Fluid dynamics topics in bloodstain pattern analysis: Comparative review and research opportunities

Abstract

This comparative review highlights the relationships between the disciplines of bloodstain pattern analysis (BPA) in forensics and that of fluid dynamics (FD) in the physical sciences. In both the BPA and FD communities, scientists study the motion and phase change of a liquid in contact with air, or with other liquids or solids. Five aspects of BPA related to FD are discussed: the physical forces driving the motion of blood as a fluid; the generation of the drops; their flight in the air; their impact on solid or liquid surfaces; and the production of stains. For each of these topics, the relevant literature from the BPA community and from the FD community is reviewed. Comments are provided on opportunities for joint BPA and FD research, and on the development of novel FD-based tools and methods for BPA. Also, the use of dimensionless numbers is proposed to inform BPA analyses. Keywordsbloodstain pattern analysis, review, dimensionless number, drop generation, trajectory, impact, stain Disciplines Laboratory and Basic Science Research | Other Mechanical EngineeringComments NOTICE: this is the author's version of a work that was accepted for publication in Forensic Science International. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Forensic Science International, [231, 1-3, (2013) Abstract: This comparative review highlights the relationships between the disciplines of bloodstain pattern analysis (BPA) in forensics and that of fluid dynamics (FD) in the physical sciences. In both the BPA and FD communities, scientists study the motion and phase change of a liquid in contact with air, or with other liquids or solids. Five aspects of BPA related to FD are discussed: the physical forces driving the motion of blood as a fluid; the generation of the drops; their flight in the air; their impact on solid or liquid surfaces; and the production of stains. For each of these topics, the relevant literature from the BPA community and from the FD community is reviewed. Comments are provided on opportunities for joint BPA and FD research, and on the development of novel FD-based tools and methods for BPA. Also, the use of dimensionless numbers is proposed to inform BPA analyses.

Prediction of blood back spatter from a gunshot in bloodstain pattern analysis

“…A sound fluid-mechanical theory of drop atomization, trajectories, and impact would be relevant to the interpretation of blood spatters resulting from gunshot wounds such as the infamous case of Phil Spector, where the question arose of if blood from the back spatter could travel a distance of approximately 1.8 m [2]. Backward reconstruction of drop trajectories is typically based on the inspection of bloodstains and on a model for the flight of drops [3].…”

“…The area of convergence corresponds to the projection of the trajectories on a horizontal plane. To determine the area of origin, bloodstain pattern analysis (BPA) experts use the angle of impact α from several stains using visual inspection [3]. This angle is the acute angle at which a blood drop impacts the deposition surface, e.g., a floor [see Fig.…”

“…There is abundant BPA literature on the uncertainties associated with the choice of stains and their inspection to determine the angle of impact and area of origin, as reviewed in Ref. [3]. The actual trajectories are curved, due to the effect of gravity, which is amplified by the air drag.…”

“…Since ballistic reconstruction involves the knowledge of impact velocity and drop size, a significant amount of recent BPA work has focused on obtaining that information by inspecting the stains, as proposed in Ref. [16]. The authors of [17] reconstructed drop trajectories using ballistic calculations, considering gravity and drag forces, and determined the region of origin with about four times higher accuracy than under the assumption of straight trajectories.…”

Influence of the impact energy on the pattern of blood drip stains

“…Hence, from this solution it is possible to find the impact velocity U as it will alter the maximum spreading ratio, but an initial piece of information, namely, the initial diameter of the droplet or its volume, is required. In order to complete this approach, as well as other approaches that already exist [8][9][10], a different parameter is thus necessary to determine the impact velocity from the final bloodstain. However, it could be assumed that the impact velocity, because of altering the maximum spreading diameter, will have an influence on the drying stage, mainly on the internal flow observed during the first regime and will affect the observed pattern of the drip stain.…”