COMPUTATIONAL SIMULATION OF CAVITATION BUBBLE COLLAPSE

Radim BurdaIM2020

BRNO UNIVERSITY OF TECHNOLOGYDEPARMENT OF FLUID ENGINEERING

Cavitation bubble collapse

Utilization of hydraulic cavitation

Known for negative effects:

efficiency loss, material damage,..

But can be utilized in various fields:

wastewater treatment,

removal of sediments and corrosion,

disinfection,

shock wave lithotripsy,

ceramics grinding,

underwater travel,

and many more..

Simulation setup

2D axisymetric simulation of bubble collapse near solid wall in Ansys Fluent

Pressure function on boundary𝑝 = 𝑝𝑑 − 𝑝𝑎𝑚𝑝𝑠𝑖𝑛(2𝜋𝑓𝑡)

where: R0 = 78,5 μm; Rinf = 165xR0; pd = 180 kPa; pamp = 20 kPa; f = 20 kHz

Simulation models SST k-ω turbulence model

Volume of Fluid multiphase model

Continuum surface force model

PISO velocity-pressure coupling

Cavitation bubble collapse is very fast phenomenon accompanied by high velocity and pressure, thus: Small variable timestep (0,1 μs – 0,01 ns)

No remeshing or mesh morphing

Water assumed as compressible liquid

Bubble assumed as ideal gas

1. Initial bubble 2. Start of the microjet intrusion 3. Microjet impact

4. Bubble splitting 5. Bubble collapse 6. Bubble collapse on solid wall

Pressure field of cavitation collapse

1. Pressure impact on the center of the solid wall and equivalent radius as a function of time (γ0.76)

2. Maximal bubble collapse impact pressure on the center of solid wall as a function of 𝛾

3. Maximal velocity on the axis (microjet)as a function of 𝛾

4. Equivalent radius-time curves for different values of γ

Summary

Cavitation bubble collapse induced by variable pressure field was successfully simulated using the Volume of Fluid approach

Simulation allowed to distinguish between the pressure peak induced by microjet impact and by cavitation bubble collapse, which is of great importance for understanding of the destruction mechanism of cavitation.

Results obtained in this simulation will be used for development of a cavitation erosion model

Further simulations will focus on response of the bubble to stepwise change of the pressure field, which is situation closer to hydrodynamic cavitation.

Acknowledgement

Czech Science Foundation is gratefully acknowledged for supporting the researchunder project 19-10660S “Removal of estrogens from waste water usinghydrodynamic cavitation in combination with advanced oxidation processes”.

References Rudolf, P., Hudec, M., Zubík, P. and Štefan, D. (2012) Experimental measurement and

numerical modeling of cavitating flow in converging-diverging nozzle. EPJ Web of Conferences (25) 01081

Zezulka, Š., Maršálková, E., Pochylý, F., Rudolf, P., Hudec, M. and Maršálek, B. (2020) High-pressure jet-induced hydrodynamic cavitation as pre-treatment step for avoidingcyanobacterial contamination during water purification. Journal of EnvironmentalManagement, 255, pp. 1-7.

Zupanc, M., Kosjek, T., Petkovšek, M., Dular, M., Kompare, B., Širok, B., Blažeka, Ž. and Heath, E. (2013) Removal of pharmaceuticals from wastewater by biological processes, hydrodynamiccavitation and UV treatment. Ultrasonics Sonochemistry 20(4), pp. 1104-1112

Minsier, V. (2010) Numerical simulation of cavitation-induced bubble dynamics near a solid surface. PhD thesis.

Franc, J.-P. and Michel, J.-M. (2006) Fundamentals of Cavitation. Springer.

Images references

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