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--- lab:zephyr:rotors [2016/07/16 12:04] – [Power Estimation] chrono
+++ lab:zephyr:rotors [2016/07/25 13:46] – [Power Estimation] chrono
@@ Line 1: / Line 1: @@
 ====== Rotors ======
-Compared to drag-only type rotors (Savonius), the lift-only type rotors (Darrieus) haven proven to be generally less suitable for low wind environments. However, the maximum speed of drag-only type rotors is always lower than a comparable lift-only type rotor, because a lift-only type rotor can rotate faster than the wind speed at the tips but with less torque. 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).
+Compared to drag-only type rotors (Savonius), lift-only type rotors (Darrieus) have been proven to be generally less suitable for low wind environments since they're difficult to start up. The maximum speed of drag-only type rotors is always lower than a comparable lift-only type rotor, because a lift-only type rotor can rotate faster than the wind speed at the tips but with less torque. However, the Gorlov rotor with a NACA 0015 airfoil may be a very well suited lift-type rotor for small-scale, low wind environments.
+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 =====
@@ Line 84: / Line 88: @@
 ^ <x 12>A</x> | m² | Swept area (turbine/sail etc.) |
 ^ <x 12>V</x> | m/s  | Wind speed |
-^ <x 12>\rho</x> | kg/m³ | (rho) Air density (~1.225) |
+^ <x 12>\rho</x> | kg/m³ | Density of Air (rho) ~1.225 at 25°C |
 **Example: eXperimental Turbine Lenz-Rotor with 0.96 m² surface @ 4 m/s**
@@ Line 119: / Line 123: @@
 | Decent VAWT | 0.30 |
 | Good VAWT | 0.35 |
-| Superb  VAWT | 0.40 |
+| Good HAWT | 0.40 |
-| Superb  HAWT | 0.45 |
+| Big Grid MW+ HAWT | 0.45 |
 === Torque ===
@@ Line 151: / Line 155: @@
 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)).
-=== Reynold Numbers ===
+=== 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}/{\u}}
+Re = {{V ∗ D ∗ \rho}/{\nu}}
 </x>
 ^ Parameter ^ Unit ^ Detail ^
-^ <x 12>V</x> | m/s | incoming flow velocity |
+^ <x 12>V</x> | m/s | Incoming flow velocity |
 ^ <x 12>D</x> | m | Turbine Diameter |
-^ <x 12>\rho</x> | kg/m³ | (rho) Air density (~1.225) |
+^ <x 12>\rho</x> | kg/m³ | Density of Air (rho) ~1.225 at 25°C |
-^ <x 12>\u</x> | m2/s | Kinematic viscosity Air at 25 °C (1.57×10−5) |
+^ <x 12>\nu</x> | m²/s | Kinematic viscosity of Air (nu) ~1.57e-5 at 25 °C |
-**Example: eXperimental Turbine Lenz-Rotor with 0.96 m² surface @ 4 m/s**
+**Example: Helical Gorlov-Rotor with 35 cm radius @ 4 m/s**
 <x 16>
-{{4 ∗ 1 ∗ 1.225}/{0.0000157}} ≈ 312102
+{{4 ∗ 0.7 ∗ 1.225}/{0.0000157}} ≈ 218471
 </x>

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