The Science of Blood
LT4 School of Chemistry
Bloodstain Pattern Analysis is a forensic discipline in which, among others, the position of victims can be determined at crime scenes on which blood has been shed. To determine where the blood source was investigators use a straight-line approximation for the trajectory, ignoring effects of gravity and drag and thus overestimating the height of the source. To include gravity and air drag into the models, the maximum diameter a droplet that impacts on a surface needs to be determined. However for a long time this was subject of controversy, notably for high-velocity impacts of low-viscosity liquids such as water or blood.
I will present our work on the drop impact for simple and complex liquids and show that the controversy can be resolved by understanding that the spreading behavior cannot simply be predicted by equating the inertial to either capillary or viscous forces, since, for most situations of practical interest, all three forces are important. We determine the correct scaling behaviors for the viscous and capillary regimes and, by interpolating between the two, find a universal rescaling. This allows to include gravity and drag in the trajectory calculation of blood drops on the crime scene also; the origin’s location can be determined roughly four times more accurately than with the straight-line approximation.
For further information, contact Ioatzin Ríos de Anda at email@example.com