JEC COMPOSITES MAGAZINE - Issue #54 - January 2010 - 37

Small wind turbines Table 2: Design values for experimental models. Preliminary design value Rotor radius [mm] Aerofoil Design lift coefficient Design angle of attack [°] Linearization point 1 [%] Linearization point 2 [%] 300 CLARK Y 1.1 8 75 95 Fig. 1: Experimental blades, type 202 and 204. Fig. 2: Experimental blades, type 502 and 504. Design values for each blade Blade type No. Number of blades Design tip speed ratio Blade pitch angle at 80% from root [°] Tip chord length of tapered [mm] Tip chord length of inversely tapered [mm] 202 (Tapered), 204 (Inversely tapered) 5 2 6 1.78 3.4 2.72 2.29 5.6 8.6 11.2 13.4 15.5 64.4 113.3 Fig. 3: Experimental blades, type 302 and 304. Fig. 4: Experimental blades, type 602 and 604 . Blade type No. Number of blades Design tip speed ratio Blade pitch angle at 80% from root [°] Tip chord length of tapered [mm] Tip chord length of inversely tapered [mm] 502 (Tapered), 504 (Inversely tapered) 3 3.4 5.6 40.9 84.0 302 (Tapered), 304 (Inversely tapered) Blade type No. Number of blades Design tip speed ratio Blade pitch angle at 80% from root [°] Tip chord length of tapered [mm] Tip chord length of inversely tapered [mm] 2 5 1.4 3 4 3.7 4 3.4 5.6 22.5 38.0 5 3 7.2 6 2.72 8.6 Blade type No. Number of blades Design tip speed ratio Blade pitch angle at 80% from root [°] Tip chord length of tapered [mm] Tip chord length of inversely tapered [mm] 602 (Tapered), 604 (Inversely tapered) 5 3.4 5.6 24.6 50.4 402 (Tapered), 404 (Inversely tapered) used for our experiment, with wind speed adjustable from 2 m/s to 20 m/s, an induction motor employed as load, and the synchronized frequency controlled by an inverter. For arbitrarily determined frequencies, the corresponding torque and Fig. 5: Experimental blades, rotational speed were type 502 and 504. measured by a torque converter and a revolution counter. The experimental results were used to calculate the power coefficient Cp and the tipspeed ratio in order to obtain the power characteristics for different blade types. Fig. 6 shows the schematic of the experimental apparatus. In the experiments with the 202, 204, 302, 304, 402 and 404 blades, the wind speed in the wind tunnel was set at 4, 6, 8, 10 and 12 m/s and the torque corresponding to the revolution measured by gradually increasing the load. The same procedure was followed for the blades of the 5xx and 6xx types, but their fixed blade numbers are 3 and 5, respectively. Results and discussion 5 4 3.7 6 3.4 4.9 Blade type No. Number of blades Design tip speed ratio 2 6.4 3 5.2 1.1 4 4.5 2.4 18.0 38.0 Comparison of blades with identical design tip-speed ratio The torque and power coefficients of the tapered blades and the power coefficient of the inversely tapered blades, at a wind speed of 10 m/s and the design tip-speed ratio λ=3.4, are shown in Figure 7, 8 and 9 to study the effect of the blade number. The results for the normally tapered blades show that the Blade pitch angle at 80% from root [°] -0.6 Tip chord length of tapered [mm] Tip chord length of inversely tapered [mm] No54 January 2010 / jec composites magazine
JEC COMPOSITES MAGAZINE - Issue #54 - January 2010

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #54 - January 2010
