本研究探討具翼緣擴散外罩及扭轉葉片對小型水平軸風力發電機之空氣動力特性影響，首先，以數值模擬軟體FLUENT探討翼緣擴散外罩在流場中之效應，結果顯示在外罩內部有加速性，這是因擴散角度與翼緣長度成線性比例的關係。再來以風洞實驗有無外罩、有無扭轉角度葉片及在不同風速與不同葉片數(solidities)下進行實驗。本論文為研究翼緣擴散外罩以及扭轉效應對功率、扭力輸出和風力發電機轉子之旋轉速度在高速(10~20米/秒)的實驗。而翼緣擴散外罩入口直徑為30公分、長度為10公分、擴散角度為30度、翼緣長度為3公分以及扭轉35度之扭轉葉片。結果顯示，設計出前緣擴散外罩可顯著的提升功率輸出、扭力輸出、小型風力發電機轉子之旋轉速度以及功率係數可能超過貝茲限制。翼緣擴散效應對於轉子性能取決於solidity和風速，隨著solidity和風速越大，翼緣擴散效應的影響就越小。功率係數和扭力係數則隨著風速逐漸增加趨於一恆定值，而在solidity為35-40%時有最大之功率輸出。結果也顯示出在不同轉子中，大翼尖扭轉葉片有最高的功率輸出。 This thesis studies the aerodynamic characteristics of a small horizontal-axis wind turbine with twisted blades and a shrouded diffuser with flange. First, a numerical study is conducted using a FLUENT software to investigate the effects of flanged diffusers on flow characteristics. Results show that the flow is accelerated inside the diffuser, which is roughly, linearly proportional to the diffuser angle and the flange length. Second, wind tunnel tests are conducted without and with the flanged diffuser, without and with twisted blade angle, under different wind speeds and blade numbers (solidities). These experiments investigate the flanged diffuser and twisted effects on the power, torque outputs, and rotor rotating speed of wind turbines at high wind speeds (10 to 20 m/s). The flanged diffuser has an inlet diameter of 30 cm, a length of 10 cm, a diffusion angle of 30o and a flange length is 3 cm, and the twisted blade has 35o twisted angle. Results show that the designed flanged diffuser may significantly increase the power output, torque output and rotor rotating speed of the small-size wind turbine, and the power coefficients may exceed the Betz’ limit. The flanged diffuser effect on these rotor performances depends on the solidity and wind speed. The higher the solidity and the wind speed are, the smaller the flanged diffuser effect is. The power coefficient and torque coefficient for the rotor with the flanged diffuser gradually approach constant values as the wind speed increases. Solidities of 35-40% have the maximum power output. The results also show that the twisted, large-tip blade rotor has the highest power output among the tested rotors.