COMPARATIVE STUDY OF THE AERODYNAMICS OF SEVERAL WIND TURBINES USING FLOW VISUALIZATION

摘要

Improved understanding of three-dimensional, unsteady flows on wind turbines is necessary to aid validation of advanced modelling. In this work, visualization techniques were used to study the flows over three working wind turbine blades having different designs. Tufting was shown to reveal the gross aerodynamic behavior, and inexpensive oil flow tests gave a graphic insight into the average boundary layer behavior. The results were correlated using the PROPPC code. The wind turbines tested included the Enertech 21-5, with and without tip plates, the Carter 25, and the Enertech 44-50. Tip Reynolds numbers ranged between 500,000 for the Enertech 21-5 up to 1,340,000 for the Enertech 44-50. The flows were observed by means of tufts and oil flow using a video camera-recorder and a 35mm automatic camera mounted in the rotating hub reference frame. Windspeed, power output, and other data were simultaneously recorded. In extending standard wind tunnel techniques for use on wind turbines the results show that, despite centrifugal effects superimposed on the aerodynamics, the combination of tufting and oil flow tests reveals the nature and many of the details of the flows involved. Patterns and types of separation are readily apparent. The typical low Reynolds number flow characteristics of these airfoils, including laminar separation bubbles, turbulent reattachment, and complete separation are observed. Full or partial reattachment due to tower shadow was observed on all three machines. Spanwise flow was seen most strikingly near the leading edge of the Enertech 21-5, Cyclic radial flow due to the tower dam effect was also noted.