同軸二重円管噴流の強制加振

概要

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Circular coaxial jets have been experimentally studied, and the outer annular jet is excited by the sound wave from speakers. We have measured velocity, turbulent intensity distributions and the power spectra of the fluctuating velocity of the coaxial jets for different configurations of the outer nozzle with a pipe length of L/D_0=0 to 5 and for various values of the velocity ratios of inner jet to outer jet, in order to examine the effects of excitation. For the nozzles with the pipe length of L/D_0≧2 and the forcing frequency of f_0>200Hz, the recirculating region shrinks and moves upstream. The intensity of fluctuating velocity in the outer mixing region for the jets of L/D_0=0 and 0.5 increases at f_0=300〜400 Hz. It is confirmed that the increase of turbulence intensity is related to that of the fundamental frequency component. For the jet of L/D_0=1, turbulence suppression is observed at the forcing frequency of about 600 Hz. It is found that the suppression effect is a consequence of earlier transition of the shear layer vortices. For the nozzle with L/D_0=2, the vortex pairing event has been recorded through phase-locked measurements at the forcing frequencies of about 300〜400 Hz. The velocity fluctuation intensity is confirmed to be enhanced by vortex pairing.
社団法人日本機械学会の論文
1995-03-25