Wave interactions in swept-wing flows

The leading-edge region of swept wings is dominated by the crossflow instability, resulting in vortices that all rotate in the same sense. The effect of these vortices on the behavior of other disturbances is examined and an interaction between these and disturbances of half the dominating crossflow wavelength is predicted. According to theory, the interaction is of crossflow-crossflow type. The effect explains the anomalies found in the experimental observations of Saric and Yeates (1985). Visually Saric and Yeates observe vortices at the wavelength predicted by linear theory; however, in their hot-wire measurements they find that the second harmonic dominates disturbance growth, with eventually three times the amplitude of the primary wave. In this case, the usual transition-prediction methods would fail, clearly indicating the importance of studying interactions of this sort.