Analysis of low wind speed small hawt using blade element momentum theory

Abstract

BEMT is a fast, simple and fair accurate tool in designing, analysis and optimize aerodynamics of the wind turbine; however there are some problems facing BEMT like tip losses, centrifugal effect to lift and drag coefficients. The aerodynamic performance of a tapered and twisted small horizontal axis wind turbine of blade radius 0.42, which operates at low wind speed, was investigated in this study; by Blade Element Momentum Theory (BEMT) and Wind tunnel testing for validation. A BEMT code was developed to predict the power coefficient (Cp) against tip speed ratio (λ) curves of this turbine at different pitch angles. A model of the same turbine was tested in a UTM-LST Low Speed Wind at three different pitch angles -10°, -5° and 0°, to validate the results of BEMT code. The power of the turbine was calculated through the torque of the rotor shaft measured by a torque sensor. The BEMT code showed good agreement with the experimental results at mid-range tip speed ratio (λ<4) and gives relatively high error at high tip speed ratio. .The study showed that for this turbine, pitch angle gives the best Cp distribution over a wide range of tip speed ratios. A Cp — λ curve with optimized pitch angle was then plotted to help modeling a control pitch angle system.