Flow Loss and Flow Structure of Circular Arc Blades with Different Leading and Trailing Edges

3.2 Application of Analytical, Computational and Experimental Methods

Compared with circular arc blade with rounded leading and trailing edges, the circular arc blade with flat leading and trailing edges can be produced relatively cheaper by NC-milling machine. However, the flat leading and trailing edge of the blade may also cause relatively higher flow loss. At present, there is few available information in the open literature focusing on the flow loss and behavior of circular arc blade. In particular, the influence of leading and trailing edge geometry on the flow structure remains unknown. Therefore, two questions are raised: Firstly, how large is the flow loss and flow turning angle of circular arc blade. Secondly, how much is the influence of the leading and trailing edge geometry on flow loss and flow structure.
In this paper two kinds of circular arc blade with constant thickness are examined by numerical and experimental methods. The first circular arc blade has rounded leading and trailing edge, the leading and trailing edge of the second blade are flat. Both blades have a chord length of 100 mm and a camber angel φ of φ = 20 degrees. The stagger angle λ = 30 degrees. The investigated spacing ratio t/l is 1.0. In order to investigate the influence of Reynolds number on the flow loss and flow structure, the Reynolds Number was Re = 200000 and Re = 400000. All examinations were performed for different incidence angles from i = -15 degrees to i = 10 degrees with a stepwise movement of 5 degrees.
The paper shows flow loss in dependence of incidence and Reynolds number. The influence of the sidewall on the flow loss and flow structure is also taken into account. The difference between two- and three- dimensional flow loss of both investigated blades is concluded. The flow loss and flow structure of both blades are investigated and compared. The flow structure is shown on the basis of numerical and experimental oil-flow picture. Especially, the flow behavior such as separation bubble at the leading edge, secondary flow and the flow structure in the corner between the blade and the corresponding sidewall is shown and discussed.