Wind Tunnel Probe Into an Array of Small-Scale Horizontal-Axis Wind Turbines Operating at Low Tip Speed Ratio Conditions

Abstract

In recent times, the small wind farms consisting of small-scale horizontal-axis wind turbines (SHAWTs) have emerged as a suitable candidate for electric power generating system. In view of this, an experimental study on the arrays of two SHAWTs has been performed in a wind tunnel to find the individual/combined performance(s) along with the downstream wake assessment. The rotor blades composed of Eppler E216 airfoil and of radius (=120 mm) are designed using the blade element momentum theory. The operational limit of tip speed ratio (λ) is kept between 0.5 and 6. The upstream turbine (UsT) is capable to produce a maximum power coefficient (Cpmax) of 0.30 at a wind speed U=8 m/s, whereas at the same wind speed, the downstream turbine (DsT) produces Cpmax values of 0.12, 0.13, and 0.15 when installed at a distance of 6R, 8R and 10R from the UsT, respectively. Another notable feature is the change in operational limit of λ for DsT due to the wake of UsT. The streamwise velocity measurement at the different downstream locations of UsT shows the formation of W-shape velocity deficit within the near wake regime that loses its shape as the distance downstream goes beyond 12R due to ~60-70% flow recovery.

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