Aerodynamic Enhancement and Reduced Order Modeling of Vertical Axis Wind Turbines

Abstract

Vertical-axis wind turbines (VAWTs) are recognized as a viable solution for wind energy harvesting. This study discusses VAWT performance in different aspects. First, using computational fluid dynamics (CFD) simulations, the impact of various deflector angles as an auxiliary augmentation on turbine efficiency is examined. Specifically, the deflector orientation angle effect on the dual-rotor straight blade vertical-axis wind turbine (DR-SBVAWT) performance is conducted. Two-dimensional transient simulations were performed for this parametric study. The results demonstrate that deflector implementation boosts the DRSBVAWT self starting capabilities and enhances overall performance. With a vertical deflector (β = 0◦from the y-axis) yields the best performance, providing the highest efficiency and power output. In contrast, a horizontal deflector (angle of β = 90◦ counterclockwise from the y-axis) shows minimal impact on the turbine's performance, suggesting that further angle variations do not significantly enhance the system. Moreover, sensitivity analysis was performed to evaluate the impact of small changes in the deflector orientation that shows β = 0◦ holds the best orientation and small angle variations in deflector orientation show minimal impact on the overall performance of the turbine. In steady-state conditions, the vertical deflector angle increases the tip speed ratio (TSR) of the DR-SBVAWT performance by 11.5% compared to a conventional DR-SBVAWT without the deflector. Additionally, this vertical configuration achieved a 30.15% increase in efficiency at TSR = 2.5, showing its effectiveness in improving overall aerodynamic performance. This parametric study overall provides valuable insights into the optimal deflector angle configuration as an auxiliary augmentation system for dual-rotor vertical axis wind turbines, contributing to the design optimization and improved performance of wind energy systems. Secondly, utilizing the same method of a 2D transient unsteady Reynolds-averaged Navier– Stokes (URANS) numerical simulations, different clustering scenarios of DR-SBVAWT for farm design are studied. Twelve clustering configurations include vertically aligned pairs and staggered clusters of three turbines at different inter-turbine distances, to evaluate their impact on power capture and land usage for the DR-SBVAWT, are investigated. Performance indices, namely, total power coefficient and improvement relative to standalone turbines, are analyzed. Wake effects are qualitatively discussed through detailed velocity contour plots of the wind field. Results show that a DR-SBVAWT turbine arrangement can enhance wind farm performance by approximately 25% for two turbines and about 20% for three staggered turbines, with required spacing of 1.5D and 2.5-3D, respectively. The study overall provides critical insights into the optimal placement and configuration of DR-SBVAWTs for maximizing energy output while minimizing land usage, offering guidance for the design of more efficient VAWT farms. Furthermore, it offers guidance on mitigating destructive interference from upstream turbines, enabling the optimization of multi-turbine layouts so that each unit operates under stable flow conditions. Finally, a reduced order model (ROM) is investigated for VAWT. A novel and robust CFDROM framework is built to evaluate the complex flow field behaviour of a single rotor 3-blade VAWT. A data-driven framework was developed following high-fidelity transient simulations conducted using the URANS simulations within a finite volume method (FVM) framework in ANSYS Fluent. A snapshot-based proper orthogonal decomposition (POD) reduced-order model was developed. Additionally, a domain decomposition strategy was implemented to analyze the flow behavior across the interface between subdomains (the rotor domain and its surrounding domain) of VAWT. To ensure accurate enforcement of interface continuity conditions, the coupling between the inner and outer domains was achieved through a tunable proportional controller (computational gain). Results reveal that domain decomposition approach coupled with ROMs enhances the robustness of the computational cost while maintaining acceptable accuracy. By adding the computational controller, it helps to improve the coupling of the two ROMs, ensuring more efficient integration with fewer mismatches at the interface between the decomposed domains. The data-driven novel framework provides a critical stepping point to extending research to include more complexity of flow dynamics of VAWTs. This proposed framework proves a speedup on the order of one for 300 snapshots, or on about order of four for complete transient simulations (20 seconds) of fixed VAWT. Overall, given the greater viability and applicability of VAWTs in different setups compared to other turbine types, these three detailed studies of dual-rotor design, farm design, and ROM for VAWT, offer a comprehensive framework for understanding VAWT aerodynamics and provide more efficient, high-fidelity design and analysis that benefits in varied wind environments.