Vortex Shedding in Water

Wolfgang uses a pendulum partially immersed in a makeshift flow tank to show us the effect of vortex shedding on a small object.

When fluid flows around a cylindrical object, there is a range of flow velocities for which a von Karman vortex street is formed. The shedding of these vortices imparts a small, periodic force on the object. Here the object is a cylinder attached to a physical pendulum whose frequency of oscillation is adjustable. The end of the cylinder is submerged in flowing water. When the frequency of the pendulum is adjusted to match the frequency of vortex shedding, the cylinder swings transverse to the direction of flow with a peak-to-peak amplitude of a few centimeters.

[NatSciDemos]

Correct, the slower stream would result in a shedding of vortices at a lower frequency. If that frequency is different from the pendulum's, then the pendulum will not be resonantly excited. Furthermore, the velocity of the slower stream might be too slow for the alternate vortex shedding (von Karman vortex street) to occur.

[changenoways]

Can you please explain this to the engineer who designed the shaking lamp post outside my house?

[DungeonMetal]

I love these videos, many thanks to those involved

[qzorn]

nice water clock. 8~) This is great to show how a basic Vortex flow meter sensor reacts to flow and the St: Strouhal

[LogicalYouth]

this is really creative ! I got why the skyscrapers and long chimney are tested for karman street

[jvon]

@2:25 you should stop the pendulum completely. It seemed as though the pendulum once let go started the movement. Or see what happens when the pendulum is already existing prior to weather flow.

[superniceJeffLee]

I think the flow speeds upstream and downstream are the same, along the channel. The flux was constant and the cross-section was also a constant, i.e. this will tell us the flow speed can only be constant. Do you have a aquarium side view? if the water depth in the downstream section was a bit higher than the front section, then the fast-slow claim can be true. Anyway, this is a great video.

[Odyssey-Quotes]

Amazing video,
Is it possible for can you to please share the parts that need to build this vortex shedding,

[hellsjester]

I'm pretty excited that I soon will start a PhD about this phenomenon. :)

[precisionwresonance]

in this design, the cylinder is fixed, and the fluid is flowing into it, but does anything change if the fluid is affixed and the cylinder is the moving part? like a soccer ball traveling through windless air.

[hardeepsingh]

Thats interesting but why pendulum fluctuate more at the end not at the beginning?

[wbeaty]

That dim vertical line on the water, moving slightly.   Edge of a monolayer?   I've seen that effect on slow-flowing sunlit creek beds, caused by skin oils of human legs!

[wujunie]

I wonder if the vortex frequency is similar to the pendulum swing frequency when the swing amplitude is large? Does the pendulum swing frequency be related to the environment in which it is located, in the water and in the air, or in the lower part of the water, as in the video?

[zack_]

How to reconcile the results. At 1st the pendulum swings faster downstream with 'slower' flow rate. At reduced flow rate it swings more slowly ?

[fuelban]

So the slower stream, has a longer interaction with the obstacles surface area {the pendulum} And so has more mechanical affect whilst passing over the surface, very interesting if some what counter intuitive, makes me think, nice 1..thanks, interesting video guy.
Thom in Scotland.

[tylerloconte]

Can this not be utilized to generate energy?

[ritikajain]

Is it possible to construct this entire set up for a group project on vortex shedding?

[JaegerVargen]

Why is the flow speed lower at the downstream location, is it because you have an inclination of the bottom plate (also, I had a hard time seeing any difference in the ping-pong ball test)? If not then I would rather guess that the upstream location is affected by entrance disturbances that destroy the regularity in the pattern.

[osru_]

But is there something more than that?

[lord_of_love_and_thunder]

The vortex structures are mechanistic phenomena that shouldnt change the material properties of the fluid. Why is there a change in the optical behavior due to these structures ? Is it because of underlying impurities in the fluid that get concentrated by the vortices ?