Abstract
An active control on a diffusion of a circular jet is tried by applying the secondary film flow around the jet. VR, the ratio of the film flow velocity to the main jet velocity is chosen to be 0.5 and 1.0, and the sinusoidal acoustic excitation on the film flow is attempted. For VR=0.5, the diffusion of the jet is suppressed compared to the single jet but it is somewhat recovered by the acoustic excitation. The effect of the acoustic excitation manifests on the shortening of the potential core of the jet. However, the entrainment of the ambient flow is far smaller than the single jet regardless of excitation. For VR=1.0, the diffusion is promoted with the acoustic excitation. Turbulence intensity and the entrainment of the ambient flow increase in the downstream region of the jet. It is concluded that the film flow can control the diffusion and acoustic excitation is effective for promoting the diffusion of jet flows. It will be worth to investigate its mechanism in detail in future studies.
