Hybrid CFD-source Terms Modelling of a Diffuser-augmented Vertical Axis Wind Turbine

Letizia, Stefano; Zanforlin, Stefania

doi:10.1016/j.egypro.2016.11.144

Cited by 11 publications

(14 citation statements)

References 23 publications

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“…Nowadays, especially in wind turbine applications, these models are coupled with simple body representations (also known as actuator models) to be used in numerical simulations to reduce their computational costs (see, eg, previous works).…”

Section: Introductionmentioning

confidence: 99%

A simple model for deep dynamic stall conditions

et al. 2020

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The present study is focused on modeling of dynamic stall behavior of a pitching airfoil. The deep stall regime is in particular considered. A model is proposed, which has a low implementation and computational complexity but yet is able to deal with different types of dynamic stall conditions, including those characterized by multiple vortex shedding at the airfoil leading edge. The proposed model is appraised against an extensive data set of experimental (α,CL) curves for NACA0012. The results of an existing widely used model, having comparable complexity, are also shown for comparison. The proposed model is able to well reproduce not only the classic curves of deep dynamic stall but also the curves characterized by lift oscillations at high angles of attack due to the shedding of multiple vortices. Furthermore, the model appears to be robust to variations of its parameters from the optimal values and of the airfoil geometry. Finally, the model is successfully implemented in a commercial CFD software and applied to the simulation of a vertical axis wind turbine within the actuator cylinder approach. The accuracy of the prediction of the turbine power coefficient in the whole rotation cycle is very good for the optimal working condition of the turbine, for which the model parameters were calibrated. Fairly good accuracy is also obtained in significantly different working conditions without any further calibration.

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Section: Introductionmentioning

confidence: 99%

A simple model for deep dynamic stall conditions

et al. 2020

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“…A difficulty encountered by the designers of high performance diffusers is that the behaviour of an empty diffuser is completely different from that of a diffuser with a rotor working inside. Thus, numerical tools adopted to predict a new diffuser performance (CFD, or low order methods [29,30]) should also consider the turbine presence. Preliminary simulations of our diffusers (without turbines) predicted a slight flow separation in the final part of the inner walls for the hydrofoil shaped diffuser, and a massive separation for the symmetrical one leading to a 24% lower flow rate.…”

Section: P Of the Turbine Pairsmentioning

confidence: 99%

“…Malipeddi et al [27] carried out a CFD optimization of the diffuser shape, calculating a power increment of 60% and a considerable reduction of the torque ripple. The aerodynamics of CFTs inserted in air/hydro-foil shaped diffusers has been analysed in [28][29][30]. Geurts et al [28], by means of a potential flow solver, predicted a maximum power increment of 80%.…”

Section: Introductionmentioning

confidence: 99%

“…Geurts et al [28], by means of a potential flow solver, predicted a maximum power increment of 80%. Letizia and Zanforlin [29] by means of 2D CFD, reported a remarkable power increase due to the interaction of diffuser and turbine, whose presence allow to prevent the stall onset in the diffuser's throat. Instead of a single turbine, the HARVEST system [30,31] is equipped with a pair of contra-rotating H-Darrieus turbines that are mounted in a hydrofoil shaped diffuser.…”

Section: Introductionmentioning

confidence: 99%

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Performance Analysis of Hydrofoil Shaped and Bi-Directional Diffusers for Cross Flow Tidal Turbines in Single and Double-Rotor Configurations

2019

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With the aim of finding efficient solutions for cross flow turbine (CFT) bi-directional diffusers able to harvest non perfectly rectilinear tidal currents, a 2D CFD analysis of ducted CFTs was carried out with focus on the effects of diffuser shape and yaw angle. The HARVEST hydrofoil shaped diffuser, equipped with a pair of counter-rotating turbines, and a bi-directional symmetrical diffuser were compared in terms of coefficient of power (CP), torque ripple, overall thrust on diffuser and wake characteristics. Slightly better CP were predicted for the symmetrical diffuser, due to the convergent walls that address the flow towards the blade with a greater attack angle during early and late upwind and to the viscous interactions between the turbine wakes and strong vortices shed by the diffuser. A CP’s extraordinary improving resulted when yaw increased up to 22.5° for the hydrofoil shaped and up to 30° for the symmetrical diffuser. Similar behaviour in yawed flows also occurred in case of a ducted single rotor, demonstrating that it is a characteristic of CFTs. The insertion of a straight throat in the diffuser design proved to be an effective way to mitigate torque ripple, but a CP loss is expected.

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“…The novelty respect to the current approaches is that the turbine geometrical parameters and the rotation speed are included, since they determine the loading (lift and drag) on the blade. It must be noted that hybrid BEM-CFD models for CFTs are increasingly used by engineers to predict the turbine performance in applications of practical interest [33][34][35][36][37][38]. However, despite the computational costs being significantly less than in the case of high-fidelity fully CFD simulations, the complexity of the models and the refinement of grids limit their use to the simulation of a single turbine.…”

Section: Introductionmentioning

confidence: 99%

Embedding of a Blade-Element Analytical Model into the SHYFEM Marine Circulation Code to Predict the Performance of Cross-Flow Turbines

Pucci

Bellafiore

Zanforlin

et al. 2020

JMSE

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Our aim was to embed a 2D analytical model of a cross-flow tidal turbine inside the open-source SHYFEM marine circulation code. Other studies on the environmental impact of Tidal Energy Converters use marine circulation codes with simplified approaches: performance coefficients are fixed a priori regardless of the operating conditions and turbine geometrical parameters, and usually, the computational grid is so coarse that the device occupies one or few cells. In this work, a hybrid analytical computational fluid dynamic model based on Blade Element Momentum theory is implemented: since the turbine blades are not present in the grid, the flow is slowed down by means of bottom frictions applied to the seabed corresponding to forces equal and opposite to those that the blades would experience during their rotation. This simplified approach allowed reproducing the turbine behavior for both mechanical power generation and the turbine effect on the surrounding flow field. Moreover, the model was able to predict the interaction between the turbines belonging to a small cluster with hugely shorter calculation time compared to pure Computational Fluid Dynamics.

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Hybrid CFD-source Terms Modelling of a Diffuser-augmented Vertical Axis Wind Turbine

Cited by 11 publications

References 23 publications

A simple model for deep dynamic stall conditions

A simple model for deep dynamic stall conditions

Performance Analysis of Hydrofoil Shaped and Bi-Directional Diffusers for Cross Flow Tidal Turbines in Single and Double-Rotor Configurations

Embedding of a Blade-Element Analytical Model into the SHYFEM Marine Circulation Code to Predict the Performance of Cross-Flow Turbines

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