设<img src="https://static.zxtiku.com/wangke/imgs/topic/3294eb90da88d436c1bcf40a0ab93076.png"/>为曲面<img src="https://static.zxtiku.com/wangke/imgs/topic/0151075759d4a68f2ad16cd5ef987996.png"/>介于平面<img src="https://static.zxtiku.com/wangke/imgs/topic/78b7b004b0bd409c0703b3d8bf5e4ec2.png"/>之间的部分，则流速为<img src="https://static.zxtiku.com/wangke/imgs/topic/6ccaccafe48cfa4512df617ca2052edd.png"/>的流体流过曲面<img src="https://static.zxtiku.com/wangke/imgs/topic/3294eb90da88d436c1bcf40a0ab93076.png"/>下侧的流量为（）．‎