Performance analysis of small-scale horizontal axis wind turbines with outward leading-edge tubercules

Abstract

This study investigates the effect of outward leading-edge (LE) tubercles on performance of small-scale horizontal axis wind turbines (ss-HAWTs). In the study, the tubercles were placed in a 50 % R (radius) region from the mid to tip of the blade. The tubercle parameters prominent in the literature were applied to the NREL 822 airfoil, and the effectiveness of each tubercle form was evaluated under common operating conditions. The measurements were conducted in the open test section of the blowing type wind tunnel for a 3-blade rotor with a diameter of 0.9 m. The power coefficients were evaluated by keeping the baseline rotor and five different configurations experimentally at different rotational speeds. The initial blade design was simulated with Q-Blade software, and the experimental results were compared with the analytical results in terms of power coefficient (C_P). The present experimental results show that the tubercles perform effectively at high tip speed ratios, regardless of rotational speed. Tubercled blades generally underperform at low tip speed ratios (λ < 4.5) but outperform the baseline at higher λ values. The D3 configuration with the lowest amplitude (A₁ = 0.019) and moderate wavelength (W₁ = 0.176) consistently achieved high C_P values over a wide λ range, particularly at 400 rpm, with up to 37.5 % higher C_P than the baseline at λ ≈ 5.3. In addition, tubercled blades were evaluated to be more adaptable to changes in wind speed ($V$), as the maximum power coefficient was maintained in a wider range in terms of λ. In addition, alternative blade configurations have been observed to offer greater energy production potential at low wind speeds. The surface oil flow visualization (SOFV) technique was employed to analyze the three-dimensional flow field surrounding the turbine blades at a rotational speed of 500 rpm. The findings indicate that the turbine blades with partial distribution of LE tubercle manipulated the flow by disrupting the laminar separation bubble formation observed in the baseline, thereby promoting the flow reattachment and enhancing the turbine performance.