Turbulent jet manipulation using two unsteady azimuthally separated radial minijets

The active manipulation of a turbulent round jet is experimentally investigated based on the injection of two radial unsteady minijets, prior to the issue of the main jet. The parametric study is conducted for the mass flow ratio C_m of the minijets to the main jet, and the ratio f_e/f₀ of the minijet frequency to the preferred-mode frequency of the main jet. It is found that the decay rate of the jet centreline mean velocity could be greatly increased if the two minijets are separated azimuthally by an angle θ=60°, instead of by θ=180°. This increase is a consequence of the flapping motion of the jet column, and the formation process and generation mechanism of this flapping motion are unveiled by careful analysis of the experimental data.