This study examined self-similar turbulent vortex rings theoretically in the framework of the semi-empirical turbulence theory for the modified Helmholtz equation.
The velocity and vorticity fields were established, as well as the transport of passive admixture by turbulent vortex rings. Turbulent vortex rings of propellant gases originating from the muzzle of a gun after a gunshot are an important phenomenon to consider in crime scene reconstruction. This work showed that this has a significant repercussion on the outcome of backward blood spatter resulting from a gunshot. Turbulent vortex rings of propellant gases skew the distribution of bloodstains on the ground and can either propel blood droplets further from the target, or even turn them backwards towards the target. This was revealed through the final bloodstain locations and the respective distributions of the number of stains and their area as a function of distance from the target for two different shooter-to-target distances. An image of the propagating muzzle gases after bullet ejection was overlaid with the predicted flow field, which revealed satisfactory agreement. Gunshot residue is an important factor in determining the events of a violent crime due to a gunshot and were considered to be entrained and transported by the propellant gases. The self-similar solutions for the flow, vorticity and concentration of gunpowder particles were predicted, and the results were shown to be within the measured range of a limited set of experimental data. (publisher abstract modified)
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