425 SARAVANAN et al: PRESSURE DISTRIBUTION OF SMALL WIND TURBINE BLADES WITH WINGLET Journal of Scientific & Industrial Research Vol. 71, June 2012, pp. 425-429 *Author for correspondence E-mail: saro.aero@gmail.com Pressure distribution of rotating small wind turbine blades with winglet using wind tunnel P Saravanan 1 * K M Parammasivam 2 and Selvi Rajan 3 1 Department of Aeronautical Engineering, Tagore Engineering College, Chennai 600 048, India 2 Department of Aerospace Engineering, MIT Campus, Anna University, Chennai 600 044, India 3 Wind Engineering Laboratory, CSIR-Structural Engineering Research Centre (SERC), Chennai 600 113, India Received 18 January 2012; revised 16 April 2012; accepted 17 April 2012 This study presents pressure distribution over an envelope of blade with and without winglets for a small wind turbine in boundary layer wind tunnel. Different winglet configurations were tried based on winglet height and curvature radius. Pressure measurements were made with different chordwise and spanwise locations on the blade with and without winglets nearby tip region. Winglet improves overall pressure difference between pressure surface and suction surface. Presence of winglet seemed to have the pressure increased at 0.3c and maximum pressure difference was observed at a span of 0.95R for all winglet configura- tions. In suction, surface pressure decrease was 10% for all winglet configurations. Keywords : Blade surfaces, Pressure distribution, Wind turbine rotor, Winglets Introduction Wind power potential within India is estimated at 45,000 MW. Although, large wind turbines (capacity, 300 kW-2 MW) are being installed, harnessing wind power through small wind turbines (aero generators: capacity, 400W-15kW; wind speed. 3-10 m/s) for powering homes, hill areas and agricultural farms is still budding in India. Small wind turbine has low efficiency. Adding a winglet on blade tip can improve wind turbine performance. Van Bussel 1 augmented power by increasing tip speed ratio. Jianwen et al 2 used wind turbine with various tip vanes and found increase in power output (2-6%). Pressure distribution of wind turbine blade with tip vane improved pressure difference between pressure and suction surface 3 . Aerodynamic study 4 on wind turbine rotor with winglets showed increase of power production (1.6%). Blade tip modification enhances aerodynamic performance 5 . Winglet added wind turbine rotor blades were tested dynamically and increased power (6.42%) by 25 mph 6 . This study presents pressure distribution along spanwise and chordwise of small wind turbine blade with winglets experimentally to improve performance. Experimental Section Boundary Layer Wind Tunnel (BLWT) BLWT (overall length, 52 m; size of test section, 18.0 m x 2.5 m x 2.15 m; wind speed, 0.5-55 m/s) at CSIR-SERC, Chennai simulates wind flow in a controlled manner to represent flow characteristics in the nature and aerodynamic forces; such a long test section is preferred to achieve natural development of equilibrium boundary layer. Ceiling of test section can be adjusted to obtain a zero pressure gradient. Test section has two turntables: i) upstream side, where studies on models for uniform flow conditions are being carried out; and ii) downstream to conduct experiments under simulated atmospheric wind. Wind Turbine Rotor Models Five rotor models (diam, 340 mm; hub diam, 20 mm; blade length, 140 mm) were fabricated using aluminium. NACA 4412 profile was used from blade root to tip and the same profile maintained for different winglet configurations. Winglet curvature radius and winglet height effects are more dominant compared to other winglet parameters 4 (sweep angle, cant angle, toe angle and twist angle). Winglet models (W1, W2, W3 and W4) were fabricated with different winglet height (% rotor radius) and curvature radius (% winglet height), respectively as follows: W1, 2, 12.5; W2, 2, 25; W3, 4,