角柱の挿入により非定常化した平行平板間流れと熱伝達 : 第3報, 熱伝達特性と伝熱機構

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Two-dimensional numerical computation has been made for unsteady velocity and thermal fields realized in the channel obstructed by an inserted square rod. The previous papers were devoted to the discussion of the obtained velocity fields. The present paper deals with the thermal field and wall heat transfer. The streamwise distribution of time-mean local Nusselt number reveals that heat transfer is augmented by the flow unsteadiness in the region downstream from the rod. Its peak at x/H=1.6 is caused by the peak of instantaneous Nusselt number, which first appears at x/H=0.8 and moves downstream accompanying the value of peak height. At this peak position, instantaneous wall shear stress takes the value lower than its time-mean value. Therefore, dissimilarity between the heat transfer and the momentum transfer exists there instantaneously. The peak position also corresponds to the position inside a wall vortex. Above this wall vortex, another isolated vortex, which is a disconnected tongue of the separated wall layer, can be identified. The latter vortex induces a clockwise circular fluid motion around itself. This fluid motion causes the reduction of wall friction, the formation of wall vortex and the washing action of the wall. The washing action entrains fresh fluid from the downstream side under the isolated vortex, maintains the instantaneous Nusselt number larger there, and contributes to generate the instantaneous dissimilarity.
一般社団法人日本機械学会の論文
1991-04-25

角柱の挿入により非定常化した平行平板間流れと熱伝達 : 第3報, 熱伝達特性と伝熱機構

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