FORWARD LOOKING STATEMENT

The Hanna Wave Energy Turbine Generator

US provisional patent filed August 2010, Utility Patent application filed August 2011

   I.  Problem to be solved

  To improve the effectiveness of wave energy harvesting and double the electrical output of existing wave energy conversion devices, the technology needs a more efficient air turbine: The Hanna Turbine offers a powerful unidirectional turbine designed to operate seamlessly in the bi-directional air flow environment common to all Oscillating Water/Air Column systems.

  Background

  Wave Energy Conversion (WEC) is an emerging technology that harvests energy from ocean waves. One sub-class of WEC technology uses special turbines to generate electricity.  Although there are different turbine designs in development, they all share a common challenge: Oscillating Water Column (OWC) devices convert wave motion into alternating expansion and compression cycles within an enclosed air duct. The air flow inside the duct can be compared to inhaling and exhaling.  This reciprocating air movement is used to spin a turbine.  The challenge lies in how to spin the turbine continuously in only one direction while the air stream is moving back and forth.

  Three turbine designs currently in use include: (1) Impulse turbines which show promising efficiency coefficients and are relatively inexpensive to manufacture.  Research from 2009 (V. Jayashankar, M. Takao, T. Setoguchi, et al.) favors a twin impulse turbine topology, and (2) Variable pitch axial turbines like the Denniss-Auld Turbine which rely on complex movable blades to adapt to the reversing flow every cycle, and (3) the pioneering Wells Turbine. While the Wells Turbine does spin in one direction, it is inefficient and has numerous weaknesses: it stalls easily, has issues with low-speed operation, has a small operating window, and is difficult to self-start under many conditions.

  WEC device developers have been shifting to the Wells to avoid cost and complexity issues associated with the variable pitch turbines as used by Australia's Oceanlinx. As a result, a great deal of technology development has gone into attempting to enhance and improve the operation of the Wells, including a large body of work from Japan and India. While it is conceivable that continued investment into Wells refinement might garner a modest improvement in efficiency and operating window, the Hanna Turbine shows potential for significant cost reductions and efficiency improvements over the Wells.

II. Scientific and Technical Approach - The Hanna Turbine

 
  A. Concept and Principle of Operation

  Two sets of back-to-back turbine rotors are connected to a primary drive shaft. A precision clutch mechanism in each rotor hub allows the turbine to transmit torque during the power stroke and freewheel during the coast mode. The complete Hanna Turbine system has both turbine sets, with mirrored blade configurations, connected to the same common shaft. In this ideation, the shaft will always be turning in one direction regardless of airflow direction.  One of the two turbine rotors will be in a power stroke while the other is in a coast mode.

  Originally conceived and described by John Hanna in 2010, the Hanna Turbine (HT) shares some attributes with both the Wells and a ducted impulse turbine. Like the Wells, the HT involves a unique airfoil shape. However, unlike the Wells, the HT airfoil is not symmetric. The HT airfoil responds differently depending on the direction of flow in the oscillating air column. When air flow is impinging on the blades' leading edges, the blades (and only one of the two rotors) are in a power stroke or "drive mode". The blades' aerodynamics are tuned to maximize energy harnessed from the incoming airflow. When the flow reverses and air is now impinging on the trailing edges, the "drive" rotor now switches over to a "coast mode " and the other rotor switches over to be the "drive" rotor.  The reverse flow aerodynamics of the blades do not cause either of the dual turbine rotors to reverse direction as would happen on a conventional axial flow turbine. Instead, the blades continue to generate a small amount of torque in the same direction as the power stroke.  The rotating mass of the dual rotors' annular (diffuser) rings function as flywheels and therefore, will also contribute to the angular (spinning) momentum of whichever rotor happens to be in the freewheeling mode.

This arrangement offers several benefits compared to other OWC turbines:

    1. The turbines don't lose angular momentum or inertia during the coast phase.

    2. Generator speed is not adversely affected because the drive shaft has a sustained

        torque value regardless of airflow direction.

    3. The HT powers two generators which are placed outside of the turbine air chamber
        where they can operate in a dry work space and are easier to service and maintain.

    4. There is only a single shaft driving the dual generators. This avoids complex drives,
        transmissions, and gearing.

    5. The energy transfer to the shaft is smoother compared with the more binary power output

        as seen with other turbine designs.

     B. Multiple Applications

  The dual rotors are designed to reside completely inside a sealed air duct.  No turbine or generator components will be immersed in seawater.  The twin rotors turn a common axle which extends outside of the sealed enclosure spinning the two external generators.   The generators, inverters and transformer are all placed within a dry and easily accessible, weather proof utility vault. This advantage is unique to the Hanna system - no other developer can make this claim.  The HT is scaleable and can be utilized in a number of applications such as multiple shore-based jetty-mounted pre-cast concrete modules, or as monolithic cast in place structures built into an excavated sea shore cliff.

  Near and off shore applications could be large power generating OWC buoy farms, wave and wind harvesting vessels or smaller self-powered navigational buoys (similar to those invented by Yoshio Masuda in Japanese waters).  Hanna Turbines could be built onto the legs of off shore oil platforms or built into deep water docking facilities and floating production, storing, and offloading (FPSO) vessels.

