Visualisation and quantitative analysis of the near nozzle formation and structure of a high pressure water jet in air and water.

Abstract

High pressure water jets (HPWJ) with Reynolds numbers in the scale of 10 4 are visualised by high speed photography in air and water. Moreover, suitable measurement techniques are tested and verified by quantitative analysis of the emerging jet to identify the influence of the surrounding fluid on the HPWJ.The HPWJ process known from industrial applications can be adapted to the field of rock drilling. In this specific case, the HPWJ is used to cut and destroy rock in deep geothermal reservoirs. The process is known as jet drilling. Although there have been research activities in this field, the process itself is not well understood so far and practical applications are rare. Therefore, the aim of our work is the visualisation of the process to increase the knowledge of waterjet and rock interactions.High speed photography in terms of shadowgraph experiments is used for visualisation. Moreover, an estimation of the fluid velocity on the boundary of the HPWJ in air is performed. For this, the shadowgraph images are evaluated with the double-frame technique well known with particle image velocimetry (PIV). Analysis of both the structure and the velocity distribution of the HPWJ in water is done by combined PIV and laser induced fluorescence (LIF) analysis with fluorescent dye. Keywords PIV, LIF, velocity distribution, jet flow, spray analysis IntroductionThe use of geothermal energy for heat and power exploitation as a renewable energy resource can contribute to a more sustainable energy supply. Enhanced geothermal systems (EGS) enable the recovery of geothermal energy even in surroundings that do not have a naturally hydrothermal system [1,2]. Based on an injection well drilled into hard crystalline rock in up to 3000 m depth, several laterals are drilled into the rock formation to create an EGS.