Abstract

Nonlinear development of streak instability modes is examined up to the turbulent stage experimentally through artificially producing spanwise-periodic low-speed streaks in a laminar boundary layer. The experiment is focused on the subhar- monic sinuous mode of instability. The sinusoidal motion of low-speed streaks caused by the streak instability is maintained three or four wavelengths down- stream beyond the nonlinear saturation stage of instability, and subsequently breaks down. After the breakdown, near-wall low-speed streaks with lateral spacing of 100 wall units newly develop, and the mean velocity profile starts to exhibit the log-law. It is also found that the interaction between the quasi- streamwise vortices developing along the neighboring streaks causes large-scale arch-like vortices to develop in the region away from the wall.

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