Explain Turbulence I'm a high school student. I still don't understand what turbulence is. Please can you explain what it really is? This is what I think it is: rotating motion of water when a particle travels at a velocity of $V$.  
 A: Turbulence isn't only about water, it is about fluids in general.Flow can be divided into three types : laminar, transitional and turbulent.The turbulent flow  occurs when the fluid is flowing fast and the laminar when it is flowing slowly.
In laminar flow the motion of the particles of fluid is very orderly with all particles moving in straight lines parallel to the pipe walls. In turbulent flow the particles move in a rotating motion. Actualy, velocity itself is just one of the factors that affect the flow of a fluid, for that a relation between the factors (density, diameter of the pipe and velocity.) is summed up by a the Reynolds number: if it is less than 2300 the flow would be laminar, if it is greater than 4000 the flow would be turbulent and if it is in between the flow is transitional. And here is a simple guide with diagrams: http://www.efm.leeds.ac.uk/CIVE/CIVE1400/Section4/laminar_turbulent.htm
A: To give a definition of turbulence is hard, and every aspect of turbulence is controversial, but there are some essential elements:
Turbulence requires the presence of vorticity.
Turbulent flow has a very complex structure, involving a broad range of space and time scales.
Turbulent flow fields exhibit a high degree of apparent randomness and disorder. However, close inspection often reveals the presence of embedded coherent flow structures.
Turbulence is chaotic.
A: Well for a very elementary definition I would have to say that when the flow of a liquid starts to become unsteady, it is referred to as turbulent flow.
As @tpg2114 says in his comment, it is pretty difficult to explain turbulence here as it is a vast topic. Well i would advice you to study about it further on wikipedia first and then some dedicated books/texts.
Still, to summarise in short, consider the flow of water from a tap, first you open it so less that only drops come out, precisely increase the flow a little more untill a very thin stream of water flows, this is streamline flow, in this flow every droplet of water falls behind another and has same velocity as that one at that point, imagine a marching army. But when you get in frenzy and turn the tap all way open, a strong rush of water flows out in a hurry, imagine rush hour at a very heavily crowded street and as soon as the green lighg goes and everyone starts walking, someone may even fall down, no order, a chaotic flow and an unsteady flow of water is referred to as turbulent flow
Wasn't that short after all, huh !
