Effect of local surface roughness on flows over airfoils at aerodynamically low Reynolds numbers

The influence of a finite boundary layer trip on the flow over a NACA 0018 airfoil is investigated experimentally. Oil flow visualization along with particle image velocimetry (PIV) and direct force measurements, are conducted at aerodynamically low chord Reynolds numbers (~100,000) that produce a laminar separation bubble on a smooth model. Oil flow visualization is utilized to identify the spanwise extent of the effect of the roughness element and the changes in the baseline laminar separation bubble location and size. PIV measurements are carried in multiple planes to provide quantitative insight into the changes in the laminar separation bubble topology and dynamics due to the presence of the finite trip. A comparative analysis of the flow and direct force measurements is conducted to identify the associated effect on airfoil performance.