Influences of upstream floor roughness and aerodynamic parameters on swept-wing junction flow

This study examines several finite length NACA 0012 airfoils to explore how the angle of attack (α), the sweep angle (Λ) and the Reynolds number (Re) affect the junction vortex and horseshoe vortex. Upstream floor roughness and turbulence intensity (T.I.) influence the wing-junction flow was also studied. The junction-flow structures at low Reynolds numbers were visualized using the smoke-wire technique. The smoke-streak flow patterns were classified into two characteristic modes — horseshoe vortex and non-horseshoe vortex. The horseshoe-vortex patterns were further categorized as the junction-vortex mode and non-junction-vortex mode. The velocity vectors were measured using the particle-image velocimetry (PIV), and the data was utilized to calculate the junction vorticity (Ω). Experimental results indicate that the straight wing has the maximum junction vorticity. The Ω decreases with increasing α and Λ and with decreasing Re. The Ω decreases with increasing T.I. The upstream T.I. generated by the mesh fences was more significant than that produced by sandpapers.

► This study shows the generation mechanism of the horseshoe vortex at low Reynolds numbers.
► The flow patterns are classified as horseshoe-vortex mode and non-horseshoe-vortex mode.
► The effect of α on Ω shows that Ω decreases with the increase of α and the maximum Ω occurs at Λ = 0°.
► The effect of Λ on Ω displays that Ω decreases with the increase of Λ.