The Fluid Dynamics of Forensic Bloodstain Analysis: Droplet Impact on Inclined Surfaces

As submitted by the proposer:

Bloodstain analysis is a technique used in crime-scene reconstruction to help determine the point of origin of a bloodstain, as well as the method of its creation, e.g., dripping, wiping, or low-to-high-speed impact of a blood droplet caused by anything from blunt trauma to cast-off to gunshot wounds. The primary problem of interest in this analysis is to use the pattern left by the impact of a blood droplet on a surface to determine the impacting droplet’s size, speed, and angle of impact.

The proposed research addresses this problem through a study of the spreading of a liquid droplet impacting an inclined planar surface of well-defined roughness and wettability. The focus of this research is on the fluid dynamics associated with this spreading droplet using a coordinated program of laboratory experiments and numerical simulations. The work will examine the influence of multiple parameters associated with the droplet impact on the shape of the droplet at its point of maximum spreading.

The hypothesis is that this point of maximum spread is related to the final, steady-state shape of a bloodstain as seen in a crime scene. The details of the droplet spreading motion will be examined using the principles of fluid dynamics for a wide-range of Reynolds and Weber numbers (droplet size and speed) of direct interest to the forensic study of bloodstains.

The main goals of the proposed work are to: a) quantify the effects of the initial droplet size, speed, and impact angle, and the surface roughness and wettability on the final observed drop-shape patterns over a broad range of parameters appropriate to forensic science; and b) analyze this 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.

Note: This project contains a research and/or development component, as defined in applicable law, and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14).

ca/ncf