Visualization of flow over a thick airfoil with circular cross-sectional riblets at low Reynolds numbers

This study qualitatively investigated the effects of riblets with circular cross section on the aerodynamic performance of a thick airfoil. Smoke lines inside a wind tunnel visualized the flow fields around the airfoils with and without riblets to compare the location of the separation point, the stability of the visualized smoke lines near the wake and the size of the wake region for 0 degrees-20 degrees angles of attack, at a Reynolds number of 2 x 10(4). Four sizes of riblets with the height-to-chord ratios of 0.002, 0.005, 0.008 and 0.01 were attached to the thick airfoil to prepare the textured models for the visualization tests. The sizes of the wake region were measured at four cross sections behind the models by image processing. Due to the fluctuations of the wake size, many consecutive images were considered for averaging the wake size at each section. The results showed the wake size to be changed as a result of using riblets depending on the size of riblets. The textured model with the height-to-chord ratio of 0.005, compared to the smooth model, significantly decreased the wake size for all the angles of attack.