Abstract
The submerged high-pressure water jet has the characteristics of high velocity, strong turbulence, and severe cavitation. In order to reveal the formation mechanism of shear cavitation in the submerged high-pressure water jet and to grasp the turbulent structure and velocity distribution characteristics in the jet, the prediction ability of different turbulence models is studied first. The models represent the RANS model and RANS-LES hybrid model which are used to simulate the same cavitation jet, and the results are compared with the experimental results. The most reasonable model is then used to investigate the submerged high-pressure cavitation jet with different cavitation numbers. It is found that the calculation accuracy for small-scale vortexes has a great influence on the prediction accuracy of cavitation in the submerged jet. Both the DDES model and the SBES model can effectively capture the vortexes in the shear layer, and the SBES model can obtain more turbulence details. The result of the simulation under different cavitation numbers using the SBES model agrees well with the experimental result. Under the condition with low cavitation number, an intensive shear layer is formed at the exit of the nozzle, and small-scale vortexes are distributed along the shear layer. Mass transfer rate is relatively high in the region with a stronger vortex, which confirms that the low pressure in the vortex center is the main reason for the generation of cavitation in the shear layer. With the decrease of the cavitation number, the cavitation intensity increases obviously, while the nondimensional velocity along the radial direction changes little, which follows an exponential function.
Highlights
In recent years, with the implementation of energy-saving and environmental protection policies, the traditional cleaning technology for large-scale equipment with high pollution such as shot blasting is gradually eliminated. e high-pressure water jet cleaning technology has the characteristics of good processing quality, high efficiency, and environmentally friendly, which is gradually applied to the cleaning process of large-scale marine and chemical equipment [1].e submerged high-pressure water jet is commonly accompanied by intensive cavitation; when the cavitation number is low and the bubble concentration is high, it is difficult to accurately measure the internal flow field by means of PIV or LDV. erefore, it is of great significance to develop the numerical simulation technology of the submerged high-pressure water jet
The main problems to be solved include mass transfer, turbulence, and compressibility. e mass transfer problem mainly corresponds to the modeling of cavitation dynamics. e turbulence problem is related to the accurate prediction of vortexes of various scales in the submerged jet, while compressibility will affect the periodic growth of cavitation unsteady characteristics such as shedding and collapse [10]
Effect of Turbulence Models and Mesh. e choice of the turbulence model determines the accuracy of the velocity field, pressure field, velocity and pressure pulsation, and other physical quantities. erefore, it is necessary to select a suitable turbulence model before conducting numerical simulation studies of cavitation jets. is paper uses the time-average model (RANS) and two hybrid models (RANSLES) to simulate high-pressure water cavitation jets. e simulated boundary conditions are set according to the experimental conditions. e inlet pressure of the highpressure pipeline is set to 20 MPa, and the corresponding cavitation number is σ 0.005
Summary
With the implementation of energy-saving and environmental protection policies, the traditional cleaning technology for large-scale equipment with high pollution such as shot blasting is gradually eliminated. e high-pressure water jet cleaning technology has the characteristics of good processing quality, high efficiency, and environmentally friendly, which is gradually applied to the cleaning process of large-scale marine and chemical equipment [1]. Cheng et al [15] proposed a new Euler–Lagrange cavitation model based on the Rayleigh– Plesset (R-P) equation, taking into account the noncondensable gas In this model, the Euler method is used to solve the global flow field, and the Lagrangian method is used to track the migration of noncondensable gas bubbles into the vortex core. In the case of high-pressure submerged jet, especially when intensive cavitation occurs, the turbulence model has a great effect on the prediction accuracy of the mass transfer phenomenon, while the research on the relation between the turbulence model and the cavitation formation process in the high-pressure submerged jet is lacking. By analyzing the relation between the small-scale vortex and the cavitation formation, the probability for these models to simulate the high-pressure cavitation jet with strong shear stress is discussed. e mechanism and the characteristics of the vortex and cavitation cloud evolution process of the submerged highpressure jet are revealed
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