Turbulence characteristics of natural-convection boundary layer in air along a vertical plate heated at high temperatures

Abstract

Turbulence characteristics of a natural-convection boundary layer in air along a vertical plate heated at high temperatures are experimentally investigated. Two-dimensional velocity vectors and instantaneous temperature in the boundary layer at a wall temperature up to 300 °C are measured using a particle image velocimetry and a cold wire. From the correlation between the local Nusselt number Nu x and the local Grashof number Gr x , it was found that heat transfer rates even for a wall temperature of 300 °C are well expressed by an empirical formula obtained for low wall temperature and the region of transition from laminar to turbulence does not change much with an increase in wall temperature. In addition, the profiles of turbulent quantities measured at a wall temperature of 300 °C resemble those observed at low wall temperatures, and thus the effects of high heat on the turbulent behavior in the boundary layer are quite small. The measured velocity vectors and the higher-order statistics, such as skewness and flatness factors of fluctuating velocities and temperature, also suggest that the structure of large-scale fluid motions in the outer layer of the natural-convection boundary layer, closely connected with turbulence generation, is maintained even under high wall temperature conditions.