TURBULENT STRUCTURES AND MODELLING OF SPATIALLY DEVELOPING THERMALLY-STRATIFIED TURBULENT BOUNDARY LAYERS

摘要

In order to investigate quasi-coherent structures, motions and heat transfer in various thermally-stratified boundary layers, direct numerical simulations (DNS) of the boundary layers of these flows have been carried out. The turbulent structures (vortex, streak, heat transfer, etc) are qualitatively shown by conventional visualization techniques. Also, to quantitatively indicate the structure, a unique detection algorithm for well-ordered motions is used, i.e., the trajectory analysis method based on the (u, v)-quadrant analysis is employed to observe the relationship between well-ordered flow motions and heat transfer. Consequently, the quasi-coherent structures, motions and heat transfer in various thermally-stratified boundary layers are clearly discovered. On the other hand, in order to adequately predict turbulent boundary layers with various thermal stratifications, an appropriate turbulence model should be employed in the calculation. Thus, using a database obtained by DNS, the strict assessment of turbulent heat transfer model is made so as to construct a reliable advanced turbulence model. The results of in-depth turbulent model evaluation are indicated, in which we have explored the prediction potential of the proposed non-linear eddy diffusivity models for momentum and heat in both stable and unstable stratified boundary layers.