I wanted to start by saying a vortex will not work as efficiently in every tank style nor will it provide a specific coral a large increase in flow. It will move a large body of water using less energy then any other method. I am not suggesting that a power head will not be needed to give extra flow to a specific coral just that instead of trying to create small pockets of turbulent flow it would be more efficient to created a vortex and supplement with a powerhead.
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Little facts provided by Wiki http://www.wikipedia.org/
A whirlpool is a swirling body of water usually produced by ocean tides. The vast majority of whirlpools are not very powerful. More powerful ones are more properly termed maelstroms. Vortex is the proper term for any whirlpool that has a downdraft
A vortex is a spinning, often turbulent, flow of fluid. Any spiral motion with closed streamlines is vortex flow. The motion of the fluid swirling rapidly around a center is called a vortex. The speed and rate of rotation of the fluid are greatest at the center, and decrease progressively with distance from the center.
A gyre is any manner of swirling vortex, particularly large-scale wind and ocean currents.
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or extensional stress. In everyday terms (and for liquids only), viscosity is “thickness”. Thus, water is “thin”, having a lower viscosity,
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This question of using a vortex or gyre is not new just not mainstream in an aquarium. This being said I am not spearheading a change that’s radical but showing an option that is lost in the verbiage of Laminar Flow. The vortex created in a large scale whirlpool is impressive enough to sink ships. Two years ago I was mentioning to Kaptken of wanting to reduce the amount of money I spend running my tank and we hit the usual suspects; lights, heaters and pumps. I had a few Ideas how to reduce my lights electric consumption and I was going to insulate select areas of the tank to hold heat in the winter. (Tank was in the basement and used the heater a lot) However, I was still lacking a way of reducing the cost of the pumps providing flow when Ken recalled a conversation with a vendor about whirlpools.
Whirlpools are created and grow based on the physical attraction on water to its self. Combine this attraction with its low viscosity and a small force can move a mountain of water. There is no more efficient use of energy to return in water movement available to the aquariest. In nature the ocean is a series of gyres. Wind Driven Surface Currents: Gyres Background 
In fact the entire ocean and winds are all forms of gyre. Its truly efficient and where we will be using a small pump to effectively create a vortex, the ones in nature are powered by wind, convection tides, currents, the moon and the earth rotation. (among others)
Example A:
Remember as a kid being in a small above ground pool and yourself or your kids would move around the outside of the pool as fast as you could? As soon as the vortex was strong you would try to stop. You got dragged along didn’t you?
Example B:
Notice as the water gives in to gravity it stretches till finally the bond of the water is overcome by gravity. This works because a water molecule having a positive charge on the side where the hydrogen atoms are and a negative charge on the other side, where the oxygen atom is cause the molecules to attract.
All these water molecules attracting each other mean they tend to clump together. This is why water drops are, in fact, drops! If it wasn’t for some of Earth’s forces, such as gravity, a drop of water would be ball shaped. This is also why a laminar flow is so effective in moving water with less power. Conversely two flow directed into each other to create a chaotic turbulent flow has to overcome this attraction of molecules along with the friction created by water passing over water.
Example C:
http://www.youtube.com/watch?v=vk5Y6dRheFw
i wish we could embed video as this is a cool vortex and at various speeds you see the turbulence that is created on the glass walls as water swirls around the semi square container. This is in line to what we are trying to replicate. Not a tight center eye but a large eye that washes the face of the rock work to bathe corals with food and remove waste.
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Water that is in the corners of a square tank may not flow as fast as it will in the center but the corner will have no less flow in any tank using a directional powerhead with water crashing into the output of another. They both will encounter a buffer zone in the corners. The water in a vortex is traveling at the same speed inside and out but since the water is traveling a shorter distance in the center it appears faster.
To get the dynamic flow in the corner you could aim a powerhead directly into the corner but how many corals make it to the corner and need the flow?
Overall because of the tension of water molecules wanting to hold together they will pull water out of the corner albeit slower then at the center of the vortex. won’t the water that contacts the corner create a chaotic flow area as it crashes into the corner?
Since water in a vortex tend to collect debris at the center in an specific area it allows for easy removal during water changes. To reuse an example used earlier that “sand” will move all around the bottom of the tank in turbulent flow, so will the debris leaving it scattered around the tank.
Science and published marine biologist are a funny thing; rarely will one publish something that will get the author ouster sized and ruin a payday. While some may hint at a new direction it is a painstaking ordeal for it to mainstream. Jocephus mentioned that not everything in nature follows the book and while its great to be versed you have to experience it first hand.
Using the turbulent flow method does creates a random flow that our animals get in nature. While this represent what we may find in nature it is not the exclusive realm that a coral will live or flourish. Is it as chaotic and random on the inside of a reef as it is at the top or outside edge? There are tidal pools that sustain reefs where during low tide some corals are out of the water or in stagnate water for hours. While it is our intent to replicate nature as closely as possible it does not mean there are not more efficient ways to provide the needed flow that corals rely on to remove waste and bring dinner.
There have been some studies that flow may effect the growth of a coral. But what happens when water flowing laminar crosses an object? Turbulence is created. Every rock and coral will add a degree of turbulence. Turbulence is quite beneficial for diffusion and mixing as it helps corals breathe and expel waste. However, it is very inefficient in terms of overall bulk motion. Laminar flow stores and best conserves kinetic energy in the flow. This is why a small pump placed correctly can cause a whirlpool of flow after a few minutes of constructive flow acceleration.
Close:
It takes more equipment and energy to provide true chaotic and turbulent flow that mimics true nature then the benefits of a low energy vortex. Corals need some turbulence to remove debris and provide nutrients. Most of the flow created by raming two powerheads output together is lost in a short distance. You can create the most overall flow by creating a vortex and the turbulence will be created as the laminar flow runs into objects.
Great reads if you have some time
Measuring Turbulent Flow In Reef Tanks
Water Flow is More Important for Corals Than Light, Part V
This applied somewhat and just looked real cool
properties of magnetic vortices
Article??
