Skin-friction topology of wing–body junction flows

High-resolution time-averaged skin-friction fields in wing–body junction flows are extracted from luminescent oil-film visualization images taken at different viewing angles and positions in a wind tunnel. The complete skin-friction topology on the wing–body junction surface is reconstructed, and isolated singular points and separation and attachment lines are identified. The evolution of the topological structures is discussed as the angle of attack of the wing changes. The topological consistency of the extracted skin-friction fields is examined by applying the Poincare–Bendixson index formula. The relationship between the skin-friction topological features and flow structures like the horseshoe vortex, secondary separation, separation bubble and wingtip vortex is explored.