Design and control of crossflow instability field

Full turbulent transition is induced on a yawed flat plate with a displacement body system in a wind tunnel. First, the transition process is measured in detail using hot-wire anemometry and the smoke visualization technique. Second, control of turbulent transition is tried by applying selective suction system considering the flow structure in the transition region. It is found that the most amplified disturbance at the last stage of the transition is the secondary instability f₂. Therefore, it is concluded that turbulent transition in crossflow dominant boundary layer transition is driven by this secondary instability. Considering such transition flow structure, an effective technique for control of the transition is developed. Namely, by forming narrow streamwise suction slits along each streamwise crossflow vortex, appearance of the secondary instability is successfully delayed. Such a suction system has an advantage over a uniform suction system in that amount of suction air volume is much less than that for uniform suction, and far less energy is needed for transition control.