Experimental and Numerical Quantification of Radial Flow in the Root Region of a HAWT Blade

Akay, B.; Ferreira, Carlos; Bussel, G.J.W. Van; Herráez, Iván

doi:10.2514/6.2012-896

Cited by 3 publications

(1 citation statement)

References 10 publications

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“…A stereoscopic PIV set-up has been installed on a traversing system able to scan the flow field in the wake of the horizontal-axis wind-turbine wake, as shown in figure 3. This measurement set-up has already proved suitable to obtain both the load distribution on the blade (Ragni, Oudheusden & Scarano 2011) and the evolution of vorticity in the wake of a wind turbine (Akay et al 2012). The required illumination is provided by a Quantel Evergreen Nd:YAG laser system with an average output of 200 mJ pulse −1 .…”

Section: Stereoscopic Particle Image Velocimetrymentioning

confidence: 99%

Tip-vortex instability and turbulent mixing in wind-turbine wakes

et al. 2015

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Kinetic-energy transport and turbulence production within the shear layer of a horizontal-axis wind-turbine wake are investigated with respect to their influence on the tip-vortex pairwise instability, the so-called leapfrogging instability. The study quantifies the effect of near-wake instability and tip-vortex breakdown on the process of mean-flow kinetic-energy transport within the far wake of the wind turbine, in turn affecting the wake re-energising process. Experiments are conducted in an open-jet wind tunnel with a wind-turbine model of 60 cm diameter at a diameter-based Reynolds number range Re D = 150 000-230 000. The velocity fields in meridian planes encompassing a large portion of the wake past the rotor are measured both in the unconditioned and the phase-locked mode by means of stereoscopic particle image velocimetry. The detailed topology and development of the tip-vortex interactions are discussed prior to a statistical analysis based on the triple decomposition of the turbulent flow fields. The study emphasises the role of the pairing instability as a precursor to the onset of three-dimensional vortex distortion and breakdown, leading to increased turbulent mixing and kinetic-energy transport across the shear layer. Quadrant analysis further elucidates the role of sweep and ejection events within the two identified mixing regimes. Prior to the onset of the instability, vortices shed from the blade appear to inhibit turbulent mixing of the expanding wake. The second region is dominated by the leapfrogging instability, with a sudden increase of the net entrainment of kinetic energy. Downstream of the latter, random turbulent motion characterises the flow, with a significant increase of turbulent kinetic-energy production. In this scenario, the leapfrogging mechanism is recognised as the triggering event that accelerates the onset of efficient turbulent mixing followed by the beginning of the wake re-energising process.

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Section: Stereoscopic Particle Image Velocimetrymentioning

confidence: 99%

Tip-vortex instability and turbulent mixing in wind-turbine wakes

et al. 2015

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The role of conservative forces in rotor aerodynamics

et al. 2014

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The theory to predict the performance and loads on rotors (propellers, screws,\ud windmills) has a history of more than a century. Apart from modern computational\ud fluid dynamics and vortex panel models taking the true blade geometry into account,\ud most other models proceed from an infinitely thin actuator disc or line. These models\ud assume an externally defined force field distributed at the disc or line, representing\ud the loads on the real rotor. Given this force field, the flow is solved by momentum\ud balances or by the equations of motion. The use of external force fields was discussed\ud in textbooks of the first decades of the 20th century, but has received little attention\ud since then. This paper investigates the higher-order effect of adding thickness to the\ud actuator disc or changing the actuator line to a blade with cross-sectional dimensions.\ud For the generation of a Rankine vortex by a force field acting on an actuator disc with\ud thickness, an exact solution has been found in which not only the thrust and torque\ud determine the flow, but also a radial force. This force is conservative, in contrast to\ud the other force components. For rotor blades, a conservative normal and radial force\ud acting on the chordwise bound vorticity is present. This explains the experimentally\ud observed inboard motion of the tip vortex of model wind turbine rotors before the\ud wake induction field drives it outboard. Simulations by computational fluid mechanics\ud and a vortex panel code reproduce the inboard motion, but an actuator line analysis,\ud in which the chordwise vorticity is absent, does not. The conservative load is only\ud 1–2% of the thrust on the entire blade but =10% of the thrust at the tip (r/R>0.9).\ud Conservative forces at the disc and rotor blade vanish for vanishing disc thickness or\ud blade cross-section, so play no role in any of the infinitely thin actuator disc or line\ud methods. However, if higher-order effects of non-zero dimensions are to be modelled,\ud the conservative force field has to be included.peer-reviewe

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On the Turbulent Mixing in Horizontal Axis Wind Turbine Wakes

Lignarolo

2016

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Experimental and Numerical Quantification of Radial Flow in the Root Region of a HAWT Blade

Cited by 3 publications

References 10 publications

Tip-vortex instability and turbulent mixing in wind-turbine wakes

Tip-vortex instability and turbulent mixing in wind-turbine wakes

The role of conservative forces in rotor aerodynamics

On the Turbulent Mixing in Horizontal Axis Wind Turbine Wakes

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