CFD and experimental investigations of a novel vertical axis Omni-flow wind turbine shroud system operating at low Reynolds numbers, typical urban flow conditions

Abstract

This study examined the aerodynamic performance and flow characteristics of an innovative shrouded omnidirectional wind turbine system at low Reynold numbers to tackle the SDG 7 of the UN. Four turbulence models, notably the Shear Stress Transport (SST Menter) k − ω, the Reynolds Stress Transport (RST), the Improved Delay Detached Eddies Simulation (IDDES) SST k − ω, and the Large Eddy Simulation (LES WALE), were tested to find the best model(s) for this new omni-flow wind turbine. Compared with experimental results, the LES WALE and the IDDES SST k − ω models best predicted turbulent and uniform flow regions inside and outside the shroud, including CFD parameters, with one being more accurate on specific parameters such as Cd and another on other parameters. The IDDES SST k − ω excelled in predicting velocity ratios, lift coefficient (Cl) and provided the best balance of accuracy and computational efficiency of this innovative omni-direction wind turbine shroud. The novel shroud design, with its unique ability to self-start and harness omnidirectional wind at any free stream velocity for electricity generation, was a key focus of this study. The airflow inside and around the innovative shroud system was meticulously characterised for potential optimisation. Findings demonstrated that the shroud effectively redirected airflow as low as 1.5 m/s into the turbine housing and with 1.5 maximum speed ratio the airflow flew towards the outlet and generated power, leading to superior self-starting capabilities. The power output increased non-linearly with the rotational speed, achieving optimal efficiency beyond 1000 rpm. It is evident that this new system has the potential for enhanced energy capture under varying wind conditions in urban areas.