In particular, an easy case where you know you can get away without computing anything is, of course, if your vector field is tangent to the surface because then you know that there is no flux.

特别地，有一种简单的情况，是不用计算的，当向量场与曲面相切，没有通量。

youdao

That is a vector field in which the trajectories are going to be circles centered in the z-axis and our vector field is just going to be tangent to each of these circles.

这是一个向量场，其中旋转轨道是，以z轴为圆心的圆周，并且这个向量场与每个圆相切。

youdao