Detailed measurements were made on the laminar-turbulent transition of a two-dimensional wake with three kinds of imposed disturbances, the natural disturbance in a wind tunnel, a sound of single frequency, and a sound of two frequencies from outside. In all cases the transition to turbulence is gradual. The production of the fluctuation energy from the mean motion can be negative in a certain stage of the transition.nWhen a sound of single frequency is introduced into the wake, the induced velocity fluctuation is regular and periodic and it persists, resulting in a transition delay. When a sound of two frequencies (f1 and f2) is introduced, two velocity fluctuations are induced. They grow independently while amplitudes are small. When amplitudes exceed certain values, two fluctuatoins interact and both amplitudes are reduced. An¬other result is the generation of velocity fluctuations of frequencies of f1—f2,2(f1—f2), . . ., and f1+f2, 2(f1i+f2), .... The behavior of a slow, irregular fluctuation found in the natural transition resembles that of f1—f2 component in many respects. Both fluctu¬ations must be generated by the same process. The amplification of randomness in the transition process may be accomplished by the mutual suppression of amplitudes and by the generation of low-frequency components from high-frequency components.
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