Technology - introduction

Venturi Wind BV & Aerolift Patent BV have created a new type of soundless Micro Wind Turbine that is the first MWT accepted in urban areas. On top of this it has an exceptionally high electricity output at inland wind locations and looks nice like a transparent sphere. This will enable entry of the MWT into the billion €market of urban areas and homes that is currently still untouched. The necessity for these MWT’s is underlined by growing objections to present large wind turbines.

Conventional wind turbines have the blades attached to the axle of rotation (the hub) in a cantilevered way.The blades rotate and describe a circular surface, the so-called rotor surface.The rotor extracts energy from the air flowing through this rotor surface and has a theoretical maximum efficiency of 59%, which is known as the Betz law.

Technology - the invention

The blades of the small Venturi turbine are attached to the hub on both ends. When rotating, a sphere is described. Because of its unique aerodynamic behavior, Venturi turbines create a wind flowpattern that converges first, like rapids in a river. Within the sphere, a low-pressure area is generated which attracts the air in front of the rotor towards the sphere. After the rotor has absorbed energy from the air, the energy-poor air is swung radically outwards through the so-called Venturi planes and is carried away by the surrounding airflow.

This causes, in respect to conventional turbines, the air flowing through the turbine and the air surrounding the rotor to be used more effectively, thus resulting into the efficiency of the Venturi turbine being considerably higher than the efficiency of conventional wind turbines.

Wind tunnel measurements at the Technical University of Delft have shown that a three blade Venturi Turbine has a measured efficiency of 85%, which is 40% better than the theoretical maximum efficiency of 59% known as the Betz law.

Venturi effect concept has been patented under nr. WO-0134974 in the USA and Europe (valid until 2019; pending in Japan).

The Advantages of the Venturi turbines are:

• Soundless

The tips of conventional wind turbines are the main noise generators. Compared to this, the sound generated by a small Venturi turbine is virtually non-existent because it does not have such a tip. Also, there is no gearbox and the number of blades reduces the speed of rotation.




• Reduced down time, crucial to non-seaside locations

The six bladed rotor induces a high start up moment. This enables the turbine to run almost continually, unless there is really no wind. The Venturi effect described above enables the Venturi turbine to generate a higher level of power at lower wind speeds, which is essential at a midland wind regime, where most of the applications will be found. This also minimizes the down periods to 10 to 20 % of time where conventional turbines are known to stand still for 50% of time. This results in a more constant power supply to a consuming system or a battery than conventional wind turbines would be able to deliver under the same circumstances. At lower wind speeds the Venturi turbine will potentially generate three times more energy than comparable small wind turbines simply because the Venturi turbine will run and absorb energy from gusts while other wind turbines will require these gusts for their start up. This is of crucial importance for locations that are not at the seaside.




• Attractive design and styling

  Generally, rotors create visual turmoil and apprehension. Because the running small wind turbine is visually associated with a transparent (glass) sphere, this unrest is reduced and is recognized as attractive and pleasing to the eye.

  Therefore the Venturi turbine is an fun object to be placed at locations that are meant to catch the eye, like billboards or attraction park entrances. There needs to be a way to make them extremely quiet under all conditions”, the American Wind Energy Association stated in its Roadmap for small wind turbine technology.

  
  
  
  

• High Reliability

Because the blades of the Venturi turbine are attached to the hub with both ends, the feet of the blade and the flexible blade itself are subjected to non-fluctuating tensile stresses only. Wind gusts and gyroscopic effects barely influence this2. This way of rotor construction therefore is so robust that it practically excludes the breaking of blades. In case a blade would brake, it is still attached to the turbine at its other end. The generator is integrated into the central hub of the Venturi turbine. The magnetic field is induced by permanent magnets. The generator dimensions are matched to the rotor characteristics thus making an expensive and problem prone gearbox obsolete.




• Cost effective

Whist the theoretical background of the blade configuration is very complex, the manufacturing is utterly simple because the blade can be laser cut from plate. Because normally the blades constitute a large part of the cost price because special tooling like a mould is required, the Venturi turbine can be economically produced at relatively low volumes. The cantilevered construction of conventional blades cause the foot of the blade to be subjected to strongly alternating bending moments caused by fluctuating wind gusts and gyroscopic effects. Additionally the unsupported tip end initiates the blade as a whole to vibrate. The alternating stress loads are the main cause of breaking blades.