I think you have to define better what you mean about "near a wall". Theoretically, a bubble will behavior closer to a spherical bubble if the standoff distance between the bubble and the wall is larger. The absolute value of standoff distance can not give you clear information if you are comparing two different sizes of bubble. Instead, a non-dimensional standoff distance should be used. The best way to normalize the standoff distance is to use the maximum bubble size. I hope this will help.

When the bubble is large, other types of instabilities is governing the motion of the interface.

Look for articles on super-cavitation.

In larger bubbles, the radius of curvature is not single because the surface tension forces are weak compared to other efforts.

Hi,

Thanks for the replies... Sure, I understand that the bubbles will behave very differently if the size is different - mainly due to the influence of the surface tension. My question was if the non dimensional stand-off distance is the same (it's small so we are for sure talking about a micro-jet), and if we manage to make both bubbles collapse in a very similar way (whatever that means), how much will their volume evolution differ from the one predicted by the RP equation.

I was thinking that if the bubble is big the influence of the surface tension is small - hence the shape, which is not spherical, shouldn't play a big role in the time evolution of the volume. Consequently RP prediction is better for big bubbles... Well that's just one of the views. I guess, one also make reasoning the other way around, that is that the surface tension will tend to make the smaller bubble more spherical and that RP eqn. will therefore work better for small bubbles...but then our initial assumption that both bubbles collapse in a similar way doesn't apply any more and we''re back at the beginning.

Dear Matevz, late answer, just joined RG.

The volume dynamics is very well captured with RP, thus RP should work for midly deformed bubbles. This is the case for gamma>1.5 near a surface, the jet forms only in the late phase prior collapse. The rebound with jet can't be captured with RP, because you loose energy during the impact (water hammer pressure) and the formation of a vortex ring. Thus the question remains, RP better for smaller than larger bubbles? It works very well for small (SL type bubbles) and for large ones (under water explosions), yet when the bubble is too large, buoyant effects can came in as the pressure head between top and bottom is large and the oscillation time is larger, thus more time to develop instabilities. My guess therefore is that RP is good for volume dynamics for gamma>1.5 and sufficiently small bubbles.

Hi Dieter,

Thanks for the input. The question actually refered to the work we've published in JFM some time ago. I'm still trying to find time to repeat those experiments in other fluids, at other temperatures...but no luck so far...

Hope to see you again soon!

Matevz