During oil production, pumping rod is eccentric in the long oil tube, in which flow of the swabbed fluid can be regarded as an unsteady flow of second-order fl.

• 在采油过程中，由于油井较深的缘故，抽油杆在油管中是处于偏心位置的，可以把聚驱井抽汲液在井筒中的流动视为二阶流体在内管做轴向往复运动的偏心环空中的非定常流动。