What is a Hydraulic Jump?

Engineers need to be able to predict how water will behave in order to design structures that manage or control it. And fluids don’t always behave the way you’d expect. On this episode of Practical Engineering, we’re talking about one of the most interesting phenomena in open-channel flow: the hydraulic jump.

Writing/Editing/Production: Grady Hillhouse

Tonic and Energy by Elexive is licensed under a Creative Commons Attribution License

This video is sponsored by NordVPN.

[TwisterKidMedia]

We also observe hydraulic jumps in atmospheric science. They often happen downstream of mountain rages when mountain waves break. Super critical flow trapped above an inversion layer can transition to sub critical and cause deep mixing of the boundary layer. This mixing transports high winds to the surface in addition to the turbulence being induced by the terrain. This can lead to intense downslope windstorms also called chinook or fohn winds. Where I work in Wyoming, we often see wave breaks and hydraulic jumps produce damaging wind gusts over 100 mph.

[roccoliuzzi]

I'm a contractor. My current job is replacing a hot tub built into a basement remodel thirty years ago. With no room to bring in a new hot tub I suggested a whirlpool bath, an idea the client accepted. The biggest problem was that the hot tub had no drain, water was pumped into the adjacent shower pan when it needed to be refreshed. To overcome this I built a platform with the drain running between it and the concrete floor, through the shower wall, over the top of the existing shower pan.
I was worried about water velocity because of the 20" head pressure. The drain leaves the tub with 1.5" PVC into a trap then travels at a gentle slope, 1/2" in four feet. As it enters the wall it steps up to 2" then flows out of a 3" shower pan drain with grill that is acting in reverse, water coming out horizontally instead of entering vertically. The volume is very impressive as is the sound. It is dispersed enough that it does not splash excessively, I think the grill helps a lot. I was quite pleased.
Here is what I did not expect. The flow from the 1.5" pipe overwhelms the 2" shower drain. Water depth in the pan gradually increases to about 3", near overflow. Then the most remarkable phenomenon and the reason I write. A tremendous whirlpool is created at the drain, 3" deep 2" diameter. No water goes down the center of the drain. By coincidence I am reading a book "The Science of Leonardo". He would have loved it. With the ceiling light of the shower shining through the turbulence the patterns are stable and clear.
I will cut a rubber washer to insert under the "popup" to reduce the flow. I think that will do the trick. We'll see. Thanks for your excellent videos.

[ChevisPreston]

This channel is absolutely fantastic. I know a lot of what you go over, especially with fluid-dynamics, but you always have some little known information. My favorite was the concrete episode. Keep it up man!

[samsngdevice]

I used this video as reference
with my customers who have issues with flooding basements.
By creating a hydraulic JUMP at the base of the roof's gutter system's down spouts, we achieved sucess by eliminating scour, with out digging a complex underground drain system.
THIS CHANNEL HAS EXTREMELY HIGH QUALITY CONTENT. MY CUSTOMERS ARE DELIGHTED.

[CBOYDRUN]

Absolutely one of the best channels on YouTube!

[DroneConflict]

"I owe me marriage to VPNs"

Okay hold up where is this going

[Jeremy_Fielding]

Very interesting indeed! Thanks for posting.

[daemn]

In the process of researching the failure of the Oroville dam's main spillway in 2017, I read up on the earlier 2009 failure of their River Valve Outlet System, which involved a hydraulic jump. Their RVOS pulls water from the lowest/coldest point of the reservoir where it flows through a tunnel to a point under the dam near the turbine outlets (head pressure at about 300psi), and then can be released through a cone valve into another long tunnel that is joined by water from the turbine outlets (the tailrace). RVOS is designed to maintain minimum flow in the river when the reservoir drops below the turbine inlets and to regulate temperature for fish in the river. Oroville's Hyatt power plant is a pumping power station so the turbine outlets are submerged in their own trailrace which can either flow out into the Thermalito Diversion Pool, or pull water back from it when the turbines run as pumps. The tailrace consists of two 35ft diameter, 2000ft long tunnels. One is fully submerged, the other half full and they're cross joined. RVOS cone valves output into the half full tunnel at *extremely* high pressures and flow rates. Normally it blasts the water onto an angled steel dispersion ring which absorbs the high velocity flow from the valves, to merge it more smoothly with the low velocity flow of the half filled tunnel.

