UNSTEADY LIQUID JETS

The behaviour of unsteady liquid jets in a gas atmosphere is mainly go verned by the conservation of momentum and the interaction with the en vironment. In this article it will be shown that many of the particula r effects in the propagation and desintegration of unsteady jets are s imply explained by the conservation of initial momentum. Many of the d istortions and peculiar shapes of the liquid elements of the jet can b e explained by a time and space development of weak initial distortion s of momentum in travelling waves during propagation. The first part o f the paper is devoted to the droplet formation in liquid jets of mode rate Weber numbers in the order of ten. In this regime and higher the surface tension is not the governing influence of instability of jet d ecomposition and hence of the droplet formation. If there is a high fr equency distortion of the velocity which is artificially implemented i n our experiments by a special device, but under usual conditions also existing by turbulence or source distortions of the nozzle flow the c oncentration of mass in packets in a kind of shock formation is the ma in reason for droplet formation. The frequency of droplets in space an d time is given by the frequency of the distortion. The amplitude and phase is also given by the initial values of the driver for these quan tities. For large amplitudes and low frequencies the jets are decompos ed in very peculiar shapes, which can be very simply explained by the collision of packets of concentrated mass on the axis of the jet motio n. The whole range of phenomena can be understood in a theoretically e legant manner by a Lagrangian transform of the nonlinear equations of motion together with some plausible considerations about the lateral m otion. Solutions for the droplet formation and the formation of liquid films in different shapes can be achieved this way. As an illustratio n of the whole range of beautiful and regularly reproducible details o f jet decomposition some photographs will be shown which summarize the phenomena and give an idea of the importance of systematic investigat ion of the sometimes very confusing appearance of fluid jets.