Intracycle angular velocity control of cross-flow turbines

Abstract

Cross-flow turbines, also known as vertical-axis turbines, have numerous features that make them attractive for wind and marine renewable energy. To maximize power output, the turbine blade kinematics may be controlled during the course of the blade revolution, thus optimizing the unsteady fluid dynamic forces. Dynamically pitching the blades, similar to blade control in a helicopter, is an established method. However, this technique adds undesirable mechanical complexity to the turbine, increasing cost and reducing durability. Here we introduce a novel alternative requiring no additional moving parts: we optimize the turbine rotation rate as a function of blade position resulting in motion (including changes in the effective angle of attack) that is precisely timed to exploit unsteady fluid effects. We demonstrate experimentally that this approach results in a 79% increase in power output over industry standard control methods. Analysis of the fluid forcing and blade kinematics show that maximal power is achieved through alignment of fluid force and rotation rate extrema. In addition, the optimized controller excites a well-timed dynamic stall vortex, as is found in many examples of biological propulsion. This control strategy allows a structurally robust turbine operating at relatively low angular velocity to achieve high efficiency and could enable a new generation of environmentally-benign turbines for wind and water current power generation.

Robust flow reconstruction from limited measurements via sparse representation

“…Estimating the structure of a flow field from limited and noisy measurements is an important challenge in many engineering applications. For example, accurate estimation is central to active flow control [1,2,3,4], which has the potential to advance next-generation technology, ranging from fuel-efficient, low-drag automobiles [5] to high-efficiency turbines [6] and internal combustion engines [7]. The ability to reconstruct important flow features from restricted observations is also critical in applications as diverse as cardiac bloodflow modeling [8,9], ship wake identification [10], and climate science [11].…”

Impact of blade mounting structures on cross-flow turbine performance

“…of 18, 23, 27 and 32×10 3 , where ν is the kinematic viscosity. Losses due to drag on the mounting structures were estimated by performing the same tip-speed ratio sweeps with the mounting structures alone, after the method of Bachant et al 16 .…”

“…Despite historical concerns of low performance and structural failure due to fatigue, lift-based cross-flow turbines have experienced a resurgence of research and commercial interest in recent years and hold promise for urban 1 and offshore 2 wind applications. Modern experimental and computational techniques have enabled substantial increases in power performance 3 and suggestions that optimized arrays may be able to extract more power per area than arrays of axial-flow turbines 4 . Drag-based cross-flow turbines are also an area of active research 5 , but are not the focus of this investigation and recent developments (e.g., Plourde et al 6 ) are not discussed here.…”

Performances and Stall Delays of Three Dimensional Wind Turbine Blade Plate-Models with Helicopter-Like Propeller Blade Tips

“…Some researches in stall regulated wind turbines to output power controls have recently been conducted (Bourlis, 2011;Maheswari & Tamilvendhan, 2012;Pereira, Bussel, & Timmer, 2014). Pitch control and fixed pitch mechanisms have also been the subjects of investigations (Boorsma & Schepers, 2016;Farouk & Gawad, 2013;Leroy et al, 2016;Neammanee, Sirisumrannukul, & Chatratana, 2010;Strom, Brunton, & Polagye, 2016;Vijae, 2011). Modified design of wind turbines have also been investigated (Abdulhadi, 2012;Baldacchino et al, 2016;Elfarra, 2011;Lutz & Wagner, 2000;Lynch, 2011;Maniaci et al, 2016;Perfilev, 2013;Rahimi, Hartvelt, Peinke, & Schepers, 2016;Schubel & Crossley, 2012).…”