Green Energy & Expo

Biography

Biography: Tesfaye Meseret Abebe

Abstract

The basic principle of a wind turbine which converts wind energy into electricity comes from the lift force produced by the flow of air through the rotor. In this paper the aerodynamic profile of a small scale wind turbine rotor blade is designed based on a surveyed meteorological data for a site location   called (Aysha dawale, ETHIOPIA).  To design this blade the blade element momentum theory (BEM) is used, and based on this theory a code is developed using MATLAB to facilitate the design process.  Types of airfoils which are used in the small scale wind turbine  industry were investigated  and compared  based on optimum aerodynamic  performance  and thickness  to chord ration for structural stability. According to this criterion the NREL airfoil families suited for small scale wind turbine blades in the range 2-5m blade length are selected and simulated using XFOIL to be an input for the design. After deciding the above initial parameter (airfoil type), the essential geometrical parameters such as twist angle and chord distribution along the blade span is optimized. The final values of this parameters decide the amount of power that can extracted from the wind, which is defined by the power coefficient.

An optimum power coefficient result requires optimizing the twist angle and chord distribution. In this design the chord distribution is designed to follow a  linear shape tapering from the root to the tip  of  the  blade.  The  remaining  parameter  (twist  angle)  is  optimized  using  gradient  based optimization technique coupled with the BEM program coded in  MATLAB. This optimization technique is an automated process which receives variables to be optimized from the MATLAB solver (fmincon) and feeds through the BEM code, while the BEM code simultaneously access the simulated  data’s  of  the  airfoils  and  validate  the  optimum  variables  when  a  maximum  power coefficient result is achieved. Based on this design technique a blade is designed for wind speeds which occurs most frequently  weighted  by the weighbull  distribution.  Simulation  results of this design using QBLADE yields a minimum capacity of 1.4KW: at 4m/s wind speed, 50RPM rotor angular  speed  and a maximum  capacity  of  12.8KW:  at  8m/s  wind  speed,  80RPM  rotor  speed efficient wind power conversion capacity is achieved. Further increasing the rotor angular speed to 200RPM increases the power capacity  to  94.3KW  at  16m/s  wind  speed,  but  according  to the wind  speed  distribution   in  the selected region, for an average annual wind speed of 8.3m/s the rotor angular speed should be no more  than  80RPM  for  efficient  power  conversion   purpose. Within  this  bound  the  turbine  can achieve a rated output power of 12.8KW.