Shooting water like a laser
Axisymmetric laminar flow (ALF) devices generate streams of water with all the water particles having the same flow rate and direction, much like photons in a laser. They look like glass parabolas of water that seem to hang in the air. Observers really can't tell the arcs contain moving water until the flow is switched off. Then they can watch the well-defined tail of the curve chase the hoop of water back into the fountain. Some devices quickly turn on and off, creating 2 or 3 ft of curved water that follows a parabolic path back into the fountain.
Mark Fuller, founder of WET Deign, studied ALF and wrote his undergraduate civil-engineering thesis on the subject at Stanford University. He later went on to feature ALF in Leapfrog, a fountain he designed while working at Disney's Epcot Center.
"We use traditional pumps to pressurize the water, but then send it through a series of chambers, straighteners, and baffles to line up the flow and bring it all to the same speed. Then it leaves the nozzle," says Tony Freitas, a WET Design engineer. "Most streams are about a half-inch wide and travel 15 ft, reaching about 15 ft high. And we can do smaller. But it gets more difficult as you make them larger."
Surface tension helps keep them together in an ALF stream. But when a large stream hits the apex of its arch and accelerates downward, different parts of the stream begin traveling at different speeds. This warps and distorts the once coherent flow, breaking it up. "We've done studies with flows several inches wide and they look good, but not perfect," says Freitas. "It is just difficult to scale up. But we're still working on it."
Another Shooter in the arsenal, the MiniShooter, sends water up to 125 ft into the sky. Bellagio has 798 of them. SuperShooters, the top of the line, use holding tanks that stand 12-ft tall, 1 ft in diameter, and hold about 75 gallons. Their air is stored at 200 psi in 60-gallon receivers. When it is released into the tank, the pressure launches a plume 245 ft high through a 2.5-in. nozzle. Bellagio boasts 192 SuperShooters.
"Not all the water goes to 245 ft," points out Freitas. "When we tested the SuperShooters, all the water did go to the apex. But some of it was already coming down, passing through itself, as the last of the water was still going up. We discovered it looks better if pressure declines during the shot. So the top goes to 245 ft and the bottom only goes to 50 ft, making it look more like a standing column of water."
Another problem with SuperShooters involved the huge pressure drop across the air-control valve. It was forming ice in the valve body. "To cure that, we put a pressure plate a few feet upstream to control the pressure drop. The plate drops the pressure in half, then pressure drops again at the nozzle. Fortunately, it doesn't affect the display much."
Another possible solution, he adds, would be to add an air-drying subsystem to the fountain. "Bellagio has such a big air system, we decided not to. But if we were doing it again, we might include dryers."
Shooters and other devices that rely more on air pressure than water pumps save money, energy, and installation costs according to Freitas. "It would take a 300-hp pump to create one 245-ft-high jet, and there are almost 200 SuperShooters at Bellagio. You would need 60,000-hp worth of pumps and the whole system would have to be sized as if it always worked at maximum load. Compressed air, on the other hand, can be stored, letting you size the system for the average load. We run the compressors continuously and bank air for peak moments. So our compressors, standard rotary screw models, occupy one-tenth the space pumps would. And the pipes sending compressed air out to the various Shooters can be much smaller than the pipes that would be needed to carry incompressible water for equivalent jets."
A more conventional special effect is WET Design's Popjets. Using traditional plumbing and pumps, it creates little marbles of water that can rise about 5 ft, still retaining their spherical shapes. A special nozzle and valve quickly release about a tablespoon of water that forms the liquid spheres. "They're great for close-up displays and interactive fountains since they're friendly even to small children."
For more subtle effects and relaxing fountains, WET often deploys WaterSkins and WaterIrises. Waterskin is a thin membrane of water on polished black granite or stone. The water is about an eighth of an inch deep and thins somewhat as it goes over an edge. "It creates a highly reflective surface, but it requires good flow delivery that doesn't disturb the surface, very flat surfaces, and sharp edges. After that, physics does the rest. And while we didn't invent this, it is on our palette, and like all our efforts, we try to take it to a level as near to perfect as we can get."
