Monday, 12 November 2018

fluid dynamics - Bulk transport of an aerosol by a blast wave


I'm trying to model the behaviour of aerosols in response to blast waves. (This is for visual effects.)


Intuitively, if a flare left a smoke trail above a field and then a bomb detonated elsewhere in the field, one would expect the smoke to be dispersed, to a degree varying with the bomb's energy (among other things.)



Studying blast waves, it has come to my attention that the associated overpressures have both a static pressure and a dynamic pressure component, as seen in this graph:


Source: D. R. Richmond


If I understand correctly, static pressure is due to thermodynamic motion while dynamic pressure is due to net motion of the medium.


The dynamic pressure component is fairly easy to understand: it's basically a wind, and figuring out how something moves in response to it should be straightforward.


The static pressure part is more confusing. I'm assuming this is ordinary longitudinal wave propagation without mass transport, similar to sound. Kind of like shoving one person in a lineup and only the 'shove' itself is transmitted.


One thing I find confusing is that static pressure is a directionless (scalar) quantity, so how does a pressurized region transmit energy only in the direction of propagation? Why doesn't the 'shove' just scatter? (I almost asked this as a separate question.)


Rather than worry about it, my first question is, would the static pressure component of a blast wave even effect any bulk transport of an aerosol?




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