Stationary waves on a laminar liquid flow near collision with a surface [duplicate]

Look at the picture below

I know about plateau rayleigh instability. And my opinion is that the reason of this phenomena is plateau rayleigh instability. But there's a question, in the picture above, imagine that we hadn't put any surface on the way of liquid column, then we wouldn't see any of these stationary waves, and the liquid column will continue until it change to drops. BUT, when we put the surface on the way of it, we'll see these waves. and these waves are just seen in the presence of an obstacle.

So, What does the obstacle ( that we put on the way of liquid column to get these waves ) do, that cause these waves?

In short, liquids, because of surface tension at the liquid-gas interphase, tend to minimize their surface area. A liquid column of volume $V$ always has a larger surface area than $n$ droplets of volume $V/n$.
As it turns out the length at which point the liquid column will start to break up is found by the heuristic: $$\kappa R_0 \approx 0.697$$ where $\kappa$ is the wave number and $R_0$ is the initial radius of the column.