ducted blade

例句：

1. 1. The ducted blades of the fan are designed to direct airflow efficiently.
   风扇的导管叶片设计用来有效地引导空气流动。
2. 2. The engineer used a ducted blade to cool the engine in a high-altitude test.
   工程师使用导管叶片在高海拔测试中冷却发动机。
3. 3. The ducted blades on the helicopter's rotor were designed to reduce noise and improve efficiency.
   直升机转子上的导管叶片被设计来减少噪音和提高效率。