Water Fountain Shape

w2raustin · May 31, 2015, 15:15

Can anyone explain the physics behind the shape of the attached water fountain envelope? If the water droplets were just ballistic, I would expect a hyperbolic shape but this envelope curves back in.DS3_5106A.JPG

truffaldino · May 31, 2015, 17:38

Perhaps the reason for that is moving air: water moves air due to non-slip on water surface, and there should be a kind of voricial air motion inside the fontain (ring vortex).

The second possibility is the surface tension which tends to reduce fontain surface area

flotus1 · June 1, 2015, 08:12

Great, fluid dynamics in real life

. I would opt for surface tension.
The surface tension acts in a way trying to reduce the surface area of the interface, which results in the water fountain tightening up towards the bottom.

You could check this hypothesis by widening the gap where water is ejected from the fountain. This increases the inertial forces compared to surface tension effects and the fountain should get a more parabolic shape as you expected.

FMDenaro · June 1, 2015, 08:18

I also think about surface tension...additionally, I see the jet opening in a real laminar way, it is projected to avoid developing turbulence

May 31, 2015, 15:15	Water Fountain Shape	#1
w2raustin New Member Bill Rienstra Join Date: May 2015 Posts: 1 Rep Power: 0	Can anyone explain the physics behind the shape of the attached water fountain envelope? If the water droplets were just ballistic, I would expect a hyperbolic shape but this envelope curves back in.DS3_5106A.JPG

May 31, 2015, 17:38		#2
truffaldino Senior Member Join Date: Jan 2011 Posts: 249 Blog Entries: 5 Rep Power: 17	Perhaps the reason for that is moving air: water moves air due to non-slip on water surface, and there should be a kind of voricial air motion inside the fontain (ring vortex). The second possibility is the surface tension which tends to reduce fontain surface area Last edited by truffaldino; May 31, 2015 at 18:39.

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June 1, 2015, 08:12		#3
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	Great, fluid dynamics in real life . I would opt for surface tension. The surface tension acts in a way trying to reduce the surface area of the interface, which results in the water fountain tightening up towards the bottom. You could check this hypothesis by widening the gap where water is ejected from the fountain. This increases the inertial forces compared to surface tension effects and the fountain should get a more parabolic shape as you expected.

June 1, 2015, 08:18		#4
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,768 Rep Power: 71	I also think about surface tension...additionally, I see the jet opening in a real laminar way, it is projected to avoid developing turbulence