A Short Note about the Impact Action of a Water Jet Stabilized by a Coaxial Air Stream in the Air and Underwater.

Josef Poláček,Martin Tyč,Irena Marie Hlaváčová

doi:10.3390/ma14175015

Abstract

A new original method, applying a coaxial protective airflow, was tested aiming to improve the pure water jet efficiency in surface layer removal or medium hard materials cutting or blasting. The dual action of the air flow is expected: the air co-flowing the water jet with approximately the same velocity should prevent the central jet from breaking up into tiny droplets in the near field, and simultaneously, it should support jet decomposition into big parts with enough destructive potential in the far-field. A brief survey of the relevant literature dealing with the water jet instability is presented, introducing four recognized breakup regimes. An original cutting head designed to generate a waterjet surrounded by protective coaxial air flow is introduced. The submitted device is supposed to operate within the first wind-induced regime. Two types of experiments, consisting of blasting limestone bricks placed either in the air or underwater, were realized. The depths of kerfs produced with different water pressures and air overpressures were evaluated. While no substantial positive effect was recognized in the air performance, the submerged blasting of the same material under similar conditions appeared to be promising.

Highlights

The disintegration effect of a pure water jet impacting on the material is given by the impact pressure of the fluid droplets falling on the surface of the material
The aim of our work is to streamline the action of the water jet on the surface of the processed material by eliminating unwanted secondary decay of the water jet, which is caused by shear forces at the interface of the water jet and ambient air
We investigated the disintegration effect on the surface of a material caused by a pure water jet and a water jet cooperating with a coaxial air stream

Summary

Introduction

The disintegration effect of a pure water jet impacting on the material is given by the impact pressure of the fluid droplets falling on the surface of the material. This pressure is proportional to the impact velocity of the droplets and the properties of the liquid (namely its density and speed of sound propagation). Proved to be more reliable and have entered the industrial phase Another way of pulsing jet generation, applying self-excited oscillations in the nozzle, has attracted waterjet researchers for years [4,5,6,7] but it still remains in the experimental phase it should be more energy-saving and environmentally friendly. Substantially, the liquids with different properties (density, viscosity, surface tension) are used and so there is plenty of literature dealing with the problem

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