Tham khảo tài liệu 'fundamental and advanced topics in wind power part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Inboard Stall Delay Due to Rotation 49 Application A hypothetic blade with constant incidence and chord along the span is chosen to analyze the rotational effects on the boundary layer of a wind turbine blade. In this example an external flow with the distribution of velocity on the surface of blade given by Eqs. 5 and 6 is imposed. Fig. 7. Relationship between the separation points and the blade radius a at stall incidence b at prestall incidence. Fig. 8. Influence of the r c ratio on the suction pressure coefficient and lift coefficient at prestall incidence Cpm I 6 a 14 deg . The curves plotted in Fig. 7 are calculated on the prestall Cpm 6 and stall Cpm 10 conditions with a Reynolds number of 106. Relationships between the separation points and the blade radius are shown in Fig. 7 in which two apparent trends can be seen. Firstly as compared to the 2-D prestall condition r c the separation point is postponed because of the effect of Coriolis force which acts as a favorable pressure gradient tending to delay the separation to a point further downstream towards the trailing edge. It is shown that as the radial location r c decreases the separation point moves towards the trailing edge and consequently the suction side distribution of the pressure coefficient moves towards lower levels Chaviaropoulos Hansen 2000 Fig. 8. The drop of the pressure coefficient along 50 Fundamental and Advanced Topics in Wind Power the suction side can be related to the separated area on the blades which reduces in comparison with the 2-D r c . Secondly in the stall incidence condition leading edge separation bubbles are formed on the upper surface of the blade at the root area which delays the occurrence of massive separation. Beginning at the root of the blade the bubble continues to stretch towards the trailing edge and at approximately r c 4 where the bubble stretches all the way to the trailing edge the flow separates over the whole airfoil Dumitrescu Cardoậ 2010 In the next .
