Small-Scale Morphological Features on a Solid Surface Processed by High-Pressure Abrasive Water Jet
Being subjected to a high-pressure abrasive water jet, solid samples will experience an essential variation of both internal stress and physical characteristics, which is closely associated with the kinetic energy attached to the abrasive particles involved in the jet stream. Here, experiments were performed, with particular emphasis being placed on the kinetic energy attenuation and turbulent features in the jet stream. At jet pressure of 260 MPa, mean velocity and root-mean-square (RMS) velocity on two jet-stream sections were acquired by utilizing the phase Doppler anemometry (PDA) technique. A jet-cutting experiment was then carried out with Al-Mg alloy samples being cut by an abrasive water jet. Morphological features and roughness on the cut surface were quantitatively examined through scanning electron microscopy (SEM) and optical profiling techniques. The results indicate that the high-pressure water jet is characterized by remarkably high mean flow velocities and distinct velocity fluctuations. Those irregular pits and grooves on the cut surfaces indicate both the energy attenuation and the development of radial velocity components in the jet stream. When the sample is positioned with different distances from the nozzle outlet, the obtained quantitative surface roughness varies accordingly. A descriptive model highlighting the behaviors of abrasive particles in jet-cutting process is established in light of the experimental results and correlation analysis.
Large eddy simulation of self-oscillation pulsed water jet drawing in annulus fluid
It is of great significance that developing new rock breaking drilling technology to promote efficient exploit of oil field. High pressure water jet drilling technology is an important method to promote the rock breaking drilling efficiency, and pulsed water jet is such a kind of high efficiency water jet. In order to take full advantage of hydraulic energy in bottom hole, a concept of new type of pulsed water jet drawing in annulus flow, is put forward. The pulsed water jet modulation tool is designed based on the self-exciting principle, and the large eddy simulation is adopted to simulate the flow field and the dynamic characteristics in this tool. This simulation shows the modulation mechanism of self-exciting pulsed water jet drawingin annulus flow. Partial negative pressure could be achieved in the oscillating cavity if the reasonable hydraulic structure is applied. The negative pressure formed in the drawing entrance of the oscillating cavity provides assurance to automatically draw enough fluid into annulus flow, which takes part in modulating the efficient pulsed water jet. The amplitude is larger and the rock breaking capacity of the pulsed water jet drawing in annulus flow is much better than the case non-drawing in annulus flow. The simulation results are verified by the lab experiment. The above research lays the foundation for the development of drilling tools and related technology.
Neurorehabilitation: A Disciplined Disciplining Discipline
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