Abstract

Wind tunnel measurements using particle image velocimetry have been performed around two perforated discs, with varying streamwise distance, in order to simulate the wake interaction between wind turbines. The static pressure footprint (p-f) on ground level associated with the wake behind the disc and wake velocity data for both the streamwise and wall-normal velocity components with the corresponding turbulence intensities are reported. The p-f method shows that the size of the wake regions, behind the wind turbine models, initially drop when a second disc is placed just downstream of the first one. From a mutual distance (Δ χ) of about five disc diameters (5D), both wake footprints increase as the mutual distance is increased, and for very large mutual distances, approximately Δ χ/ D > 15, the footprint of the downstream disc has recovered and is about the same as for a single disc. At last we conclude that despite very different inlet conditions to the discs, with about 50% of reduced velocity on the centre line upstream of the second disc and an increase of the maximum streamwise fluctuations by 90%, the mean velocities in the wake are proven to scale with the hub height velocity.

Highlights

  • Inside a wind power farm, the flow field is strongly modified compared to the undisturbed flow

  • In the present paper we present static pressure and velocity data obtained with a pressure plate [17] and particle image velocimetry (PIV), respectively

  • Particle image velocimetry and static pressure measurements of the wake flow behind two perforated discs have been performed in a wind tunnel

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Summary

Introduction

Inside a wind power farm, the flow field is strongly modified compared to the undisturbed flow. Cal et al [8] performed a study with 9 rotating turbine models placed in a boundary layer of a wind tunnel in order to study the mean velocity and turbulence properties, as well as the corresponding impact on the vertical transport of kinetic energy. In the modeled atmospheric boundary layer the two wakes are indistinguishable three rotor diameters downstream of the models This result strongly supports wind turbine interaction studies using porous disc models. A number of numerical and experimental studies have been performed with turbines modelled as porous discs, there is still a need for additional experimental data, both for gaining an increased understanding of wake interaction and for validation of numerical studies. Data of mean velocity in the streamwise and vertical directions are presented, as well as the corresponding turbulence intensities

Wind Tunnel and Measurement Techniques
Flow Configurations
Pressure Measurements
C1: Reference Case with 1 Disc
C2: 2 Discs Positioned 5D Apart in the Streamwise Direction
Varying the Distance to the Second Disc
Findings
Summary and Conclusions

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