Hi, I am working with a droplet generation system that is designed to produce monodisperse droplets. A periodic disturbance of appropriate frequency (kHz) is applied to a piezoelectric ceramic, transferred to an orifice disk (fitted within the ceramic by means of a Teflon O-ring), then sent to the liquid jet. The disturbance then breaks up the jet into droplets. My question is in trying to understand the instability theory in liquid jet breakup. There are a number of articles that have investigated this subject, among them Savart(1833), Plateau(1873), Rayleigh(1878), and Weber(1931). Equations about the disturbance growth rate have been developed by Rayleigh and Weber for inviscid and viscous flow, respectively. I do not fully understand the derivation of these equations, but to my understanding, the disturbance they consider is one without a forcing function. I have also looked at other articles that used the disturbance growth rate equations to investigate their experiment involving a monodisperse droplet generator, but they do not mention anything about incorporating a forcing function in the derivation of the equations. Can anyone give me some insight on this? Shouldn't a forcing function be used to describe the disturbance that is being sent from a function generator to the piezoelectric ceramic, causing the orifice disk to vibrate, and creating droplet breakup? To my understanding Weber sent one disturbance to the jet, whereas I am sending a series of identical disturbances by means of a function generator. Wouldn't this alter the breakup predicted by Weber and thus change the growth rate equation developed by Weber?