Turbulent Transition Mechanisms of Natural Convection over Upward-Facing Horizontal Plates

Turbulent transition mechanisms and heat transfer characteristics of the natural convection over heated, horizontal plate were investigated both experimentally and analytically. An unsteady, 3-D numerical analysis has been performed on the water flow over 150 mm-wide plate heated with constant heat flux. The analytical results showed that longitudinal vortices play a crucial role on the turbulent transition over the plate. The vortices appear first in the laminar boundary layer at certain distance from the leading edge. Then, they detach from the plate and become distorted toward downstream. Meanwhile, the flow and temperature fields over the plate were visualized experimentally. The results confirmed that the above transition actually occurs over the plate. Moreover, the local heat transfer coefficients predicted by the analysis coincide well with those measured by the experiments.