Study of Active Jet Control by Acoustically Driven Secondary Film Flow Influence of Velocity Ratio and Acoustic Strouhal Number

Active control of the diffusion of a circular jet was attempted by application of a secondary film flow around the jet. Sinusoidal acoustic excitation of the film flow was carried out for VR values of 0.5 and 1.0, where VR is the ratio of the film flow velocity to the main jet velocity. For VR = 0.5, the diffusion of the jet was suppressed compared to that of a single jet but it was somewhat enhanced by the acoustic excitation. The acoustic excitation shortened the potential core of the jet; however, the entrainment of the ambient flow was far less than in the case of a single jet, regardless of degree of excitation. For VR = 1.0, diffusion was enhanced by acoustic excitation. Both turbulence intensity and ambient flow entrainment increased downstream of the jet. We conclude that film flow can control diffusion and that acoustic excitation can enhance the diffusion of jet flows. It is worth investigating this mechanism in detail in future studies.