中間レイノルズ数域におけるフィン列の流動・伝熱特性 : フィン後流長さの影響  [in Japanese] Flow and Heat Transfer Characteristics of Fin Arrays in the Middle Reynolds Number Range : Effect of the Fin Wake Length  [in Japanese]

Unsteady flow and heat transfer characteristics were studied numerically for an in-line array of triplet fins located in a channel in the middle Reynolds number range. Flow unsteadiness is confirmed to be noticeably affected by geometric parameters, i.e., fin thickness and fin wake length to fin length ratio. Even in the case where the fin thickness is so small that the wake of a single-fin remains steady, flow can become unsteady in the three-row fin array and the flow pattern is noticeably changed by changing the value of L_w/L, the wake length to fin length ratio. The heat transfer performance of the in-line fin array in also noticeably affected both by the fin thickness and the fin wake length to fin length ratio. This is produced by the flow unsteadiness. It is found that most effective heat transfer augmentation is attained with L_w/L=0.5. This optimum value of L_w/L does not change even if fin thickness is varied. Discussion was also made to the mechanism of heat transfer enhancement caused by the flow instability. It is concluded that the mechanism of heat transfer enhancement does not change with L_w/L value and is the same as that found in the previous study ; i. e., accelerated wake recovery by the mixing caused by the generated vortices in the wake and the washing action exerted by the vortices flowing along the fin surface. The latter produces the dissimilarity between the heat transfer and momentum transfer.