Opposition control of turbulent spots

Opposition control of artificially initiated turbulent spots in a laminar boundary layer was carried out in a low-turbulence wind tunnel with the aim to delay transition to turbulence by modifying the turbulent structure within the turbulent spots. The timing and duration of control, which was carried out using wall-normal jets from a spanwise slot, were pre-determined based on the baseline measurements of the transitional boundary layer. The results indicated that the high-speed region of the turbulent spots was cancelled by opposition control, which was replaced by a carpet of low-speed fluid. The application of the variable-interval time-averaging technique on the velocity fluctuation signals demonstrated a reduction in both the burst duration and intensity within the turbulent spots, but the burst frequency was increased.

Automated summary

This study conducted opposition control of artificially initiated turbulent spots in a low-turbulence wind tunnel in order to delay the transition to turbulence by modifying the turbulent structure within the spots. Through wall-normal jets, the high-speed region of the turbulent spots was cancelled and replaced by a carpet of low-speed fluid. The variable-interval time-averaging technique showed a decrease in burst duration and intensity within the spots, but an increase in burst frequency.