人工音響ループによる二次元噴流不安定波周波数の制御

概要

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It is prevailingly known that acoustic sound frequency emanated from the trailing edge of two-dimensional airfoil varies with the so-called ladder-like structure and discontinuously jumps to other ladder-like states with increase of the freestream velocity. In order to unravel such critical conditions resulting in the ladder-like structure, two-dimensional jet with no aerodynamic sound emission impinging to still air is used, because acoustic sound is accepted to the flow at the jet exit. That is, when unstable disturbances growing in shear layer of the jet are excited by a loud speaker, the acoustic feedback loop automatically selects one frequency from broad-band frequencies of the shear layer. Ladder-like structures are found to be similar to airfoil trailing-edge noise. It is also found that each rung slope and jump frequency between ladder-like states show good agreement with existing empirical model. Furthermore, when the remnant of the distance between speaker and jet divided by wavelength of a selected acoustic sound is equivalent to half wavelength of sound, selected frequency jumps to other state. Also, hysteresis phenomenon is observed in cases that the speaker approaches to the jet flow or goes away.
THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCESの論文