Turbulent Free-Convection Boundary Layer on a Vertical Heated Plate: Regularities of the Temperature Layer

Analysis is made of the results of experimental investigations of temperature and velocity profiles in a turbulent free-convection boundary layer on a vertical heated plate. An inference is made of the absence of adequately clear concepts of the velocity and temperature laws of the wall, as well as of the urgency of determining the main (universal) temperature, velocity, and linear scales which provide for the similarity of velocity and temperature profiles in the boundary layer cross sections. Main attention is given to the investigation of regularities of the temperature layer. In contrast to the existing one-parameter concepts of the temperature law of the wall, which are based on the assumption that the temperature profiles are independent of the dynamic characteristics, a two-parameter temperature law of the wall is suggested which takes into account the effect of the Grashof number, i.e., of the dynamic characteristics on the thermal ones. Based on the results of analysis of available experimental data, the suggested temperature law of the wall is realized in the form of a two-parameter family of logarithmic temperature profiles and a model of effective thermal diffusivity. A complete description is given of the structure of the inner region, namely, of the thermal sublayer and of the transition (buffer) and logarithmic regions. A full-scale algebraic model of turbulent thermal diffusivity for the entire layer as a whole is suggested. The similarities and differences of characteristics are observed between the flow being treated and a forced-convection turbulent boundary layer on a flat plate.