Observation of the transition of the boundary layer flows on a flat plate due to the thermal instability

Abstract

The developing process of the boundary layer flows from laminar to turbulent is observed when a laminar boundary layer flows on a horizontal flat plate is heated locally from below.
The thermal instability occurs in the boundary layer flow over the heated section and the longitudinal vortices appear in the spanwise direction. As the longitudinal vortices move in the downstream direction, they become unstable and merge into large scale vortices. Simultaneously, a streamwise periodic structure also appears in the flow.