This study analyzes the influence of nozzle geometry on the vortex and cavitation cloud structures. The differences between the coherent structures of the Helmholtz nozzle, organ pipe nozzle, and venturi nozzle jets are investigated through large eddy simulation. The vorticity transport equation is used to investigate the relationship between the cavitation cloud and diagonal pressure torque terms. The cavitation and vortex structure shedding frequencies of the jets are investigated using the dynamic mode decomposition method. Three distinct stages of the cavitation bubbles are illustrated: priming, expansion, and collapse. The nozzle structure determines the shape of the primary cavitation bubbles. Moreover, turbulent kinetic energy convergence facilitates the maintenance of the coherent structure. Organ pipe nozzle jets have a high peak velocity at the center axis. Their vortex structure only exhibits a stretched state in the downstream and collapses later than the vortex structures of other nozzles. Advantageously, organ pipe nozzles maintain the stability of the coherent structure. The jets generated by the three nozzles have similar static modes. Helmholtz nozzles produce jets with higher energy and periodically shedding small-scale vortex structural modes. These modes are coupled to the static flow field, resulting in quasi-periodic oscillations of the Helmholtz nozzle jets. The periodic oscillation effect of the Helmholtz nozzle jets is superior to that of the other nozzle jets. The high-energy modes of the venturi nozzle jets have anisotropic and small-scale vortex structures. Furthermore, the venturi nozzle jets exhibit good dispersion and cavitation properties. This study provides guidance for the use of jets with different properties in the respective engineering fields.

Pulsed waterjet can break rocks effectively by taking advantage of the water hammer effect, and is thus widely used in mining, petroleum, and natural gas fields. With the aim to further clarify the flow field characteristics of pulsed jets induced by a Helmholtz oscillator, large eddy simulation was conducted under different operating pressures. The velocity distribution, mean flow field, and the coherent structure were examined using the oscillators of different cavity lengths and diameters. The results clearly showed that the major frequency of jet pulsation gradually increased with the increase of operating pressure. A stable periodic velocity core was formed at the outlet of the Helmholtz oscillator, while the external flow field was subjected to periodic impact. As a result, the ambient fluid was strongly entrained into the jet beam. With the increase of the cavity length, the length of the core segment decreased while the energy loss caused by the cavity increased, which was also accompanied by a rapid attenuation of the axial velocity at the jet outlet. The coherent structure of the jet in the oscillator with small cavity diameter was more disordered near the nozzle outlet, and the vortex scale was larger. The effect of cavity diameter can be reflected in the feedback modulation of the jet in the cavity. Compared with the conical nozzle, the length of the core section of the jet was shorter, but the jet had better bunching, a smaller diffusion angle, and better mixing performance. These results provide a further understanding of the characteristics of pulsed water jet for better utilizations in the fields of energy exploitation.

High-speed water jets are widely used in deep mining and the in-depth study of jet characteristics helps to improve drilling efficiency. Three-dimensional Large Eddy Simulation is used to simulate turbulent flows generated by an organ-pipe nozzle. The simulation is validated with existing experimental data and is focused on the evolution and interaction of cavitation bubbles and vortices. Dynamic mode decomposition is performed to extract structural information about the different motion modes and their stability. Results show that the dominant fluid frequency is positively correlated with inlet pressure while unrelated to the divergence angle. Meanwhile, jets’ oscillation is amplified by a large divergence angle, which facilitates the occurrence of cavitation. Results about the flow field outside of an organ-pipe nozzle advance the understanding of the basic mechanism of cavitation jets.

The dredger construction environment is harsh, and the mud concentration meter can be damaged from time to time. To ensure that the dredger can continue construction operations when the mud concentration meter is damaged, the development of a dredger with advantages of low price and simple operation that can be used in emergency situations is essential. The characteristic spare mud concentration meter is particularly critical. In this study, a data-driven soft sensor method is proposed that can predict the mud concentration in real time and can mitigate current marine mud concentration meter malfunctions, which affects continuous construction. This sensor can also replace the mud concentration meter when the construction is stable, thereby extending its service life. The method is applied to two actual construction cases, and the results show that the stacking generalization (SG) model has a good prediction effect in the two cases, and its goodness of fit R² values are as high as 0.9774 and 0.9919, indicating that this method can successfully detect the mud concentration.