Blasius boundary layer evolution is studies by means of bicoherence calculations. The layer is acoustically excited at the T-S frequency to provide a controlled transition. Measurements are made using a smooth surface as well as various roughness patterns. The bicoherence calculations are used to determine the extent to which frequency resonant velocity fluctuation waves can participate in energy exchange. The emphasis is on downstream variation of the individual interactions among harmonic modes. A limited picture of the role of quadratic wave interactions is revealed
