Numerical and experimental study on buoyancy induced flow transition in upward mixed convective flow through vertical flat ducts

摘要

Buoyancy induced flow transition in low-speed upward flows through vertical flat duct were studied for two representative cases: the case flow was heated uniformly from both side walls and the case flow was heated from only one side wall. Flow pattern were visualized by the dye injection method. In either case, fluctuation of streak-line and ensuing transition to three-dimensional non-laminar flow were observed halfway through the duct. Nusselt number increased rapidly with flow transition and did not change so much with downstream distance in the non-laminar flow regime. However, the two cases differed much in the condition for transition and the transition process. A numerical code for three-dimensional unsteady convection was developed, and the mixed convective flows were investigated numerically. Comparison between numerical results and experimental results was remarkably good. Based on these results, the reasons why the two cases differed much in transition process were discussed.