A WaterIris, in WET terms, is a circular hydraulic jump, and a hydraulic jump is water transitioning from supercritical to subcritical. "More simply, water comes out of a nozzle very fast into a basin," explains Freitas. "When it slows to a certain point, the water suddenly gets thicker. It's like watching a wave washing in and out from the center of the basin. Slowly varying the flow rate makes the transition point change and generates a very soothing sound."
Fog on demandAnother element used in fountains to set the mood is fog created either by atomizing water or adjusting temperature and humidity. To use the first method, WET Design sends water at 2,000 psi and 0.05 gpm through a 0.006-in. nozzle. The water hits a steel pin positioned precisely over the hole's center and bursts into tiny water particles making mist or fog. "In small close-up displays, we might use 30 nozzles," notes Freitas. "Bellagio has 5,000."
The second method usually involves injecting cool nitrogen into a chamber filled with warm, supersaturated air. The water condenses into airborne water droplets, or fog. The nitrogen expands, pushing the fog out into the display. "It's a drier, finer mist than the brute force method," says Freitas. "It also doesn't make floors slippery or leave a residue. This makes it well suited for indoor use. But it does have a consumable, the nitrogen."
| The Grove at L.A.'s Farmer's Market features a WET Design fountain. It was first modeled on VirtualWET, a 3D particle-simulation software package that calculates and displays water forms and lets designers explore options. |
Engineers at Show Fountains use fog for something more palpable than setting a mood. They create giant 'water screens" and project movies on them. At first, they relied on the brute-force method, sending 300-psi water into an angled steel plate. The water would smack into the plate and send a sheet of water droplets straight up. "Later developments refined this plate-deflection method and we now use pumps with far less power to create screens 50 ft high and 100 ft wide," says Show Fountain's Connery. "And for some reason, small screens are more fussy about nozzle openings, angles of deflection, and pump pressure than larger screens, Extra time is always needed to fine-tune the smaller nozzles that create screens 15 to 20 ft tall."
Water screens are most effective when images are projected from the rear and in large formats, such as
70-mm film. "Filmmakers record video specifically for water-screen shows, taking full advantage of the magical appearance of images seemingly bursting out of the surrounding water," says Connery.
| Engineers at Show Fountains designed the Precious Moments Fountain of Angels in Carthage, Mo. It uses 100,000 gallons of water and 235,000 watts of light to showcase over 300 larger-than-life statues, some of which weigh over 1,000 lb. Special effects include foam jets, water castles, candelabra, a mist screen, and even a 75-ft-tall geyser. |
To add pizzazz to fountains, some designers offer clients devices that showcase fire. A relatively simple one, the Fire Tornado from WET, consists of a tube into which air is sent and made to swirl using a blower. "Add gas and an igniter, and you have a fiery tornado whirling in a tube. You can even touch the tube without getting burned," says Freitas.
A more ambitious and unusual device, WetFire, combines fire and water. It has its genesis in a project WET did for a casino outside San Diego. At night, the fountain was to serve as a stage for a drama involving human actors. At one point a campfire was supposed to emerge from a pool of water. "At first, we envisioned a small jet of natural gas or propane bubbling up through the water. It's been used before, including at the volcano in front of the Mirage Casino," says Freitas. "But we found gas burns 'inside' aerated jets of water. You don't just get fire sitting above water. Instead, you get this mysterious combination of fire and water coexisting."
One challenge with fire devices, and it is common to all fountain technology, is that engineers have to find a way to hide the equipment. When they can, WET uses pyroigniters that can be replaced before every performance. Otherwise, they do their best to hide electrical igniters.
"We design highly technical systems that should appear to not use any technology at all," says Freitas. "We want them to see flowing water and beautiful finishes like stainless steel and polished granite, not pipes and igniters, no valves clicking, no computers flashing."