FLOW VISUALIZATION STUDIES ON VORTEX INSTABILITY OF NATURAL CONVECTION FLOW OVER HORIZONTAL AND SLIGHTLY INCLINED CONSTANT-TEMPERATURE PLATES.

Flow visulization experiments were performed in a low-speed wind tunnel to study vortex instability of laminar natural convection flow along inclined isothermally heated plates having inclination angles from the horizontal of theta equals 0, 5, 10, 15 and 20 deg. The temperature difference between plate surface and ambient air ranged from DELTA T equals 15. 5 to 37. 5 degree C and the local Grashof number range was Gr//x equals 1. 02 multiplied by 10**6 to 2. 13 multiplied by 10**8. Three characteristic flow regimes were identified as follows: a two-dimensional laminar flow, a transition regime for developing longitudinal vortices, and a turbulent regime after the breakdown of the longitudinal vortices. Photographs are presented of side and top view of the flow and of cross-sectional views of the developing views of the developing secondary flow in the postcritical regime.