On transition mechanisms in vertical natural convection flow

Abstract

An experimental investigation has been made of the processes occurring during the natural transition from laminar to turbulent flow of natural convection flow of water adjacent to a flat vertical surface where the surface heat flux is uniform. Measurements of both the velocity and temperature fields were made over wide ranges of the heat flux and at various downstream locations. Of principal interest were the definitions of the boundaries of the transition regime and their determination at several values of the surface heat flux. The interaction of the velocity and temperature fields during transition was measured. Our results show that transition events are not correlated in terms of the Grashof number G*. The form G*/xn, where n is of order ½ was found to give satisfactory correlations. Measurements of the frequency and growth rate of disturbances indicate the primacy of the velocity field during transition and show that the growth of turbulence in the temperature field lags behind that in the velocity field. The study of the turbulence growth, in terms of intermittency factors in both the velocity and temperature fields, resulted in unambiguous criteria for the boundaries of the transition regime. Our results suggest a kinetic energy flux parameter E and a single value closely correlates both our measurements of the onset of transition as well as those from all past studies known to us, for both different fluids and heating conditions.