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

Abstract

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 $Re_D = 6.3\times 10^5$ and surge-velocity amplitudes up to 24 % of the wind speed. The combined modelling 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 modelling 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.

Resolvent-based motion-to-wake modelling of wind turbine wakes under dynamic rotor motion

“…As seen, FT (r) and CT (r) are almost unaffected by the rotor motion, because the oscillatory motion is relatively small, which is consistent with the experiments with model wind turbine rotors (Fontanella et al 2022;Meng et al 2022a). From the theoretical aspect, recent studies of Wei & Dabiri (2023) and Heck, Johlas & Howland (2023) have established relations between the thrust force for wind turbines with surge motion velocity amplitudes and yaw angles. For example, Wei & Dabiri (2023) has shown that the time-averaged rotor thrust of a periodically surging wind turbine ( FT ) is related to that of a stationary wind turbine FT,0 as follows:…”

“…Nonlinear effects are not considered by the present model, but it is of interest to take them into account in future. In this regard, the M2F model should be modified to include the nonlinear rotor forcing due to large rotor motion, as shown recently by Heck et al (2023) and Wei & Dabiri (2023); the F2W model should also take into account the interaction between modes and the wake-response-induced modifications of the time-averaged wake and the eddy viscosity. This can be achieved via an iterative approach as demonstrated by Rosenberg & McKeon (2019) in turbulent channel flows.…”

“…From the theoretical aspect, recent studies of Wei & Dabiri (2023) and Heck, Johlas & Howland (2023) have established relations between the thrust force for wind turbines with surge motion velocity amplitudes and yaw angles. For example, Wei & Dabiri (2023) has shown that the time-averaged rotor thrust of a periodically surging wind turbine ( FT ) is related to that of a stationary wind turbine FT,0 as follows:…”

Modeling unsteady loads on wind-turbine blade sections from periodic structural oscillations and impinging gusts

“…While analytical models for the time response of the full turbine rotor have recently been derived and experimentally validated (e.g. Mancini et al, 2020;Wei and Dabiri, 2023), these have not yet been connected to unsteady aerodynamics at the blade-section level. In the case of blade sections undergoing dynamic stall in large-amplitude disturbances, the semi-empirical model of Leishman and Beddoes (1989) may be employed at a blade-section level.…”