (IT), from early experiences dating back to 2007 up to the present day. The adopted operating procedures are discussed with particular care set to the achievement of high precision measurements to be used both as a benchmark for the validation of numerical codes and as a contribution to a deeper understanding of the flow field around VAWTs, to be converted into novel measurement procedures. As a matter of fact, by providing historical and technical information from the ongoing research activity, the lessons learned about the main obtained results could serve as a valuable tool for use by other research groups who are facing similar activities, providing information on which to help base their project plans.

An Experimental Study of the Aerodynamics and Performance of a Vertical Axis Wind Turbine in Confined and Non-Confined Environment

This paper presents the results of a wide experimental study on an H-type Vertical Axis Wind Turbine (VAWT) carried out at Politecnico di Milano in the frame of the national founded project PRIN 2009. The experiments were carried out in the large-scale wind tunnel of the Politecnico di Milano, where real-scale wind turbines for micro generation can be tested in full similarity conditions. Integral torque and thrust measurements were performed, as well as detailed aerodynamic measurements to characterize the flow field generated by the turbine downstream of the rotor.The machine was tested in both confined and non-confined environment, to highlight the effect of wind tunnel blockage on the aerodynamics and performance of the VAWT under investigation. The experimental results, compared with the blockage correlations presently available, suggest that specific correction models should be developed for VAWTs. The experimental thrust and power curves of the turbine, derived from integral measurements, exhibit the expected trends with a peak power coefficient of about 0.28 at tip-speed ratio λ = 2.5. Detailed flow measurements, performed in three conditions for λ equal to 1.5, 2.5 and 3.5, show the fully three-dimensional character of the wake, especially in the tip region where a non-symmetrical wake and tip vortex are found. The unsteady evolution of the velocity and turbulence fields further highlight the effect of aerodynamic loading on the wake unsteadiness, showing the time-dependent nature of the tip vortex and the onset of a non-symmetric dynamic stall for λ lower than 2.Copyright