COMPUTATIONAL AND EXPERIMENTAL ANALYSIS OF A DIFFUSER THAT CONSTITUTES A CONCEPTUAL AND UNPRECEDENTED DAWT FOR URBAN APPLICATIONS

Abstract

This article presents numerical analyses of diffusers formed by different curved aerodynamic profiles and high lift-to-drag ratio airfoils, with and without the use of a ring flap (flanged diffuser) applied externally at the diffuser exit. The objective is to identify the optimal geometry for the fabrication of a full-scale prototype of a DAWT (Diffuser-Augmented Wind Turbine), which is a conceptual and innovative design developed for urban and rural use. The diffuser aims to increase the mass flow rate through the turbine, allowing for greater power extraction at low wind speeds caused by surrounding buildings. The mass flow increment factor is used as a performance parameter for the diffuser and it is found to have an approximately linear growth with the sum of radial forces, which is related to the lift coefficient of the employed aerodynamic profile. Both the application of the ring flap and the axial length of the diffuser generate higher radial forces and increase the mass flow rate through the diffuser. The diffuser with the NACA 2421 airfoil profile demonstrated a mass flow increment of 1.42 in a configuration with a flap and a configuration without a flap but with a longer axial length. The flap causes higher drag force and higher standard deviation. Therefore, for the fabrication of the turbine prototype, a flanged diffuser with the NACA2421 airfoil profile is chosen. By comparing the numerical and experimental results of diffusers with the NACA2421 airfoil profile, it is concluded that the experimentally obtained velocity increment is 7% lower than the increment indicated by numerical simulations.