Development of Advanced Diffuser by Controlling Flow Actively

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A final goal of this study is to develop a design of an advanced diffuser with high efficiency. Effects of an incoming turbulent disturbance on performance in a two-dimensional diffuser are studies experimentally. Main results of this study are summarized as follows.(1) An incoming turbulent wake of a moving rod in a plane perpendicular to a main flow improves a pressure recovery coefficient of the two-dimensional diffuser with and without separation. This is a new finding in this field.(2) Effects of a quasi-steady incoming wake of the rod on performance in the diffuser are investigated. The rod is installed upstream of the inlet of the diffuser. Time-mean velocity distributions and turbulent intensity distributions are presented for several combinations of the diameter and position of the rod. It is found that there exists an optimum combination for the improvement and reduction of loss. An interaction between the wake and the separated shear layr are visualized in a water channel. There is no separation when the pressure recovery coefficient attains the maximum.(3) A new concept of a design of the diffuser under the unsteady flow condition is discused. The separated shear-layr is controlled actively by using a sinusoidal disturbance. An application of the control to the diffuser with separation is discussed in this study.