Conceptual design of airborne contra rotating VAWTs for rooftop wind energy

Co-rotating, counter, and contra-rotating Vertical Axis Wind Turbines (VAWTs) offer higher power yields than singular turbines due to synergetic interactions, making them ideal for rooftop applications. This study focuses on enhancing the efficiency of a Contra-Rotating VAWT (CR-VAWT) using a ducted airborne configuration. A wind gathering device (WGD), optimized via the Taguchi method, is integrated around the CR-VAWT, which is elevated using an oblate spheroid aerostat designed through a force-weight approach. CFD analyses reveal that incorporating the WGD boosts power output by 32% and increases instantaneous torque by 40% during dynamic stall. The WGD enhances flow redirection towards the rotor plane, achieving a 58% power gain at a 10°skew angle. By suppressing blade-tip vortex shedding, the WGD not only improves efficiency but may also reduce noise. This portable system is suitable for rooftops with limited space, requiring fewer turbines to meet energy demands while reducing noise and improving aesthetics. It also allows for integration with other renewable technologies like photovoltaics, promoting sustainability and lowering carbon footprints. A comprehensive implementation framework is presented to support future research on airborne VAWTs.