Transition to unsteady natural convection flow in a prismatic enclosure of triangular section

Natural convection in a prismatic enclosure of triangular section with the top cooling and the bottom heating is investigated using three dimensional (3D) numerical simulations for a wide range of Rayleigh numbers from 100 to 1.25 × 106. The numerical result has been compared with the experiment. The development of natural convection flows in the cavity following sudden heating and cooling involves three stages: an initial stage, a transitional stage and a fully developed stage. Transition to unsteady natural convection flow in the fully developed stage, dependent on the Rayleigh number, is described. The flow structure including transversal and longitudinal rolls is characterized and the corresponding mechanism is discussed. The critical Rayleigh number for the transition to unsteady natural convection flow is obtained. The dependence of heat transfer on the Rayleigh number is quantified.