Gorlov helical turbine
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The Gorlov helical turbine evolved from the Darrieus turbine design, which was altered to have helical blades/foils. Its inventor, Professor Alexander M. Gorlov of the Northeastern University, primarily intended it as a water turbine[citation needed], however it is also somewhat useful as a low tip-speed wind turbine.
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[edit] Fluid Performance
The term "foil" is used to describe the shape of the blade cross-section at a given point, with no distinction for the type of fluid, (thus referring to either a "airfoil" or "hydrofoil"). In the helical design, the blades are twisted about the axis, so that there is always a foil section at every possible angle of attack, including one at an optimal angle to generate lift. The helical design has the effect of evenly distributing the foil sections throughout the rotation cycle. In this way, the sum of the lift and drag forces on each blade do not change abruptly with rotation angle. The turbine generates a smoother torque curve, with minimal torque ripple. Thus there is much less vibration and noise, than in the Darrieus design. It also minimizes peak stresses in the structure and materials, and facilitates self-starting of the turbine. In testing environments the GHT has been observed to have up to 35% efficiency in energy capture.
[edit] Turbine axis-orientation
The main difference between the Gorlov helical turbine and conventional turbines is the orientation of the axis in relation to current flow. The GHT is a vertical-axis turbine which means the axis is positioned perpendicular to current flow, whereas traditional turbines are horizontal-axis turbines which means the axis is positioned parallel to the flow of the current. Fluid flows, such as wind, will naturally change direction, however they will still remain parallel to the ground. So in all vertical-axis turbines, the flow remains perpendicular to the axis, regardless of the flow direction, and the turbines always rotate in the same direction. This is one of the main advantages of vertical-axis turbines.
. The GHT operates under a lift-based concept (see airfoil). This means that it uses forces in the current to "push" and "pull" itself through rotation. The foils of a Gorlov Helical Turbine are shaped like those of an airplane wing and thusly uses the same principles to generate lift.
[edit] Environmental effects
Hydropower is a leading source of renewable energy, and is often very cost effective. A GHT is ideally suited to harness hydropower from small rivers, where the vertical drop is minimal, or when construction of a dam is undesirable, and as such is an example of Damless hydro technology, which may have significant cost and environmental benefits over dam-based hydro systems.
These factors are especially significant for low-power, low-head micro hydropower installations, for which a cost-benefit analysis would likely show that dam construction is not justified for many small projects.
In general, a major ecological issue with hydropower installations is their actual and perceived risk to aquatic life. The GHT is still a relatively new invention, however it may turn out to be one of the more ecologically benign solutions for hydropower, in part because it is claimed that a GHT spins slowly enough that a fish can see it and avoid it. Furthermore, even if a fish swims directly through the turbine, preliminary evidence suggests that a fish will not be harmed. It is theoretically impossible for a fish to become lodged or stuck in the turbine, because the open spaces between the blades are much larger than the size of even the largest fish living in a small river. A fish also would not be tumbled around in a vortex, because the GHT does not significantly alter the overall current flow, so the fish would be harmlessly swept through with the current. At any rate, sensors could be installed to remotely signal an alarm if the turbine stops, slows or is impacted for any reason, such as jamming by a tree branch. Data can be collected and analyzed to assist with aquatic surveys and studies.
This ecological issue is very similar to the issue of avian (bird) deaths in relation to wind turbines, a concern that was frequently raised in the 1990s when modern wind turbines were deployed in increasing numbers. Eventually, the results of scientific studies concluded that as long as turbines weren't located in the path of major migration routes, wildlife fatalities were relatively few. Actually, it was discovered that far more birds died as a result of flying into buildings (e.g. closed windows that must have appeared to the bird to be open). For the GHT, similar studies are likely to set upper and lower bounds on the risk to aquatic wildlife. These estimates can then be compared with other energy technologies in order to find the best energy solutions.
[edit] Systems
Some air turbines presently on the market are Gorlov turbines, such as the Turby wind turbine and the Quietrevolution wind turbine.
[edit] See also
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- US6,253,700 Method for maintaining flotation using a helical turbine assembly
