Traveling wave generation on a swept wing subjected to surface roughness and free-stream turbulence.

What is it about?

Reducing aircraft drag is crucial for saving fuel consumption and emissions as air transportation demand grows rapidly. Laminar Flow Control (LFC) is a key technology for reducing skin friction drag by controlling the transition from laminar to turbulent, thus maintaining laminar flow over the aircraft. While swept wings are commonly employed in transonic and supersonic aircraft to prevent drag increase by shock waves, the boundary layers on these wings are more unstable than those on straight wings, leading to transitions at the leading edge. Since the transition is sensitive to external disturbances, its process is complex, varies, and has yet to be fully understood. To reveal the details of the transition process, we conducted direct numerical simulations (DNS) of swept-wing flows to explore the impact of surface roughness and free-stream turbulence on the transition. Our study mainly focused on traveling waves, the details of which need to be better understood. Results suggest that the frequency of free-stream turbulence plays a vital role in generating traveling waves, with further linearized analysis suggesting a potential transition process due to these waves.

Featured Image

Photo by Ross Parmly on Unsplash

Photo by Ross Parmly on Unsplash

Why is it important?

Under flight conditions with small free-stream turbulence, transitions due to secondary instability of stationary waves excited by surface roughness are considered dominant, and a lot of investigations on this process have been conducted. On the other hand, the situation is different, especially for large aircraft, because turbulence generated at the wing-fuselage junction contaminates the leading edge. The computational setup in this study took this situation into account, and the results provided new insight into the conditions for the traveling wave generation, which may be the source of the transitions. Further investigation of the generation mechanisms of the traveling wave is expected to facilitate the practical implementation of LFC technology for swept wings.