The ring had been damaged due to many years of use so earlier in 2009, they removed it.. (presumably with intent to replace). Then a few months later management thought it would be interesting to conduct a test to open the RVOS valve to 100% to see what effect it would have (1. they'd been told never to run it at 100% due to prior damage 2. design specs said RVOS was never to be operated without dispersion ring). The manually operated control (just a big wheel) for the RVOS cone valve sits in a chamber connected through a long person tunnel up into the inner turbine room, and that chamber is separated from the ring valve outlet by a fully sealed 20ft tall steel wall. That wall was designed to fail with 15ft of head pressure behind it in the unlikely event that the manual control valve failed and let water into that chamber. This wall failure would prevent water from backing up the person tunnel into the turbine room.

So.. 5 people enter the control room, and start to open the RVOS valve up to 100%. At 85% all hell breaks loose. The valves release about 4-5K CFS of water at extremely high velocity into a half filled tunnel, and without the dispersion ring this accelerates the velocity of the water in the tunnel for a few hundred feet. During original design (including extensive small scale testing), they realized that even with the dispersion ring a hydraulic jump could form as high velocity flow meets low, that might reach up to the roof of the tunnel, which could cause a vacuum condition in the tunnel upstream of the jump. So they built in a vent in the roof several hundred feet down the tunnel connected by a large tube running back to another vent in the cone valves outlet chamber. Idea being that if the jump formed between the two vents sealing the tunnel it could still equalize the air pressure on either side of it. But without the dispersion ring in place, the jump moved much further down the tunnel than design called for, and blocked the lower vent. This caused a siphon pump effect back to the valve outlet chamber, eventually causing high enough vacuum that the steel wall designed to hold back 15ft of water, blew out into the tunnel almost taking the 5 people in that chamber with it. Doors further up the man tunnel also failed and debris was sucked down that tunnel pelting the people in the chamber now open to raging water and continuing vacuum. With hurricane force winds coming from the person tunnel through the chamber into the RVOS outlet someone managed to turn off the valve to stop the flow. One person was seriously injured. RVOS was repaired in 2014, and operated again that year when drought conditions dropped the reservoir below the turbine inlets.

[blipco]

Perhaps you could show a study of the dangers of low head dams?

[Beatlefan]

Very enjoyable. No flashing images and loads of crappy music - just the facts and a practical demo. Thankyou!

[Ferelmakina]

Fascinating. I got absorbed into the video and ended up in a calm place (the atmospheric music and friendly manners helped a lot). Thank you grady

[freechalupa]

That hydraulic jump at 3:58 propagates just like a normal shock. This is so cool--I've never seen the analogy with supersonic flow so clearly! Just replace the sound speed with the surface wave velocity. So this really is rocket science!

[nathanwforrest]

Another great video! The only thing I would have added is a little discussion about what the Froude number is in various flow regimes. It would be useful for Civil students and others interested in understanding these things.

[MoonyDrak]

I don't general comment on videos but I wanted to say how much I love how you handle your sponsorship ads. They don't interrupt your videos and are extremely well done and to the point. I even found myself watching them and I am even considering getting VPN just to support you. You sure as hell deserved it.

Thank you and keep up the fantastic work!

[benitollan]

0:12
Right side: Lvl 1 turbulent flow
Left side: Lvl 100 *L A M I N A R   F L O W*

_That's how fluid dynamics works_

[TheMapleDaily]

I will respectfully watch every single ad and like all the videos, I absolutely love your content and you deserve all my support! Thank you for this amazing knowledge and thanks to you I am walking down a Engineering path!

[jkbecker]

Grady the type of guy to make a 100% overlooked phenomenon interesting and accessible.

[Brownie]

I'm a kayaker and I clicked on this video because it reminded me of rapids and whitewater in rivers and then you explained it and even mentioned how we kayakers use this physical phenomenon to have fun! You explained it perfectly! Great video!

[GoldenHat]

normaly I would skip this video because the thumbnail couldn t get my attention but then I realized its a practical engineering video. Good work👍

[deeser]

And yet again, you post a video that makes supposedly complicated and abstract things so easy to understand. Brilliant! don't stop being you and amazing. x