subsonic boundary layer

例句：

1. 1. The aircraft flewat a subsonic speed.
   飞机以亚音速飞行。
2. 2. The sound of thewaves was so loud that it was almostsubsonic.
   海浪的声音如此响亮，几乎接近亚音速。
3. 3. Thesubsonic boundary layeris where the airflow slows down to a very low speed.
   亚音速边界层是气流速度减慢到非常低的速度的区域。