PROGRAMMA PRIN 2022 - BANDO PRIN2022 D.D. N.104 DEL 2 FEBBRAIO 2022
TITOLO DEL PROGETTO: Diffuser augmented Wind Turbines for URBban environments (DWTURB)
CODICE CUP : D53D23003300006
Budget: € 129.385
P.I. : Prof.ssa Stefania Cherubini
Altre Unità di Ricerca o eventuali Sub Unità: Università degli Studi di Napoli Federico II
Description of the project
The project DWTURB has aimed at developing an accurate numerical modeling of Diffuser Augmented Wind Turbines (DAWTs), which consist of a wind turbine rotor installed inside an annular wing. The benefit of these turbines relies on the possibility of extracting more power from the wind compared to an Open Wind Turbine (OWT) with the same frontal area, due to the extra mass flow that a DAWT can swallow thanks to the fruitful synergy between duct and rotor. This allows a considerable energy production even at low cut-in wind speeds, and lowers the noise. The performance of DAWTs is generally analysed using theoretical or numerical approaches modeling the rotor as an actuator disk (AD), which renders the simulations computationally cheap, but does not account for the presence of a finite number of blades and for the boundary layer separation that may occur on the diffuser area.
Aim of the project
The present project has aimed at carrying out Reynolds-Averaged Navier-Stokes Simulations (RANS) and Large Eddy Simulations (LES) for ensuring an accurate modeling and estimate of the performances of these turbines.
Expected results
The activity went beyond the mere selection of a previously adopted DAWT configuration and were expected to evolve into a structured aerodynamic design that overcomes the classical uncoupled approach commonly adopted in the literature, where the rotor and the diffuser are designed separately. Starting from a reference geometry, a systematic CFD-based design strategy was expected to be developed to investigate the coupled interaction between rotor and diffuser and to identify the key geometric and operational parameters governing power extraction enhancement.
Achieved results
Three-dimensional RANS simulations were then carried out to provide detailed insight into the flow field, pressure distribution, and rotor–duct interaction mechanisms. Particular attention was devoted to ensuring the robustness of the numerical framework, which was further supported by validation activities performed on an additional wind turbine configuration for which experimental data were available. Large Eddy Simulations are then carried out, in order to compare the aerodynamic performance and flow characteristics of the considered ducted turbine and a conventional open wind turbine. The operational effects on performance of partial-load maximum power point tracking and the impact of geometrical variations of the diffuser, particularly in the divergent section downstream of the rotor, on the wake dynamics and power output, are evaluated. As demonstrated by the simulations, the implementation of a diffuser has been shown to enhance the flow ingested by the rotor. This, in turn, has been found to result in increased generation of power in comparison with an open configuration. With the aim of developing dynamically accurate Reduced-Order Models (ROM) of such a complex flow, the flow fields obtained by Large Eddy Simulations have been then used as a database for modal decompositions. On these three-dimensional flow fields, the Dynamic Mode Decompositon is applied, allowing a cheap flow reconstruction capable of estimating the performance and impact of wind turbines on the environment with acceptable accuracy and low computational cost. Additional efforts were devoted to the development of computationally efficient modelling tools capable of retaining the essential physics of rotor–diffuser interaction. The proposed framework consistently integrates local aerodynamic loading and global flow response within a reduced computational setting, preserving the key interaction mechanisms responsible for performance enhancement. This approach enabled the development of a physically grounded and efficient predictive tool for DAWT performance analysis, aligned with the overall objective of providing reliable methodologies for design and optimization with substantially reduced computational cost.