安定成層内プルームのスペクトルおよび乱流遷移の促進と乱れの抑制 : 逆遷移と再層流化〔熱工学, 内燃機関, 動力など〕

概要

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Spectrum of the plume in a stably stratified ambient was elucidated to have gradients -9/2 and -8.0 at laminar state, and -5/3 and -3.0 at turbulent state, in addition the frequency band of the turbulence was higher than that of the swaying motion. By employing the above results, flow regimes, i.e. laminar, transitional, and turbulent, at any location can be determined. By plotting flow regimes on visualization photos, retransitional and relaminar phenomena are specified. Stable stratification generates turbulence, suppresses turbulence, and leads to reverse transition and relaminarization, which do not occur in the plume in an unstratified ambient, thus characterizing the plume in a stratified ambient. The Grashof number for the beginning of transition is approximated as Gr_s=9.15×10^5{Q[W/m]}^1.62. Critical heat rate Q for the beginning of either the transitional or turbulent regime is Qs[W/m]=1.30-2.75 or Qe[W/m]=5.10-8.73.
一般社団法人日本機械学会の論文
1997-10-25