Abstract
This study investigates the effects of wall wettability on cavitation bubble collapse using the pseudopotential lattice Boltzmann method with an appropriate external force term and wall contact angle boundary condition. The accuracy of the proposed numerical approach is verified by simulating a single-bubble collapse near a neutral wall. The result shows that the wettability condition of the wall has a significant effect on the forces exerted on cavitation bubbles. For a hydrophilic surface, there is a repulsive force between the surface and the bubble, whereas for a hydrophobic surface, the force is attractive. The wall wettability affects the evolution of the bubble shape, the maximum collapse pressure, the microjet velocity, and the total kinetic energy of the cavitation bubble during its collapse. Changing the wettability from hydrophobic to hydrophilic decreases the maximum pressure and microjet velocity but increases the cavitation bubble lifetime. Furthermore, the range of wall effects is smaller for a hydrophilic wall than for a hydrophobic wall.
Highlights
Cavitation is widespread in engineering and industrial processes
Bremond and co-workers10–12 conducted a series of experiments and found that hydrophobic surfaces are more prone to cavitation, owing to the ease of formation of micro- and nanobubbles and bubble nuclei on such surfaces and to the fact that the liquid density near a hydrophobic surface is smaller than that near a hydrophilic surface
The results indicate that when Gw < 0, the corresponding contact angle is less than 90○, which means that the wall is hydrophilic
Summary
Cavitation is widespread in engineering and industrial processes. Owing to the dramatic changes in pressure around collapsing bubbles, the gas and liquid phases rapidly transform from one to the other, and the high temperature, microjets, and shock waves generated during the collapse process can have a negative impact on buildings and mechanical structures. Previous studies have shown that there are two ways to reduce cavitation damage: (i) reduce the impact pressure and microjet velocity on the wall during the collapse process, such as by optimizing the flow structure and aeration; and (ii) increase the resistance of the wall material, such as by changing its wettability and reducing its roughness.. All of the above experimental studies focused on the damage to the wall caused by cavitation bubbles, and there has been little research into how different wall properties affect the microjet velocity, shock waves, and collapse pressure of cavitation bubbles. The effects of wall wettability on cavitation bubbles are investigated using the LBM pseudopotential model with the MRT collision operator and the force terms derived by Li et al..
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