Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It only takes a minute to sign up.
Sign up to join this community
Why does water flowing (falling freely) from a tap become turbulent after some distance?
Radius at tap = 0.4 cm Distance from tap where turbulence start = 15 cm approx Radius where turbulence start is 0.1 cm approx. At this flow the tap fills 10 ml in 5 secs approx.
I tried using Reynolds number...but it is not in the turbulent region .
fluid jets which are laminar and of small diameter get stretched out into thinner jets as they fall, because the head end of the jet is moving faster than the tail which is still attached to the water source.
When the diameter of the jet becomes small enough, something called Rayleigh instability sets in, in which the jet spontaneously breaks up into individual droplets. All it takes is a very tiny perturbation of the jet to trigger this breakup, which results in the jet disintegrating into a falling stream of droplets with a certain size and spacing between successive droplets.
At no time in this process does the flow become turbulent.
The flow does not become turbulent. It is the interplay between gravity and surface tension that causes the break-up into droplets.
Due to gravity, the fluid will accelerate. We know from mass conservation that the cross-sectional area will diminish. You can also see this in the picture.
Surface tension keeps the water as one stream initially. However, further down the stream the surface tension force in the horizontal direction becomes strong, due to the smaller curvature. Surface tension in the vertical direction is much weaker, and hence the flow breaks up in droplets.
