Fluid Dynamic Wind Turbine Design

In this research a mathematical code based on BEM theory has been developed. The codes based on BEM theory are widely implemented by scientific and industrial community, in order to design Horizontal Axis Wind Turbines and to evaluate their performances.

These numerical codes are 1-D codes characterized by fast processing time and reliable results if numerical criticalities are faced and solved. The criticalities regard the radial flows along the blades, the correct determination of the induction factor, and a correct representation of lift and drag airfoils coefficients.

Dealing, for example, about the radial flows along the blades, it is a 3-D effect, but can be dealt with by a 1-D code using a mathematical expedient. Radial flow along the blades is dealt with by increasing the 2-D airfoil CL distribution in dynamic stall/fully stalled aerodynamic conditions.

This code has been tested and validated for the Phase II wind turbine (S809 airfoil), the Phase VI wind turbine (S809 airfoil) and the RISØ test turbine LM 8.2 (NACA 63x-2xx airfoil series along the blade).

The numerical code developed, is able to evaluate the mechanical power curve of the wind turbine and its power coefficient. The results were compared with the experimental measurements found in the literature.

The numerical code can be implemented to design a new wind turbine, and/or to evaluate the performance of a given wind turbine.

NREL PHASE II

Number of blades	3
Rotor diameter	10.06 m
Rotational speed	71.63 r/min
Cut-in wind speed	6 m/s
Cut-out wind speed	not applicable (stall control)
Rated power	20 kW
Power regulation	Stall
Blade type	Constant chord, no taper no twist
Root extension	0.723 m
Blade pitch	12 degrees (fixed along the blade)
Blade profile	NREL S809
Blade chord	0.4572 m at all span stations
Blade twist	None

Phase II *

Basic machine
parameters and geometry

Comparison between experimental and simulated power.

*C.P. Butterfield, W.P. Musial, G.N. Scott and D.A. Simms: “NREL Combined Experimental Final Report—Phase II” - NREL/TP-442-4807 - August 1992.

NREL PHASE VI

Number of blades	2
Rotor diameter	10.06 m
Rotational speed	72 r/min
Cut-in wind speed	5 m/s
Cut-out wind speed	25 m/s
Rated power	10.0 kW
Power regulation	Stall
Blade type	Variable chord and twist
Root extension	1.258 m
Blade pitch	3 degrees at blade tip
Blade profile	NREL S809

Phase VI test
at NASA AMES
Wind Tunnel *

Basic machine
parameters and geometry

Comparison between experimental and simulated power.

* Courtesy of DOE/NREL, Credit - Warren Gretz.

RISØ test turbine LM 8.2

Number of blades	3
Rotor diameter	19.0 m
Rotational speed	47.50 r/min
Cut-in wind speed	4.5 m/s
Cut-out wind speed	not applicable (stall control)
Rated power	108 kW
Power regulation	Stall
Blade type	Variable chord and twist
Root extension	2.7 m
Blade pitch	0 degrees at blade tip
Blade profile	NACA 63x-2 xx

RISØ test turbine
LM 8.2 - On field measurements*

Basic machine
parameters and geometry

Comparison between experimental and simulated power

* J.G. Schepers, A.J. Brand, A. Bruining, J.M.R. Graham, M.M. Hand, D.G. Infield et al. “Final report of IEA Annex XIV : Field Rotor Aerodynamics” –ECN (Energy research Centre of the Netherlands) Report - ECN-C-97-027 - MAY 1997.

Micro Wind Turbine: design, realization and performance evaluation

Diameter 450 mm; NACA 4415; n=1000 rpm; Variable chord and twist.

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