Abstract
Abstract. Multi-element ducts are used to improve the aerodynamic performance of ducted wind turbines (DWTs). Steady-state, two-dimensional computational fluid dynamics (CFD) simulations are performed for a multi-element duct geometry consisting of a duct and a flap; the goal is to evaluate the effects on the aerodynamic performance of the radial gap length and the deflection angle of the flap. Solutions from inviscid and viscous flow calculations are compared. It is found that increasing the radial gap length results in an augmentation of the total thrust generated by the DWT, whereas a larger deflection angle has an opposite effect. Reasonable to good agreement is seen between the inviscid and viscous flow calculations, except for multi-element duct configurations characterized by large flap deflection angles. The viscous effects become stronger at large flap deflection angles, and the inviscid calculations are incapable of taking this phenomenon into account.
Highlights
Ducted wind turbines (DWTs) represent an interesting technological solution for increasing energy extraction with respect to conventional horizontal-axis wind turbines (HAWTs) for a given rotor radius and free-stream velocity (de Vries, 1979)
DWTs consist of a rotor and a duct; the role of the latter is to increase the mass flow rate through the rotor relative to a similar rotor operating in the open atmosphere, thereby increasing the generated power
A positive value of radial gap (ζ > 0) indicates that the leading edge of the flap is positioned below the trailing edge of the duct
Summary
Ducted wind turbines (DWTs) represent an interesting technological solution for increasing energy extraction with respect to conventional horizontal-axis wind turbines (HAWTs) for a given rotor radius and free-stream velocity (de Vries, 1979). A second explanation, as argued by de Vries (1979), is that if the sectional lift force of the duct is directed towards the turbine plane, the associated circulation of the duct induces an increased mass flow through the turbine This solution is suited for urban areas where the radius of the rotor is a constraint and the free-stream velocity is low due to the presence of buildings. Tang et al (2018) experimentally investigated the effects of variable duct expansion ratios on the aerodynamic performance of DWTs. As a drawback, for a duct with a large ratio of duct outlet to rotor area, flow separation along the duct inner walls might be present (Aranake et al, 2015; Dighe et al, 2018a).
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