Vortex Formation and Shedding
The ocean is over 800 times denser than air which allows significant energy extraction from relatively small motions. From the smallest fish to the largest whale they all use the same mechanism for motion. The body starts forming a vortex by curving itself. This vortex is then passed down the body towards the tail. As the animal straightens out the body they 'push' against the formed vortex and propel themselves forward. Curving the body once again will cause another vortex to form on the other side which creates the von Kármán street. The tail acts to separate the counter rotating vortices allowing even more energy to be transmitted to the animal
The Vortex Power Drive reverses this action. With the ocean current flowing against this stationary bluff body it is forced around the curved edges. This action causes a vortex to form. Once the vortex forms, pressure differentials now cause the Drive to swing into the newly created area of low pressure. Since the fluid is constantly flowing past the Drive the vortex continues past the trailing edge of the Drive. With the new orientation into the fluid flow another vortex will form on the opposite side causing the Drive to now swing into this newly formed area of low pressure.
The Vortex Power Drive rotates around a center shaft, free to orientate itself into any flow direction. The Drive is open to the sea water, allowing the water to fill up the insides of the drive, preventing buoyancy from becoming a force to overcome. Filling specific areas within the Drive with buoyant materials allows the Drive to remain neutrally buoyant while maintaining a large mass. In this configuration the Drive's rotation impacts significant torque on the drive shaft.Version 3.1 Vortex Power Drive with drive shaft at leading edge.
Using the well understood action of vortex formation and shedding to impact movement upon a benign bluff body like the Vortex Power Drive has several immediate operational benefits. The first and most obvious is the lack of rotational blades or vanes. In a world filled with creatures great and small the ocean's life is everywhere. In quick flowing fluids the ability of a large mass like a great fish or mammal to identify a rotating blade as being dangerous is impossible. Damage to a blade or vane on a submerged 'wind' turbine would, in all likelihood, kill the animal unfortunate enough to impact it but would also require expensive repairs to a now inoperational device.
The Vortex Power Drive has a significant presence in the ocean. A typical Drive would be three meters wide and deep. It would fill the entire usable water column. Heights of ten or more meters would be common. The typical installation would group ten or more Drives wide by ten or more Drives deep, amalgamating the energy extraction like typical solar installations. Each Drive rotates about the axis approximately 100 to 120 degrees every one to three seconds. A power plant extracting energy from ocean currents using the Vortex Power Drive would be, by its very nature, a large benign structure.
Placing large man made structures into the ocean requires specialized building methods and materials. Borrowing from the off-shore oil and gas industry the Drives would be built and housed in platform like structures. Utilizing typical building techniques and materials the platforms would stay in place for 20 years or more.
Separating energy extraction from energy generation allows the energy generation to be placed above the water. Connecting each array of 100 or more Drives to a single generation hub reduces development costs substantially. The current industry model of marring a single energy extracting mechanism with a dedicated custom built generation device is not sustainable without significant government tariff programs.
The expected energy generation from a single array of 100 Drives in a 2 m/s (6 fps) flow would be 0.5 to 2 MW depending on the operational depth of the ocean current. A 65 MW field of arrays would occupy an area less than a square kilometer.
Targeting ocean currents flowing between 0.5 m/s (1 foot per second) up to 3 or 4 m/s ( 9 to 13 fps) the supporting superstructure for the Drives are not exposed to the high flow stresses typically seen in tidal currents whose flows can exceed 7 m/s (23 fps).
Keeping the placement of the Drives out of high flow areas works to keep the development costs low and extends the operational lifespan for the superstructures. This has a positive implication on ongoing operational costs while expanding the range of potential development sites to most ocean currents worldwide.
Biomimicry has further advantages when the Drives are placed at specific distances from one another. Like schools of fish swimming in tight formations, each benefiting from the vortexes of the previous, the Drives motion, and therefor energy extraction, can be enhanced through the use of the vortexes generated by the Drive in front of it.