Far-field properties of aerated water jets in air

• Far-field properties of aerated water jets in air were experimentally studied.
• Air injection at nozzle helps water jets spread much wider and produce smaller drops.
• Drop size distribution was Gaussian in aerated jets but complex in pure water jets.
• Terminal drop velocity was 20% smaller in aerated jets than in pure water jets.
• Jet trajectories were modeled using projectile theory with air resistance.

This paper presents an experimental investigation on aerated water jets at a 45° angle into air. Different amount of air was injected into the water jets upstream of a circular nozzle. The focus was on the bulk trajectories of the aerated jets, as well as the intensity, size and velocity of the water drops in the far-field. It was found that, the injection of air into water jets will significantly accelerate water jet breakup in air, causing the water jet to spread much wider and more uniform. Meanwhile, water drop size became substantially smaller, but drop velocity only became slightly smaller. On the horizontal plane at the same elevation of the nozzle, intensity of falling water drops was noticed to have a Gaussian distribution in the transverse direction, while a left-skewed Gaussian distribution in the longitudinal direction. At the location of maximum intensity, drop size and velocity distributions also approximated Gaussian distributions, while the size distribution could be more complex in a pure water jet. Terminal water drop velocity was correlated with drop diameter, and its value was 20% smaller in an aerated jet than in a pure water jet for the drops with diameters of 2–10 mm. The energy dissipation of these jets was significant as these jets broke down to drops with relatively small terminal velocities.