# Vortex Formation

1. Aug 16, 2009

### RohansK

1. Can anyone please explain in detail How a Vortex if formed.

I mean what are the reasons and physical phenomena that cause the water entering a bath tub sink to gain a CIRCULAR ROTATIONAL motion and form a Vortex. How do the water molecules otherwise travelling straight towards the sink suddenly form a circular path of motion.

What I want to understand is that how does this TURNING happen. And also explain about the pressure differences created and velocities in the vortex.

2. And why does a bullet gain more velocity when it is spinned along the grooves made inside the barrel, i mean how does the velocity increase because of the rotation.

Please try to be detailed and elaborate it will help to understand better. Expecting a lot from this forum and experts here. This is my very first question here guys , so just help me out.

2. Aug 16, 2009

### fleem

I can't give you a detailed explanation for the vortex, but a bullet does not "gain velocity" because of the rifling. The rifling causes the bullet to stay pointed forward so that it won't lose as much velocity from air resistance, and also so it won't veer off target as much.

3. Aug 16, 2009

### sandoko

hmmm, hi, it is by chance that I stumble upon this thread discussing about vortex and I am planning to do a project in vortex as my mini project. As I am still a first year undergraduate student, I cannot do much but only to investigate the dependence between the radius of the hole and and the length of the vortex experimentally. do you guys have any more interesting idea on what to investigate ?

But when I looked at the question above, i realized that I have not understand the concept behind them yet. The part that I am curious about is how the rotating motion of the fluid just come out to play compared to the initial condition when the fluid is just almost calm. need someone who knows more to enlighten me!!!

but about the formation of the vortex path, my opinion is: as the water rotates(which I haven't figured out the reason ), the part of water that is located nearer to the center rotates with a tangential velocity that is bigger than the part located further from the circle. and as bernoulli equation suggested, the pressure become lower in the center and the air start to be sucked in to the center and there come the vortex.
I am not so sure yet about this explanation as I have not confirmed it from any reference textbook.(sorry for the wrong answer if it is the case, thx)

4. Aug 16, 2009

### Turv

When the water discharges into the plug it creates a vacuum this makes the water increase velocity and creates centripetal spin, when the water gets to a certain level the total pressure is more than the static pressure of the water which in turn sucks faster than the static pressure can maintain resulting in negative velocity pressure (suction). The vena contracta will form on the discharge resulting in a steady flow, also i would like to say this too, any one using the bernoulli equations are getting things wrong, Bernoulli is regarded as a joke with the people i speak too.

Last edited: Aug 16, 2009
5. Aug 16, 2009

### sandoko

ow I see, thanks for your answer particularly on the flaw of bernoulli part.But can you explain it further, particularly on the centripetal spin, and the total pressure part.
and when you wrote about total pressure, can you elaborate it further on who are contributing to the total pressure term??
and can you any suggestion on any reference website or book, or maybe free ebook out there explaining on vortex?
btw, thanks for you enlightening answer.haha. need to brush up my concept more.

6. Aug 20, 2009

### RohansK

Thanks for the response guys.

But yet my question remains unanswered.

In response to what Turv said

When you speak about the Cenirfugal Spin ---- This is exactly what I want to figure out ,
How is this Spin or change in direction to form a rotational flow is initiated. What causes this rotation?

What iis the meaning of the Certain Level stated? And can anyone please explain the static pressure ebing less than the total pressure and how it creates the sucking action and vacuum?

Also can someone shed some light on how and why is Bernoulli wrong tot he extent of being a Joke!!

Members Please do make an effort to explain thi s Vortex concept, its troubling me a lot since many days. Please clear my doubts and let me get the correct fundamental of this phenomena.
This will be great help