Experimental study of the K-regime of breakdown in straight and swept wingboundary layers

In this Brief Communication, the nonlinear evolution of periodical disturba nces generated by an external sound field in a swept wing boundary layer is presented. All experimental results are compared with corresponding data f or a straight wing configuration. The Tollmien-Schlichting instability has been studied, and it was found that the disturbance flow field remained hig hly deterministic and periodic in both time and space until the latest stag es of the transition. A frequency-wave number Fourier analysis shows that t he disturbance spectra comprise only the fundamental wave and its higher ha rmonics. The K-type breakdown scenario was observed, and the nonsymmetry of flow patterns in the swept wing boundary layer was found to be due to the presence of the cross flow. (C) 2001 American Institute of Physics.