Salient White Elephant

March 12, 2009

Radially Displaced Darrieus Rotor

This post describes an idea for an extremely large Darrieus Wind Turbine.

Imagine a lattice tower supported by two guy wires:

Lattice Tower with Two Guy Wires

Now add two more towers, each supported by two guy wires:

Three Lattice Towers Each Supported by Two Guy Wires

Now connect the tops of the towers with I-beams:

Lattice Towers and Connecting I-Beams

Now put a ring on top that can rotate with respect to the towers:

Lattice Towers With Ring On Top

Connect the ring to a vertical “torque tube” that is centered about the axis of rotation:

Lattice Towers, Ring, and Torque Tube

Now put a rotating ring near the bottom and add a couple of Darrieus blades:

Radially Displaced Darrieus Wind Turbine

The following diagram gives the general idea for synchronizing the rotating rings:

Synchronizing Rings and Torque Tube

Here’s another way to synchronize the rings:

Synchronizing Rings

Actually, I wonder if the gearbox would even be necessary in the above diagram. If the radius of the rings is large enough, then perhaps this could be a direct drive machine.

The diagrams above depict a two bladed Darrieus. A better design would have three blades in order to provide a relatively smooth power output.

Exceeding the Betz Limit

One of the disadvantages of a Darrieus turbine is that it typically extracts less energy from the wind than a horizontal axis turbine with the same swept area. However, consider a radially displaced Darrieus rotor with an extremely large radial displacement (i.e., the diameter of the rotating rings is very large). In this case the de-energized air will be re-energized by the time it reaches the downwind blade. Horizontal axis wind turbines are typically spaced two or three rotor diameters apart in order to allow the wind to be re-energized as it travels from one turbine to the next. If we make the radial displacement of the radially displaced Darrieus rotor blades equal to this distance, then this should be sufficient for allowing the wind to be re-energized as it travels from the upwind blade to the downwind blade. In this case, the Betz limit says that we should be able to extract a maximum of 2 x 60% = 120% of the wind’s kinetic energy. For this reason, a radially displaced Darrieus rotor should realize a much higher efficiency than a horizontal axis turbine with the same swept area.

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2 Comments »

  1. The guy wires on this would vibrate terribly, robbing power, adding wear tear and noise

    Comment by Pat — March 15, 2009 @ 11:52 am

    • Really? Why would they vibrate more than on the traditional Darrieus? In fact, it seems the provision of multiple towers connected with I-beams would make for even smaller guy wire loads (as compared to the traditional design).

      Comment by Salient White Elephant — March 15, 2009 @ 12:07 pm


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