凹面に沿う非圧縮性境界層の遷移

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書誌事項

タイトル別名
  • オウメン ニ ソウ ヒアッシュクセイ キョウカイソウ ノ センイ
  • Transition in an Incompressible Boundary Layer along a Concave Wall

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抄録

凹面に沿う非圧縮性境界層の遷移を実験的に研究した.凹面に沿う境界層の特徴である縦渦の発生と発達についての研究,および,縦渦の発達によって作られた境界層内の三次元的な場に重畳された進行波の振舞の研究を行ない,その結果,縦渦による三次元性の影響が凹面に沿う境界層の遷移に対して支配的であることがわかった.

Results of experimental investigation on instability leading to transition in the subsonic boundary-layer flow along a concave wall are presented. Hot-wire measurements, pitot-tube measurements, and dye observations reveal a spanwise variation in velocity profile having a definite wave number whether the boundary layer is laminar or turbulent. The variation is interpreted as produced by a system of vortices with axis in the streamwise direction. For the laminar boundary layer the vortices are just those expected from the theory of laminar instability. The wave amplitude distribution is in good agreement with theoretical prediction, but the wave amplification rate agrees with theoretical value only when the amplitude is small. For the turbulent boundary layer the experimental results are accounted for by the theory of laminar instability in which the molecular viscosity is replaced by the eddy viscosity. In both cases, however, the theory tells nothing about the mechanism by which the wave length is determined. Transition Reynolds number is reduced in the boundary layer along a concave wall compared with that on a flat plate. In order to gain a deeper insight into this problem, the behavior of the propagating wave produced by a vibrating ribbon is investigated by hot-wire measurements. It is found that the spanwise variation in mean flow has a decisive effect on the development of the wave in the boundary layer. The wave is most strongly amplified in the section where the velocity profile is deformed into an unstable form. It appears therefore that the system of streamwise vortices indirectly affects the transition in the boundary layer along a concave wall by making the flow field three dimensional.

資料番号: SA4135036000

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