Static pressure measurements on a rotating and a non-rotating 2.375 m wind turbine blade. Comparison with 2D calculations

Abstract

Static pressure distributions on a 5.35 m diameter, horizontal axis wind turbine have been measured in the CARDC (China Aerodynamic Research and Development Centre) low speed wind tunnel. The pressure distributions on one of the two blades have also been recorded during non-rotating operation in the FFA-LT1 low speed wind tunnel. By applying the Lanchester-Prandtl lifting line theory, 2D equivalent angles of attack (AOA) for the non-rotating blade (NRB) were calculated for each radial station. Using XFOIL, a 2D airfoil analysis code, pressure distributions were calculated at the 2D AOA from lifting line calculations. The XFOIL pressure distributions were compared with data for the NRB. Good agreement was found, especially at Re numbers exceeding 500 000 at all radial stations but for r/ R = 99%. In order to attain the local AOA at each radial station on the rotating blade (RB), the pressure distributions on the RB were compared with data from the NRB. It is assumed, at AOA below stall, that when the pressure signature around the stagnation point is equal for both the RB and the NRB, then the AOA is the same. Significant difference in C l ( α) between the RB and the NRB were found only at r/ R = 30%. At r/ R = 30%, no drop in C l could be measured on the RB even at high AOA, where the NRB since long had stalled. Derived C l ( α) and C d ( α) for the NRB were used as input to WINRO, a computer program based on blade element/momentum theory (BEM). The RB tip seems to be more lightly loaded than predicted by WINRO at all tip speed ratios.