Normal impact force of Rayleigh jets

Abstract

The surface-normal impingement of a liquid jet emanating from a nozzle is of use in numerous technological applications (e.g., surface cleaning, waterjet cutting, and needle-free injection). Upon impact, the (Rayleigh) jet is characterized as either a steady-state (time-invariant) jet, a wavy jet, or a droplet train. The present study experimentally investigates the force imparted by these three distinctly different processes for identical nozzle flow conditions (i.e., velocity and jet diameter). Force models are developed based on Rayleigh jet theory, and they are shown to compare well with the measurements. The force induced by the wavy jet is sinusoidal, oscillating about the steady-state force, while the droplet train force is discrete with periods of zero induced force. Due to conservation of momentum, the peak force experienced by the droplet train is significantly higher than that of the steady stream. This identifies the droplet train as the dominant process to obtain higher peak forces than the continuous stream counterparts during impact with a surface. This can then be used as a means to increase the performance of applications such as waterjet cutting and surface cleaning.