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The Fluid Dynamics of Droplet Impact on Inclined Surfaces With Application to Forensic Blood Spatter Analysis

NCJ Number
251439
Date Published
January 2017
Length
30 pages
Agencies
NIJ-Sponsored
Annotation
The purpose of this project was to determine whether an analysis of a bloodstain pattern left on a surface can determine the initial size, speed, and impact angle of the blood droplet that left the bloodstain pattern.
Abstract
The project partially completed the development of a numerical simulation of the droplet impact problem. When completed, this will be a time-dependent, three-dimensional, multiphase flow simulation based on a wavelet adaptive grid that was designed using modern computing techniques optimized for fast parallel processing on a single graphic processing unit (GPU). This simulation can accurately predict the motion of a liquid droplet as it impacts and spreads along a solid surface, a typical droplet impact event. The research methodology focused on quantifying the effects of the droplet impact angle, the initial droplet size and speed, and the solid surface roughness and wettabiliity on the pattern of the final observed stain. These data were analyzed to provide simplified, but relevant phenomenological models of droplet impact, spreading, and splashing that can be directly used by forensic scientists. The project used a specially designed droplet generator to create individual liquid droplets of a specified diameter and velocity. The liquid was a specially prepared mixture of water, glycerin, and alcohol that has the same density, viscosity, and surface tension as human blood. The droplets were propelled against three different solid surfaces (glass, bathroom tile, and paper), which were held at a specified angle from vertical. The droplet impact speed was measured by a pair of photodiodes, and the impact of the droplet against the surface was recorded with a high-speed video camera held normal to the impact surface. 19 figures, 3 tables, 20 references, and a listing of 8 reports that disseminate research findings and methodology
Date Created: December 26, 2017