Has anyone here studied cavitation? (acoustic streaming)

[rwooduk]

Hi,

I am trying to distinguish the mechanisms for acoustic and quasi acoustic streaming during cavitation.

This is what I have written so far:

Quasi acoustic streaming may be described as being due to the existence of an energy gradient in the direction of propagation of the sound field, thus a macroscopic (accelerating) flow develops in its direction.

Acoustic streaming, although inducing some flow, can be said to be a localised phenomenon near to the individual bubbles due to the thermal and mass concentration gradient at the bubbles surface and consequent transfer of the bubbles constituents to the fluid

Quasi acoustic streaming that tends to occur at higher frequencies and acoustic streaming that can occur at both low and high frequencies but has more of an influence at higher powers.

I have the quasi acoustic streaming pretty much sorted, it's just as a result of macroscopic applied frequency effects (flow) from the transducer. Its the acoustic streaming I'm struggling with! Is it like I have written above a direct result of bubble surface fluctuations?

For example for a bubble near a surface we have a boundary streaming effect with causes the bubble to collapse at the surface, which is a direct result of asymmetry of flow near the surface... BUT what is the assymetry of flow due to? The oscillations of the bubble?

I'm trying to figure out what exactly is causing this streaming in a cavitational environment.

Thanks for any ideas!

 

[rwooduk]

ahhh its ok I found it

In the ‘‘genuine acoustic streaming’’, the
fluid motion is produced by the attenuation of the
acoustic wave during its propagation. In the ‘‘quasi-
acoustic streaming’’, fluid motion results from the gradi-
ent of the mean acoustic pressure, as a consequence of
nonlinear phenomena in the ultrasonic wave propaga-
tion.

edit errr maybe not, attenuation of the acoustic wave by what?

edit its okay, please feel free to delete this thread, it appears to be a result of a gradient of acoustic radiation pressure which results in a driving force. i was getting confused with the jetting effect due to boundary flow at an extended surface.

edit but, the bubble motion does influence the fluid due it its viscosity

 

[rwooduk]

ok I've updated my writing on this, hopefully its now correct, here for anyone interested:

Acoustic streaming may be described as being due to the existence of an energy gradient in the direction of propagation of the sound field, thus a macroscopic (accelerating) flow develops in its direction [124-126]. Aside from influencing bubble dynamics this type of streaming also reduces the degree of reflection and distorts the standing wave component of the sound field [127]. Quasi acoustic streaming, although inducing some flow, can be said to be instigated locally near to the individual bubbles due to the thermal and mass concentration gradient at the bubbles surface and consequent transfer of the bubbles constituents to the fluid [128]. The motion of the bubbles is acted upon by radiation pressure, pushing them away from the radiation source, due to viscosity of the fluid an intermittent liquid flow occurs, with bubbles experiencing an approximate exponentially decreasing velocity at both high and low frequencies [123]. This can be said to be more prevalent upon a more violent collapse such as would be seen during sonoluminescence when there is more vigorous volume change and mass transfer [129]. The effect of the motion of bubbles (and hence liquid locally) realising quasi acoustic streaming can also explain the formation of jets (inward collapse of the bubble with jets formation on the proximal side targeted towards a nearby extended surface [16]), caused by asymmetry of flow near the surface [130].