EFFECTS OF FREE-STREAM VELOCITY ON TURBULENT NATURAL-CONVECTION FLOW ALONG A VERTICAL PLATE

A detailed measurement of heat transfer and fluid flow of turbulent boundary-layer air flow in natural and mixed convection adjacent to an isothermal vertical flat plate are reported. A cold-wire anemometer and laser Doppler velocimeter were used, respectively, to measure simultaneously the time-mean turbulent temperature and velocity distributions and their turbulent fluctuations. In this experimental study, measurements of the flow and thermal fields were carried out at one streamwise location, x = 2.7 m, for a temperature difference AT of 30°C between the heated wall and the free-stream air (with a corresponding local Grashof number Grx = 6.45 x 10^10), and for a range of dimensionless free-stream velocities 0 < U(unlimited) > 0.289. The effect of small free-stream velocity on the turbulent natural convection is examined. These results reveal that when a small free-stream velocity is introduced on turbulent natural-convection flow, transition is delayed, turbulence is suppressed, and the flow may relaminarize, causing the heat transfer rate from the heated wall to decrease.