High-pressure water jets bear a great technological potential to enhance geothermal deep drilling. Compared to existing water cutting technologies, significantly different operation conditions are encountered under deep-drilling conditions, such as high ambient pressures. The fundamental fluid mechanics are significantly affected by those operation conditions. In this work we examine the influence of increasing ambient pressure of up to 12.0 MPa on the water jet characteristics under submerged drilling conditions. PIV measurements of the jet flow field at changing cavitation numbers reveal two characteristic regimes, which are distinguished by a critical cavitation number. In the cavitating regime, the jet decays considerably faster with increasing distance to the nozzle than in the non-cavitating regime. In addition to that, an increasing cavitation intensity shortens the potential core length of the water jet and increases the jet spreading angle and with this has a similar effect on the jet as increasing turbulence intensity in single-phase flows. Related to the decreasing kinetic energy of the jet in the cavitating regime, the resulting impact force of the water jet on the specimen surface decreases with increasing cavitation intensity. Our investigations indicate that a technology transfer from water jet cutting to submerged jet drilling requires adjustments of both nozzle geometries and jet operation conditions.

Graphic abstract

中文翻译：

---

在高压环境下对高雷诺数淹没式水射流的PIV研究

高压水射流具有巨大的技术潜力，可增强地热深层钻探。与现有的水切割技术相比，在深钻条件下（例如高环境压力）会遇到截然不同的操作条件。这些操作条件会极大地影响基本的流体力学。在这项工作中，我们研究了在水下钻井条件下，环境压力升高至12.0 MPa对喷水特性的影响。空化数变化时的射流流场的PIV测量显示出两个特征状态，这两个特征以临界空化数来区分。在空化状态下，与非空化状态相比，射流随着距喷嘴距离的增加而衰减更快。在此之上，空化强度的增加会缩短水射流的潜在核心长度，并增加射流的扩散角，并且对射流的作用与单相流中湍流强度的增加类似。与在空化状态下射流的动能下降有关，水射流在试样表面上产生的冲击力随空化强度的增加而减小。我们的研究表明，从水射流切割到潜水射流钻井的技术转移需要调整喷嘴的几何形状和射流运行条件。与在空化状态下射流的动能下降有关，水射流在试样表面上产生的冲击力随空化强度的增加而减小。我们的研究表明，从水射流切割到潜水射流钻井的技术转移需要调整喷嘴的几何形状和射流运行条件。与在空化状态下射流的动能下降有关，水射流在试样表面上产生的冲击力随空化强度的增加而减小。我们的研究表明，从水射流切割到潜水射流钻井的技术转移需要调整喷嘴的几何形状和射流运行条件。

图形摘要