Pattern Identification on the Nonlinear Radial Motion of an Oscillating Spherical Bubble Using Neural Networks

et al. 2018

Ind. Eng. Chem. Res.

An improved cavitation model was proposed to simulate the cavitation phenomenon in a water jet added with turbulent drag-reducing additives. The Cross model which expressed the shear-thinning properties of drag-reducer solution was also employed. The neglected viscous term and surface tension term in traditional cavitation models were reconsidered as viscosity, and surface tension force were important factors affecting bubbles' motion in drag-reducer solution. The numerical solutions of bubble radius in dragreducer solutions of different concentrations were fitted, and the change rates were added to the original mass transfer mechanism equations. The results showed that the modified cavitation model described the cavitation characteristics in drag-reducer solutions more accurately and effectively reflected that the cavitation region's wake became longer with the increase concentration of the drag reducing agent. When the concentration increased, the distribution of cavitation cloud became more homogeneous, and the pressure curve and velocity curve both changed more smoothly.

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Section: Simulation and Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Numerical Study on Cavitation Generation in a Water Jet Added with Turbulent Drag-Reducing Additives Based on Improved Cavitation Model and Cross Model

et al. 2018

Ind. Eng. Chem. Res.

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“…9, the positive sign is chosen during bubbles' compression process and the negative sign is chosen for the expansion process. According to some scholars' study on the oscillatory motion of a single bubble by a harmonic excitation [26], highly nonlinear responses may be caused on the motion of the bubble as the surrounding liquid may have several degrees of freedom. Some methods (such as the neural networks) have already been used to solve the highly nonlinear equations successfully.…”

Section: Bubble Dynamics and Viscosity Impactmentioning

confidence: 99%

“…Actually, the viscosity of fluid works as a damper during the interaction between bubble and liquid which decreases the overall energy of the oscillating bubble [26]. The damping effects are exerted because of the diffusion of linear momentum by the action of the fluid's viscosity.…”

Section: Insteadmentioning

confidence: 99%

“…Albernaz and Cunha [25] studied the nonlinear response of an oscillatory bubble in a complex fluid using a new model considering the extensional viscosity for the viscous contribution. Malvar et al [26] studied the oscillatory motion of a spherical gas bubble immersed in a Newtonian liquid and concluded that the mechanisms that dominate the dynamics of the oscillating bubble are the competition of the acoustic field excitation with surface tension forces and momentum diffusion by the action of the surrounding fluid viscosity. With the development of computational fluid dynamics, many researchers have tried to simulate the viscous fluid fields combining with bubble dynamics.…”

mentioning

confidence: 99%

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Numerical investigation on the orifice cavitating water jet considering the fluid viscosity’s effects on bubbles’ growth and collapse

J Braz. Soc. Mech. Sci. Eng.

2017

The initial radius of bubble t Time ρ m The density of mixture u m The velocity of mixture μ m The viscosity of mixture α The volume fraction of vapor phase ρ v The density of vapor phase u v The velocity of vapor phase R e Mass transfer source term connected to the growth of the vapor bubbles R c Mass transfer source term connected to the collapse of the vapor bubbles n Bubble number density F vap Evaporation coefficient F cond Condensation coefficient ℜ B Bubble radius 1 Introduction Cavitation is a common hydraulic phenomenon in nature, and the collapse of the bubbles will generate a significant force of impact. So, cavitating water jets are widely used in many engineering fields such as cleaning, cutting, mining and improving the fatigue strength of materials [1-5]. Many experiments and simulations have been conducted to investigate cavitating water jets [6-11]. Since the computational fluid dynamics (CFD) was put forward in 1950s, Abstract This paper attempts to investigate the effects of fluid viscosity on cavitation generation. Different from the traditional cavitation models in which the Rayleigh-Plesset equation is simplified neglecting the second-order term and the surface tension force term, the primitive R-P equations with different dynamic viscosity values are solved by mathematical software and numerical solutions are obtained. Then, the method of curve fitting is selected to get the approximate expressions of bubble radius about time. Based on the expressions, the rate of change of bubble radius about time under different viscous conditions can be approximately obtained which will be written as in-house code to enhance the traditional cavitation models by UDFs. Numerical simulations of high-speed water jets issuing from a nozzle are carried out. The simulated cavitation characteristics match the supercavity experiments very well. The result shows a more homogenous distribution of vapor volume fraction while the viscosity of fluid increases. The pressure and velocity also change more slowly and smoothly along the nozzle under more viscous conditions. Simulations of external flow fields are also made based on the modified model to show the cavitation characteristics under submerged condition.

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Numerical analysis on cavitation effects in submerged water jet added with turbulent drag-reducing additives of CTAC

Chemical Engineering Science

et al. 2019