The objective of forensic blood spatter analysis is to use the observed size and shape of a bloodstain to infer the impact conditions of a blood droplet, i.e., its impact angle, impact speed, and size. The goal of this research was to provide a rigorous scientific study of the fluid dynamics of droplet spreading to support the reconstruction techniques used in a blood spatter analysis.
This research was a combined experimental and numerical study of the motion of a liquid droplet with the density, viscosity, and surface tension of blood impacting an inclined planar surface of well-defined roughness and wettability. The main research goals were to: a) quantify the effects of the initial droplet size, speed, and impact angle, and the surface roughness and wettability on the final observed fully spread droplet-shape patterns over a broad range of parameters appropriate to forensic science; and b) analyze these data to provide simplified, but relevant phenomenological models of droplet spreading and splashing that can be directly used by practitioners in the field of forensic science to predict droplet impact parameters using simple bloodstain measurements.
The experimental work resulted in the successful design and build of an acoustically actuated droplet generator. The numerical work produced a numerical simulation of high-speed droplet impact and spreading over a solid surface. The simulation was written using OpenFoam, an open source Computational Fluid Dynamics code. This three-dimensional, time-dependent simulation assumes symmetry about the midplane and uses the appropriate fluid properties for a Newtonian blood simulant.