Coriolis Effect on Dynamic Stall in a Vertical Axis Wind Turbine

Tsai, Hsieh-Chen; Colonius, Tim

doi:10.2514/1.j054199

Cited by 45 publications

(14 citation statements)

References 28 publications

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“…12 As presented in Dunne et al, 13 the computational results have a good agreement with experiments performed by Dunne and McKeon. 14 Current study aims at numerically investigating the self-starting capability of a VAWT using the immersed boundary projection method.…”

Section: Introductionsupporting

confidence: 81%

Numerical Investigation of Self-Starting Capability of Vertical-Axis Wind Turbines at Low Reynolds Numbers

Tsai

Colonius

2016

34th AIAA Applied Aerodynamics Conference

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The self-starting capability of a NACA 0018 multi-bladed vertical-axis wind turbine is numerically investigated. The immersed boundary method is used to simulate the flow around a two-dimensional cross section of the wind turbine and the predictor-corrector method is used to couple the equation of motion of the turbine. A simple load model, which is linearly proportional to turbine angular velocity, is used for the load of the turbine. The angular velocity is characterized as a function of Reynolds number, density ratio, and viscous coefficient of the proposed load model. The power outputs and moment coefficients of motor-driven and flow-driven vertical-axis wind turbine are compared. For a particular Reynolds number, as the load on the flow-driven turbine is increased, the tip speed is reduced until the turbine fails to coherently rotate. The flow-driven and motordriven moment coefficients in the computation have good agreement between each other and are qualitatively similar to the torque measured in experiments. 1 These computations suggest that the load of a flow-driven turbine can be well-represented by the proposed load model and a motor-driven turbine can reproduce the physics of a flow-driven turbine within the range of tip-speed ratio examined. A simple model is proposed in order to analyze the starting torque. By assuming that the inertia of the blade is much larger than the fluid, the turbine can be considered stationary in the flow. The starting torque distribution of a multi-bladed turbine indicates the important orientations corresponding to maximum torque generation, at which a self-starting turbine always starts, and a stable equilibrium, where a non-self-starting turbine oscillates. These features agree with observations from the full simulations of the starting process. We further model the starting torque distribution by considering a single blade at different orientations, and construct starting torque distributions for multi-bladed turbines by linearly combining the torques at the respective positions of the blades. We show that this approximation is valid for a sufficiently low turbine solidity of about 0.5. Using this model, we find optimal starting configuration for a multi-bladed low-solidity vertical-axis wind turbine. Nomenclaturec airfoil chord length C M moment coefficient C P power coefficient F friction coefficient of the load I O moment of inertia of the blade about the rotation center of the VAWT N b number of blades O turbine rotation center R radius of the turbine Re Reynolds Number t * convective time units U ∞ freestream velocity

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Section: Introductionsupporting

confidence: 81%

Numerical Investigation of Self-Starting Capability of Vertical-Axis Wind Turbines at Low Reynolds Numbers

Tsai

Colonius

2016

34th AIAA Applied Aerodynamics Conference

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“…The empirically determined functional dependencies were used for the Reynolds number term and for the dynamic effects, where is given by (3.4) and can be found using the functional relationship given by (3.3) and shown in Figure 7. Variations in and drove unsteady effects such as dynamic stall, Coriolis and centrifugal forces as well as wake–blade interactions (see for example Rezaeiha, Montazeri, & Blocken, 2018; Tsai & Colonius, 2016). Given this, a variation in the Reynolds number appeared to only affect the quasisteady physics of the VAWT, such as airfoil boundary layer development, while leaving the dynamic phenomena unaltered.…”

Section: Resultsmentioning

confidence: 99%

Solidity effects on the performance of vertical-axis wind turbines

Miller

Subrahmanyam

Hultmark

2021

Flow

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The variety of configurations for vertical-axis wind turbines (VAWTs) make the development of universal scaling relationships for even basic performance parameters difficult. Rotor geometry changes can be characterized using the concept of solidity, defined as the ratio of solid rotor area to the swept area. However, few studies have explored the effect of this parameter at full-scale conditions due to the challenge of matching both the non-dimensional rotational rate (or tip speed ratio) and scale (or Reynolds number) in conventional wind tunnels. In this study, experiments were conducted on a VAWT model using a specialized compressed-air wind tunnel where the density can be increased to over 200 times atmospheric air. The number of blades on the model was altered to explore how solidity affects performance while keeping other geometric parameters, such as the ratio of blade chord to rotor radius, the same. These data were collected at conditions relevant to the field-scale VAWT but in the controlled environment of the lab. For the three highest solidity rotors (using the most blades), performance was found to depend similarly on the Reynolds number, despite changes in rotational effects. This result has direct implications for the modelling and design of high-solidity field-scale VAWTs.

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“…The breadth of this parameter space suggests optimization by reduced-order models, but this is complicated by the unsteady nature of cross-flow turbine fluid dynamics. The blade's angle of attack varies throughout the turbine's rotation, potentially inducing dynamic stall 16,17 , and the blades pass disturbed flow during their downstream sweep, potentially interacting with coherent structures. Such dynamics are difficult to generalize to the full range of rotor geometries.…”

Section: Introductionmentioning

confidence: 99%

“…Unlike blade element momentum (BEM) models for axial-flow turbines 18 , analytical models [19][20][21] are often only valid for a specific configuration. Similarly, the challenges of simulating unsteady boundary layer dynamics 16,17 , combined with a lack of exploitable circumferential symmetry and a necessity for high spatial and temporal resolution 22 , make accurate two-dimensional simulations computationally expensive. Threedimensional simulations, which are even more expensive, are required to fully incorporate the effects of span-wise flow, mixing, and parasitic torque from blade supports [23][24][25] .…”

Section: Introductionmentioning

confidence: 99%

Effect of aspect ratio on cross-flow turbine performance

Hunt

Stringer

Polagye

2020

Journal of Renewable and Sustainable Energy

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Cross-flow turbines convert kinetic power in wind or water currents to mechanical power. Unlike axial-flow turbines, the influence of geometric parameters on turbine performance is not well-understood, in part because there are neither generalized analytical formulations nor inexpensive, accurate numerical models that describe their fluid dynamics. Here, we experimentally investigate the effect of aspect ratiothe ratio of the blade span to rotor diameter -on the performance of a straight-bladed cross-flow turbine in a water channel. To isolate the effect of aspect ratio, all other non-dimensional parameters are held constant, including the relative confinement, Froude number, and Reynolds number. The coefficient of performance is found to be invariant for the range of aspect ratios tested (0.95 -1.63), which we ascribe to minimal blade-support interactions for this turbine design. Finally, a subset of experiments is repeated without controlling for the Froude number and the coefficient of performance is found to increase, a consequence of Froude number variation that could mistakenly be ascribed to aspect ratio. This highlights the importance of rigorous experimental design when exploring the effect of geometric parameters on cross-flow turbine performance.

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Coriolis Effect on Dynamic Stall in a Vertical Axis Wind Turbine

Cited by 45 publications

References 28 publications

Numerical Investigation of Self-Starting Capability of Vertical-Axis Wind Turbines at Low Reynolds Numbers

Numerical Investigation of Self-Starting Capability of Vertical-Axis Wind Turbines at Low Reynolds Numbers

Solidity effects on the performance of vertical-axis wind turbines

Effect of aspect ratio on cross-flow turbine performance

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