周期変動噴流を用ぃた後方ステップ流れの能動的制御（第1報，噴流条件の影響とはく離流れ場の構造）

摘要

流れのはく離・再付着現象は，航空機の空力特性やrnディフューザ等の流体機械要素の性能，燃焼器・熱交rn換器のような熱流体機器の作動効率に大きな影響を与rnえる．そのため，従来からはく離・再付着を伴う流れrnの制御に関する研究が数多くなされているが，最近はrn流れの状況に応じて制御パラメータを幅広く変化させrnることができる能動的流れ制御に注目が集まってきてrnいる．%Backward-facing step flows with horizontal or vertical synthetic jets fed from the vicinity of the step edge have been investigated to clarify effects of the synthetic jets on separated-reattachment flows as well as to obtain new knowledge for the active control of the flows. Relations between reattachment length and flow control parameters, such as frequencies and velocities of the jet, have been studied. Then details of the flow fields have been obtained with time-mean as well as phase locked average procedures. Changes in the reattachment length for constant non-dimensional jet velocity are mostly determined from a ratio of the jet frequency to natural frequency of velocity fluctuation without a jet. The reattachment length becomes a minimum when the jet frequency ratio is around unity and decreases in proportion to the non-dimensional jet velocity to the power of -0.11rn～-0.13. The feed of the synthetic jet makes shear layers in the downstream of the step edge bernperiodical organized vortices which induce organized periodic velocity fluctuation and causes non organized random fluctuations with lower frequencies. These velocity fluctuations stimulate mixing of the fluids in the main stream and in the reverse flow region to promote the flow reattachment.