Computational study of diffuser augmented wind turbine using actuator disc force method

Dighe, Vinit V.; Avallone, Francesco; Bussel, G.J.W. Van

doi:10.2495/cmem-v4-n4-522-531

Cited by 15 publications

(8 citation statements)

References 11 publications

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“…The experimental data is consistent with the simulation results [16]. The small differences between experiment data and numerical calculation may, amongst others, be explained by the small wind tunnel blockage effect.…”

Section: Global Velocity Field In Unloaded Diffuser and Loaded Diffusersupporting

confidence: 80%

Experimental study of flow field of an aerofoil shaped diffuser with a porous screen simulating the rotor

Tang¹,

Avallone²,

Bussel³

2016

Int. J. CMEM

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This study presents an experimental investigation on a diffuser augmented wind turbine (DAWT). A screen mesh is used to simulate the energy extraction mechanisms of a wind turbine in experiment. Different screen porosities corresponding to different turbine loading coefficients are tested. Measurements of the axial force and of the velocity distribution in radial direction are reported. The general purpose is to highlight the dependency between the diffuser and the screen, and to compare the radial velocity distributions in the diffuser between unloaded and loaded conditions. It is shown that the thrust on an unshrouded screen is lower than on a shrouded screen, under the same inflow condition. Moreover, the thrust on the diffuser largely depends on the screen loading. For the present configuration, the thrust on the screen with high loading coefficient contributes for more than 70% of the total thrust on the DAWT. Smoke visualizations and radial velocity profiles reveal that the high loading screen induces flow separation on the outer surface of the diffuser, justifying the results of the thrust measurements. It is also inferred that the flow separation leads to loss of thrust and has a great effect on the total pressure drag. It should be emphasized that the experimental results indicate that the flow field around the diffuser is strongly affected by the choice of screen porosity, that is, turbine loading. And that, the thrust coefficient of the diffuser does not show a linear dependence on the thrust coefficient of the screen. The axial momentum theory, therefore, is not a solid predictor for DAWT performance with high loaded screens.

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Section: Global Velocity Field In Unloaded Diffuser and Loaded Diffusersupporting

confidence: 80%

Experimental study of flow field of an aerofoil shaped diffuser with a porous screen simulating the rotor

Tang¹,

Avallone²,

Bussel³

2016

Int. J. CMEM

Self Cite

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“…When compared with experimental results, for a similar configuration but without forced transition, good agreement is found. As a matter of fact, Dighe et al [14] reported a value of C t equal to 0.81 using the same duct geometry and a porous disc to mimic the isolated rotor.…”

Section: Grid Resolution Studymentioning

confidence: 99%

“…They confirmed that embedding an actuator disk within a duct alters the power coefficient and that the interaction affects the actuator loading at which the optimal power coefficient is reached. As a consequence, the coupling of a rotor with optimal thrust coefficient with a duct might result in a non-optimal ducted wind turbine [14,15]. The discussed analytical models are based on the assumption of an uniformly loaded actuator disk, which is not representative of realistic rotors.…”

Section: Introductionmentioning

confidence: 99%

“…For this reason, the DonQi ® wind turbine has been selected because of the availability of reference data and of the geometry. As a matter of fact, Tang et al [15] performed experimental measurements embedding a uniformly loaded perforated disk into the duct and Dighe et al [14] carried out two-dimensional RANS simulation of the same configuration. The outcome of this research represents the first available dataset on a realistic wind turbine that can be used by other researchers to validate analytical and semi-analytical models.…”

Section: Introductionmentioning

confidence: 99%

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On the Effect of the Tip Clearance on the Aerodynamic and Aeroacoustics of a Diffuser-Augmented Wind Turbine

Avallone

Casalino

Ragni

2019

AIAA Scitech 2019 Forum

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A computational study of two Diffuser-Augmented Wind Turbines (DAWTs) is carried out to investigate both the hydrodynamic flow field and the far-field noise. The two configurations differ for the tip-clearance ratio, defined as the ratio between the tip clearance and the rotor radius. The DonQi ® wind turbine, a three blades ducted rotor, is adopted as baseline configuration because of the availability of reference data. It has a tip-clearance ratio of 2.5%. The second configuration is obtained from the first one by elongating the rotor radius such to force the interaction between the turbulent boundary layer, developing over the suction side of the diffuser, and the tip of the blades, thus resulting in a tip-clearance ratio of 0.7%. The rotor with the longer blades shows a reduction of the thrust coefficient because of the lower lift generated by the diffuser that results in a lower axial velocity at the rotor plane. It is shown that this is caused by the smaller tip gap that forces the break down of the rotor tip vortex in smaller turbulent structures immediately after the rotor plane and that induces earlier flow separation along the suction side of the diffuser. The tip-clearance ratio has also a strong effect on the far-field noise. For angles between 60 • and 120 • , where 0 • corresponds to the axial upstream direction, the blade tonal noise, at frequency equal to the blade passing frequency and higher harmonics, is the dominant source. For other angular directions, noise increase is found for the smaller tip-clearance ratio case associated to an additional noise source, that becomes dominant, linked to an increase of the energy content of velocity fluctuations in the gap region. This noise source, that can be modeled as a monopole source located in the gap, causes an increase of broadband noise at frequencies higher than the third blade passing frequency and a tonal peak at a frequency equal to 4.5 times the blade passing frequency and higher harmonics.

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“…There are several approaches to solve the flow equations around an AD. One of these approaches is based on the use of classical Computational Fluid Dynamics (CFD) techniques [1][2][3][4] and for this reason it will be named CFD-AD [5][6][7][8][9][10][11]. In this method, the Euler (or Navier-Stokes) equations are solved by finite volume or difference schemes, while the presence of the turbine is modelled by activating the momentum source terms in a disk-shaped region.…”

Section: Introductionmentioning

confidence: 99%

Effects of the Approximations Embodied in the Momentum Theory as Applied to the NREL PHASE VI Wind Turbine

Bontempo

Manna

2017

IJTPP

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This paper investigates the impact of the standard approximations embodied in the well-known Momentum Theory on its performance prediction capabilities. To this aim, the results of the momentum theory, which is still widely used in all Blade Element/Momentum codes for the analysis and/or design of wind turbines, are compared with those obtained with an actuator disk model based on Computational Fluid Dynamics techniques. In this method, the axisymmetric and steady Euler equations are solved with a classical finite volume approach, while the turbine effects are modelled through a set of axial and tangential body forces distributed over a disk shaped region representing the rotor swept surface. Since this method does not rely on the momentum theory simplifying assumptions, it can be suitably employed to verify the momentum theory validity. The analysis is carried out using the well documented experimental data of the National Renewable Energy Laboratory Phase VI wind turbine.

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Computational study of diffuser augmented wind turbine using actuator disc force method

Cited by 15 publications

References 11 publications

Experimental study of flow field of an aerofoil shaped diffuser with a porous screen simulating the rotor

Experimental study of flow field of an aerofoil shaped diffuser with a porous screen simulating the rotor

On the Effect of the Tip Clearance on the Aerodynamic and Aeroacoustics of a Diffuser-Augmented Wind Turbine

Effects of the Approximations Embodied in the Momentum Theory as Applied to the NREL PHASE VI Wind Turbine

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