Wind Technology Discussion
In theory; beside Neo-Aerodynamic there are three families of wind turbines. The Savonius, The Darrieus and the Propeller (HAWT as Horizontal Axel Wind Turbine).
Among them HWAT is the most efficient device to harness kinetic power contain in the wind
Darrieus/HAWT
These are the lift base machines; the aerodynamic principle where the birds and the airplane stay airborne.Most of the calculations are based on swept area and stated at 60% of the energy contains in that swept area.
There are something that do not quite reasonably fit.
- Assuming it takes 60% then the whole area behind the turbine should only has about 1/2 of the wind speed that contains the rest 40% of the energy.
- If that's true then how come 99% of the fluid are let through untouched.
- Specially the HAWT are built on a tower the cited reason is to get more energy. It's true! It does not function well because of the drag, the turbulence cause by affect on the wind when it touches an unpredictable ground/landscape.
- The above image says something of the above. That at any moment; the turbine only harnessing the kinetic power contained on and at the vicinity where the its blade touching the wind; other are untouched. As the result, the trail of these smokes appear as an spiral shape.
- In short: ""wind power was 15 or 20 years ago, with no clearly superior engineering solutions" - Annette von Jouanne - Professor of electrical engineering and computer science at Oregon State University appeared at 2006 by The American Society of Mechanical Engineers
Some notes on Neo-Aerodynamic
- Per square foot of airfoil surface; Neo-Aerodynamic is less efficient comparing to either Darrieus of HAWT; However Neo-Aerodynamic has vast airfoil surface (perhaps 100(s) times)
- Neo-Aerodynamic has the combination of the similar tip speed as of an HAWT (with the same diameter). and the high torque of a Savonius.
- Neo-Aerodynamic has its swept area on a horizontal plane instead of vertical plane as of an HAWT.
Savonius
Among turbines are on the market; perhaps those belong to
this Savonius family are the most look alike.
This is the drag base machine where the ratio of energy
get/set causing by the shape of the wind make side Vs.
the wind break side.In theory a Savonius rotor will have two sides. the wind make side where get the energy following this formula E1=R1 * (V1-V2) ^3 where R1 depend on the size, the media of the fluid and the shape of the vane. V1 is the wind speed and V2 is the speed of the vane.
In order for a Savonius rotor get those energies it has to give up this much E2=R2 * (V1+V2)^3 when the vane turn against the wind on the wind break side.
When we put all together the maximum energy a Savoius rotor can harness is E=E1-E2. which is E=R1 *(V1-V2) ^3 - R2 *(V1+V2)^3.
As you see; the speed (rpm) of a Savonius is more of an liability then the asset. therefore this family of turbine are working at its best when it turns slow. The slower it move the more energy is available for its to harness.