Modern thermal design practices often rely on a predictive simulation capability--although predictability is rarely quantified and often difficult to confidently achieve in practice. The computational predictability of natural convection in enclosures is a significant issue for many industrial thermal design problems. One example of this is the design for mitigation of optical distortion due to buoyancy-driven flow in large-scale laser systems. In many instances the sensitivity of buoyancy-driven enclosure flows can be linked to the presence of multiple bifurcation points that yield laminar thermal convective processes that transition from steady to various modes of unsteady flow. This behavior is brought to light by a problem as simple as a differentially-heated tall rectangular cavity (8:1 height/width aspect ratio) filled with a Boussinesq fluid with Pr= 0.71--which defines, at least partially, the focus of this special session. For the authers purposes, the differentially-heated cavity provides a virtual fluid dynamics laboratory. In conclusion, they emphasize that the differentially-heated cavity, in addition to its relevance as a model of convective heat transfer, turns out to be a real fluid mechanics laboratory in itself. The spatial structure of the flow is made of vertical and horizontal boundary layers, of corner structures, of a stratified core, which depend very sensitively on the aspect ratio, Prandtl number and thermal boundary conditions (even a fly-wheel structure can be found at low Pr). All these features cooperate to give rise to very complex time behaviors resulting from several instability mechanisms, traveling waves in the vertical boundary layers, thermal instabilities along the horizontal walls in particular, which can interact strongly with internal wave dynamics.
PDF
download
878987797
028-85220240
