Passive mixing control of plane parallel jets

An experimental study on the mixing of two plane, unventilated, parallel jets reveals an instability characterized by sinuous ‘‘flapping’’ of the jets and enhanced mixing of the jets with the ambient fluid. The frequency and amplitude of the instability is shown to be a function of the jets’ spacing and momentum flux ratios, with the maximum mixing occurring for cases with matched momentum flux. When the momentum flux of the two jets is mismatched by as much as a factor of three, the flow becomes steady. Schlieren flow visualization and hot-wire anemometry demonstrate and quantify the large-scale mixing. The instability has a strong frequency and amplitude dependence on the momentum ratio of the jets. The Strouhal number is also found to decrease with the spacing between the jets. The instability described provides a means to passively control the jet mixing with the ambient.