Venturi effect based wind generation?

[SimonMester]

So I have seen a couple promised designs based on the Venturi effect, and while I'm dubious of it's practicality, it did get me thinking, if there is anyone who has tried any kind of draft based wind generation. Obviously it would require complex design, or the right place, but has anyone ever tried here?

[Adriaan Kragten]

So I have seen a couple promised designs based on the Venturi effect, and while I'm dubious of it's practicality, it did get me thinking, if there is anyone who has tried any kind of draft based wind generation. Obviously it would require complex design, or the right place, but has anyone ever tried here?

Several small wind turbines with a venturi around the rotor have been built in The Netherlands. However, the venturi was very small and therefore almost not effective. To get an increase of the mass flow through the rotor, the diameter of the venturi must be at least a factor 2 larger than the diameter of the rotor and the main part of the venturi must lay behind the rotor. This large diameter of the venturi behind the rotor makes that the wind speed of air flow outside the venturi increases which results in decrease of the pressure. Decrease of the pressure at the back side of the venturi results in increase of the pressure difference over the rotor plane and so more wind is sucked into the venturi at the front side. So a wind turbine with a big venturi can have a higher maximum Cp than the Betz coefficient if the rotor radius R is used to calculate the Cp. However, a venturi with a very big diameter is very expensive. So it appears that, if the extra costs of a big venturi are put in a bigger rotor of a normal wind turbine, more power is generated. This is why venturis are not widely used. Another problem is that a big venturi works as a vane and so it isn't possible to turn the rotor out of the wind at high wind speeds.

[SimonMester]

So I have seen a couple promised designs based on the Venturi effect, and while I'm dubious of it's practicality, it did get me thinking, if there is anyone who has tried any kind of draft based wind generation. Obviously it would require complex design, or the right place, but has anyone ever tried here?

Several small wind turbines with a venturi around the rotor have been built in The Netherlands. However, the venturi was very small and therefore almost not effective. To get an increase of the mass flow through the rotor, the diameter of the venturi must be at least a factor 2 larger than the diameter of the rotor and the main part of the venturi must lay behind the rotor. This large diameter of the venturi behind the rotor makes that the wind speed of air flow outside the venturi increases which results in decrease of the pressure. Decrease of the pressure at the back side of the venturi results in increase of the pressure difference over the rotor plane and so more wind is sucked into the venturi at the front side. So a wind turbine with a big venturi can have a higher maximum Cp than the Betz coefficient if the rotor radius R is used to calculate the Cp. However, a venturi with a very big diameter is very expensive. So it appears that, if the extra costs of a big venturi are put in a bigger rotor of a normal wind turbine, more power is generated. This is why venturis are not widely used. Another problem is that a big venturi works as a vane and so it isn't possible to turn the rotor out of the wind at high wind speeds.

Interesting points, do you happen to have any diagrams, just for a bit better understanding? I'm a little bit of a rookie myself.
I saw these primarily installed around ledges, not sure why that helps their fucntion.

[Adriaan Kragten]

In 2015 I have written the report KD 600: "Diffusers for wind turbines". I did this for a Dutch company which had the idea to make a symmetrical diffuser in a building and place a VAWT in the centre of the diffuser. The report wasn't made public because I thought that this was a bad idea. However, the report starts with chapter 1 about the expanding wake of a normal HAWT and chapter 2 about a diffuser for a normal HAWT. So I have made a version of KD 600 with only chapters 1 and 2 and added this as an attachment.

 KD 600 chapter 1 and 2.pdf (215.83 kB - downloaded 42 times.)