Controllable multiple mixing monodisperse droplet streams generation using wavelength-modulated disturbances

In this paper, we study the breakup of a circular jet disturbed by wavelength modulation to produce periodic but non-uniform patterns of droplet sizes. Instead of a single wavelength disturbance, a series of perturbations containing two different wavelengths in one cycle was applied to excite the jet. Jet breakup patterns and droplets formation under composite disturbances were derived based on the classic linear theory of instability. Experiments indicate that the jet breakup length and the resultant droplet size can be precisely controlled. The length of the coexistence stage of two sizes of droplets depends on the difference in the growth rates of each disturbance. By applying three and four wavelengths in the perturbation, we also demonstrate the potential of this concept to generate more mixing droplet streams. This active droplet generation method with well processed control of non-uniform droplets would be advantageous in various potential applications.