Numerical Study On The Dynamics Of Aspherical Cavitation Bubble In Non-newtonian Purely Viscous Fluids

Cavitation plays a major role in a wide range of applications,from engineering to military and medical,and this research stemmed from a desire to better understand the cavitation dynamics in non-Newtonian purely viscous fluids and their interactions with various boundaries.Although cavitation has been found to occur frequently in nonNewtonian fluids,most studies have only focused on Newtonian fluids.The numerical studies presented in this research attempts to comprehensively examine the dynamics of a cavitating bubble in a purely viscous fluid through numerical calculations.Three models were selected to study the bubble dynamics with respect to a rigid wall,parallel walls and a free surface boundary.On a fixed Cartesian grid,the twodimensional axisymmetric Navier-Stokes equations are solved for both the compressible gas phase,the incompressible and compressible liquid phase.The bubble-liquid interface is tracked by the Volume of Fluid method and the validity of the numerical models were verified by comparing the evolutions of the bubble profile with experimental bubble profiles.0.5% Carboxymethylcelullose solution was modelled with the carreau fluid model as a purely viscous fluid and the bubble dynamics with respect to the various carreau model parameters was analysed in details.Generally,across the three boundaries considered,variations in the stand-off parameter(?)caused significant changes in the bubble dynamics.At very small values of ?,the bubble collapse seemed to have an insignificant effect on the rigid and parallel wall boundaries respectively due to the influence of the rigid walls and at very high values,the bubble collapsed like in free field but for the free surface,the reverse was the case.For the collapse of a single bubble near a rigid wall,higher values of the infinite shear viscosity(?_?),the power law index(n)the surface tension(?)and lower values of the time constant(?)were found to significantly impede the cavitation process.The influence of the zero-shear viscosity(?₀)was found to be negligible across the three various boundaries.For the bubble collapse in between two parallel walls,the collapsing bubble shape and the jet front velocity at different p? were investigated and the bubble collapse was found to be significantly retarded as ?_? increased.During the axisymmetric and asymmetric collapse,higher values of ?₀ and n were found to exacerbate the cavitation process but at higher values of ? and ?,the jet front velocity was found to decrease significantly.For the bubble collapse near a free surface boundary,increasing values of ?_?and? were found to significantly retard the bubble during growth and collaspe while the reverse occurred as the values of ? were increased.The values of n were found to have the same trend as ?_?and ? at ? =0.78 but at ? =1.25,the jet front velocity suddenly spiked at a higher value of n,indicating a decrease in the viscosity of CMC.The bubble dynamics with respect to the various boundaries are fully explored in details in this study.