Power-generation enhancements and upstream flow properties of turbines in unsteady inflow conditions

• Published in: arXiv.org 2023-05
• Main Authors: Wei, Nathaniel J, Dabiri, John O
• Format: Article
• Language: English
• Subjects: Amplitudes; Circuits; Deceleration; Diameters; Energy harvesting; Flow velocity; Fluid flow; Inflow; Modelling; Momentum theory; Offshore energy sources; Potential flow; Reynolds number; Tidal power generation; Turbines; Unsteady flow; Upstream; Wind speed; Wind tunnels; Wind turbines
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2210.14466

Energy-harvesting systems in complex flow environments, such as floating offshore wind turbines, tidal turbines, and ground-fixed turbines in axial gusts, encounter unsteady streamwise flow conditions that affect their power generation and structural loads. In some cases, enhancements in time-averaged power generation above the steady-flow operating point are observed. To characterize these dynamics, a nonlinear dynamical model for the rotation rate and power extraction of a periodically surging turbine is derived and connected to two potential-flow representations of the induction zone upstream of the turbine. The model predictions for the time-averaged power extraction of the turbine and the upstream flow velocity and pressure are compared against data from experiments conducted with a surging-turbine apparatus in an open-circuit wind tunnel at a diameter-based Reynolds number of \(Re_D = 6.3\times10^5\) and surge-velocity amplitudes of up to 24% of the wind speed. The combined modeling approach captures trends in both the time-averaged power extraction and the fluctuations in upstream flow quantities, while relying only on data from steady-flow measurements. The sensitivity of the observed increases in time-averaged power to steady-flow turbine characteristics is established, thus clarifying the conditions under which these enhancements are possible. Finally, the influence of unsteady fluid mechanics on time-averaged power extraction is explored analytically. The theoretical framework and experimental validation provide a cohesive modeling approach that can drive the design, control, and optimization of turbines in unsteady flow conditions, as well as inform the development of novel energy-harvesting systems that can leverage unsteady flows for large increases in power-generation capacities.