On the Interaction of Freestream Turbulence and Attachment-Line Boundary Layer

One of the possible forcing mechanisms for inducing transition from laminar to turbulent flow is freestream turbulence. Among the different transition mechanisms, freestream turbulence influences the cross-flow instability which occurs on swept wings. In order to understand better the physical interaction between freestream turbulence and boundary layer, this work analyses how the turbulence is distorted approaching a leading edge and whether it is amplified approaching a swept leading edge. The paper contains a brief literature review of both the two-dimensional stagnation point and three-dimensional attachment-line flows. This reveals that freestream turbulence amplification has been investigated for two-dimensional leading edge flows, but there is a lack of research on the swept leading edge. In addition, the paper presents some experimental results on a circular cylinder at various sweep angles. The results show that the phenomenon observed at the two-dimensional stagnation point also occurs at a swept attachment-line, although some differences are identified.