This shows you the differences between two versions of the page.
Both sides previous revisionPrevious revisionNext revision | Previous revisionLast revisionBoth sides next revision | ||
lab:zephyr:rotors [2016/07/16 06:27] – chrono | lab:zephyr:rotors [2016/07/25 13:46] – [Power Estimation] chrono | ||
---|---|---|---|
Line 1: | Line 1: | ||
====== Rotors ====== | ====== Rotors ====== | ||
- | Compared to drag-only type rotors (Savonius), | + | Compared to drag-only type rotors (Savonius), lift-only type rotors (Darrieus) |
+ | |||
+ | A drag-only type rotor can develop more torque, even at early stages in low wind conditions, but that would require a very specific and resource-intensive generator to accommodate for the very low rotational speed. A typical low end for a direct driven axial flux permanent magnet alternator with many poles is about 100 revolutions per minute. Everything under 100 rpm means huge additional resource investments into rare earth magnets and loads of copper (windings). | ||
+ | |||
===== VAWT Rotor Types ===== | ===== VAWT Rotor Types ===== | ||
Line 84: | Line 88: | ||
^ <x 12> | ^ <x 12> | ||
^ <x 12> | ^ <x 12> | ||
- | ^ <x 12> | + | ^ <x 12> |
**Example: eXperimental Turbine Lenz-Rotor with 0.96 m² surface @ 4 m/s** | **Example: eXperimental Turbine Lenz-Rotor with 0.96 m² surface @ 4 m/s** | ||
Line 119: | Line 123: | ||
| Decent VAWT | 0.30 | | | Decent VAWT | 0.30 | | ||
| Good VAWT | 0.35 | | | Good VAWT | 0.35 | | ||
- | | Superb | + | | Good HAWT | 0.40 | |
- | | Superb | + | | Big Grid MW+ HAWT | 0.45 | |
=== Torque === | === Torque === | ||
Line 150: | Line 154: | ||
To be most efficient, a blade and rotor should be designed to perform near its optimal tip | To be most efficient, a blade and rotor should be designed to perform near its optimal tip | ||
speed ratio at wind speeds it is likely to encounter((Ragheb and Ragheb, Wind Turbines Theory - The Betz Equation and Optimal Rotor Tip Speed Ratio 2011)). | speed ratio at wind speeds it is likely to encounter((Ragheb and Ragheb, Wind Turbines Theory - The Betz Equation and Optimal Rotor Tip Speed Ratio 2011)). | ||
+ | |||
+ | === Reynolds Number === | ||
+ | |||
+ | The Reynolds number range for small-scale gorlov VAWTs is quite | ||
+ | low. In comparison, the Reynolds number operating regime of most airfoils used for aircrafts ranges from **6.3e6 for a small Cessna** to **2.0e9 for a Boeing 747**. | ||
+ | |||
+ | <x 20> | ||
+ | Re = {{V ∗ D ∗ \rho}/ | ||
+ | </x> | ||
+ | |||
+ | ^ Parameter ^ Unit ^ Detail ^ | ||
+ | ^ <x 12> | ||
+ | ^ <x 12> | ||
+ | ^ <x 12> | ||
+ | ^ <x 12> | ||
+ | |||
+ | **Example: Helical Gorlov-Rotor with 35 cm radius @ 4 m/s** | ||
+ | |||
+ | <x 16> | ||
+ | {{4 ∗ 0.7 ∗ 1.225}/ | ||
+ | </ | ||
- | You can watch these calculations in action, applied to reference wind speed measurements on the [[https:// | + | You can watch these calculations in action, applied to reference wind speed measurements on the [[https:// |
- | A tuned VAWT probably has a best-case efficiency of 40%, while a simple drag-based turbine with no optimization nor special aerodynamics may have an efficiency of about 20%. | + | A tuned VAWT probably has a best-case efficiency of 35%, while a simple drag-based turbine with no optimization nor special aerodynamics may have an efficiency of about 20%. |
{{tag> | {{tag> |