Limited feasibility study of the Wind Energizer (WE) Concept by Leviathan Energy

The WE  promises to increase power output from a wind turbine (WT) as it deflects and “energizes” the flow ahead of the WT, see http://leviathanenergy.com/technology/leviathan-wind/.

Vorcat, Inc. performed a preliminary study that demonstrated the efficacy of the concept. In addition, placing a second WT directly behind another unit was found to be impractical due to strong blockage.

 A sketch of the setup modeled is shown below (wind direction is from right to left):

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The Tasks:

  1. Place two WEs as sketched in a row.

  2. Compute the Available Wind Power Gain (AWPG) in the rotor plane

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where Uz is the streetwise velocity, UZ,0 is the unperturbed axial wind velocity (P is the available wind power).

 

The Grid:

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Closeup of Wind Energizers

Closeup of Wind Energizers

 

Rotor Model   

  • based on GE 1.5 MW turbine:

  • 3 blades per rotor

  • vortons released at tips only

  • induction ratio a = Vi/V∞.

  • For simplicity both rotors are assumed to experience the identical a=1/2.

  • Tip speed ratio (Xtsr) connects blade movement to simulation time. For simplicity Xtsr=10 (normally determined from empirical power coefficient). 

 

Results:

Flow with two-rotors over fully inviscid geometry:

  • Isolates front rotor wake flow contribution to the power drop at rear rotor

  • Serves ONLY as a test case to rotor flow model compared to experimental and/or design parameters.

Flow with 2 rotors over fully inviscid geometry T=10.2

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Available Wind Power Gain (Inviscid Surfaces)

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Results:

Flow of two-rotors including viscous ground surfaces (real-life scenario; only strongest vortons shown)

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Available Wind Power Gain  - Comparison between viscous ground (red) and inviscid ground (blue)

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Comments on Results & Conclusions

  • Flow upstream of WE 1 did not transition to fully turbulent.

  • Loss in power at rear rotor is in large part due to the wake resulting from front rotor.

  • WE increases power at rotor planes (more substantially at rotor 2 where the flow is fully turbulent).

  • Flow tends to recover KE between front and rear rotors and is distance dependent.

  • Results are very sensitive to rotor flow model.

  • Inviscid grid case computes very fast and allows for quick analysis of rotor model. Here: 300K vortons, T=10.5. Grid has 26,352 triangles.

  • Viscous case: Takes about 20X the inviscid case. Grid has 26,352 triangles and 9 layers, equilibrium reached with 5.5M vortons.

 

Recommendations and Future work:

Improve rotor model:

  • Adjust vorticity production at the blades to local transient conditions.

  • Enhance realism of blade modeling (e.g. release vortons along the blades; compute local flow around the blades.)

  • Select rotor parameters that fit specific commercial wind turbines.

Improve flow upstream of WE 1 by devoting more resources to computation of a complete turbulent boundary layer:

  • Higher Reynolds number and finer grid

  • Either incorporate longer plate upstream of WE 1 or force early transition via bump or trip wire.

  • Expand flow region in spanwise direction.

Use enhanced modeling as in 1 and 2 to investigate the effect of the separation between wind energizers on performance.