  A small, semi-submersible gateway buoy using the Hanna Fractional Turbine (HFT) could provide low wattage power for remote, free-floating or self-propelled buoys. The system's design would allow the turbine to generate electricity even in low sea states.  An HFT gateway buoy promises superior delivery advantages over complex and expensive hydrogen fuel cells or  marginal photovoltaic systems.  A one foot diameter turbine could operate as a primary power source for servo-powered maneuvering.  A smaller 6-inch turbine could provide persistent charging backup for battery-powered components.  Multiple applications will serve the commercial and scientific sectors.  It could provide months of maintenance-free, reliable power for oceanographic monitoring, Iridium satellite links or FreeWave radio transceivers.  Its fully encapsulated, closed-loop, reciprocating air supply will function with low noise levels.  The proprietary air supply mechanism is self contained; there are no intake or exhaust ports to take on water.  All turbine, generating and power-conditioning components will be sealed to operate within a dry, corrosion-free environment. Click HERE for more details.

C. Energy extraction efficiency

 The two spinning rotors are the only moving parts in the entire turbine system.  Non-moving subsystem elements such as pneumatic turbulators will be used to delay flow separation in the boundary layer of the blades. The turbulators enhance lift and reduce aerodynamic stalling without the need for variable pitch blades. Another innovative method to improve the turbine's efficiency is the use of slots along the trailing edges of the hollow turbine blades.  The slots slant high velocity air downwards, serving the same function as aircraft wing flaps used to avoid stalling and raise the lift coefficient of an airfoil at low speeds.

  With an aim toward more efficient mechanical energy conversion and high survivability, the HT will take advantage of robust, light weight plastic and carbon fiber technologies to streamline the manufacturing process for turbine blades and other rotor components. Low friction hydrostatic and polycrystaline diamond (PCD) bearings will be used. The proprietary airfoil design will be refined using computational fluid dynamics software.

  The OWC wave capture chamber is a key component of the Hanna Turbine's power take-off design.  Seasonal local wave climates will be studied and natural wave resonances will dictate the chamber's architecture.  The capture chamber will be engineered to be an impedance-matched column to attain maximum wave to air energy transfer.  Efficient energy extraction over a large bandwidth of wave frequencies will assure that the Hanna Turbine receives optimal pressure and velocity flowrates.  To protect the turbine from pressure spikes during extreme weather conditions, relief valves and a damping plate will be used.

D. Three versatile models

  Adaptive and versatile power take-off options offer three unique, job-specific Hanna Turbine models to choose from:  #1) The first model is configured as described above which drives two external generators only.  #2) The second option is modified to become a self-contained, stand alone power plant where the peripheral rings in both rotors have magnets that induce current into surrounding coils (see drawing at bottom of page).  This model will not use external generators.  This configuration allows the HT to be placed within a straight intake duct that can be orientated either horizontally or vertically.  #3) The third option allows the HT to generate power both internally and externally.  This hybrid model will provide internal power for grid connectivity and two external generators will be relativistic (Homopolar) dynamos that will produce high amperage power to run seawater reverse osmosis desalination plants or other high energy industrial processes.

E. Conclusion

  In-house proof of concept evaluations have been successfully completed.  The Hanna Turbine is an uncomplicated design with only two moving parts.  It offers long-term survivability for decades of low maintenance service. The unique dual rotor configuration can drive two generators, effectively doubling electrical output. The HT is essentially two distinct axial turbines that will extract more energy from a given flow direction of the OWC. This is accomplished without the need for complex and expensive variable pitch or counter-rotating blade mechanisms. The HT can be deployed anywhere in the world as long as a suitable wave climate exists. Environmental studies for similar WEC devices now in place, have all resulted in "Findings Of No Significant Impact".  No commercial fisheries will be effected.

  The Hanna Turbine was conceived to develop a self-rectifying turbine that overcomes the shortfalls found in the 30 year old Wells Turbine design.  This new turbine design promises to be a more powerful, more efficient and less expensive alternative to shore-based OWC systems such as Scotland's Voith Hydro Wavegen device.  Despite the fact that OWC systems have been around for decades, it is still considered to be an emerging technology.  Its present status can be compared to the fledgling wind turbine industry twenty years ago.  A new era for extracting the limitless power from ocean waves now begins.

  Three utility-grade turbine models will be offered as complete, grid-ready packages.  The civil engineering, permitting and construction will be done by the utility or government agency that has acquired a Hanna Turbine system.  Construction plans will use a pre-determined anchor bolt layout so the Hanna Turbine can simply bolt into place.  The client/owner will be purchasing a turnkey, off-the-shelf package that includes everything needed to make clean, renewable energy for decades.

  The smaller, Hanna Fractional Turbine (HFT), will also be developed as an off-the-shelf package to power compact station-keeping buoys for oceanographic research and tsunami warning.

 TORQUE IS THE ANSWER... Doesn't Matter What The Question Is.

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