Experiment on Spatio-Temporal Turbulent Structures of a Natural Convection Boundary Layer

The spatio-temporal structures of a turbulent natural convection boundary layer along a vertical flat plate in air have been examined using a thermocouple rake and a pair of hot-wire/cold-wire arrangements. The instantaneous temperature profile clearly indicates the evolution of a large-scale motion originating in the outer region of the boundary layer. However, the space-time correlation measurements did not suggest the existence of any quasi-coherent structures such as low-speed streaks and bursts. The convection (or advection) velocity and characteristic length scales of turbulence were also investigated. The convection velocity exceeds the local mean velocity in the near-wall and outermost regions. The microscale of the thermal field shows a strongly anisotropic structure, and the integral scale indicates a large-scale structure normal to the wall.