Performance enhancement of Ducted Wind Turbines under yawed flow using optimized tubercled ducts: An investigative study

Yawed inflow conditions in urban areas and their impact on Ducted Wind Turbine (DWT) performance has been given very little attention. The current study introduces a novel airfoil-based duct design featuring leading-edge tubercles. Five design factors were selected for optimization: duct stagger angle, tubercle amplitude, tubercle wavenumber, rotor–duct tip gap, and duct fineness ratio. A Taguchi-CFD-Regression model was employed, assessing experiments from an L25 orthogonal array using hybrid RANS-LES models to determine optimal designs and derive empirical relations. Comparative analysis of bare turbines and tubercled DWTs revealed rotor thrust and power augmentation factors of 1.47 and 2.15 under nominal flow conditions. As the inflow yaw angle increased, the tubercled DWTs displayed significant improvements, with a maximum power augmentation factor of 3.28 at a yaw angle of 25°. Tubercles effectively redirected airflow, reducing flow separation and asymmetric loading on the rotor and duct. With effective flow redirection towards the rotor plane and suppression of flow separation within the duct walls, only a negligible 3.2% variation in the blade loading 2.9% in the duct surface pressure was observed between the leeward and windward sides. Flow analysis also demonstrated enhanced rotor–duct tip vortex dissipation and diminished vortex shedding coherency, a prime indicator for tonal noise reduction. Thus, DWTs with tubercles can outperform standard DWTs and bare turbines under yawed flows.