Deducing Drop Size and Impact Velocity from Circular Bloodstains

Hulse‐Smith, Lee; Mehdizadeh, Navid Z.; Chandra, Sanjeev

doi:10.1520/jfs2003224

Cited by 70 publications

(143 citation statements)

References 13 publications

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“…This model predicts D max =D 0 ∝ We 1=4 , which has been reported in experiments [20,21,24] but sharply contrasts with the energy-conservation (EC) argument. In the forensic literature, even more complicated models attempt to obtain the impact velocity from the number of spines visible around the bloodstain [25][26][27] or by taking the splashing behavior of blood droplets into account [28]. These methods introduce multiple empirical constants, which severely limits their applicability.…”

Section: Introductionmentioning

confidence: 99%

Maximum Diameter of Impacting Liquid Droplets

et al. 2014

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The maximum diameter a droplet that impacts on a surface will attain is the subject of controversy, notably for high-velocity impacts of low-viscosity liquids such as water or blood. We study the impact of droplets of simple liquids of different viscosities, and a shear-thinning complex fluid (blood), for a wide range of surfaces, impact speeds, and impact angles. We show 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, allow for a universal rescaling. The results for different impact angles can be rescaled on this universal curve also, by doing a simple geometrical correction for the impact angle. For blood, we show that the shear-thinning properties do not affect the maximum diameter and only the high-shear rate viscosity is relevant. With our study, we solve a longstanding problem within the fluid-dynamics community: We attest that the spreading behavior of droplets is governed by the conversion of kinetic energy into surface energy or dissipated heat. Energy transfer into internal flows marginally hinders droplet spreading upon impact.

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Section: Introductionmentioning

confidence: 99%

Maximum Diameter of Impacting Liquid Droplets

et al. 2014

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“…the ratio of the maximum contact diameter over the initial drop diameter. The spread factor has been estimated using first-order FD models [13,[112][113][114]. These models compare the various energy terms available before impact (kinetic, potential, surface) with energy terms available after impact, considering that some of the impact energy has been dissipated by e.g.…”

Section: Normal Impactmentioning

confidence: 99%

“…Reference [114] proposes to combine equations (8) and (9) A derived approach, independent of the physical properties of the blood, is described in [107] for impacts on paper, drywall and wood. Spines can merge or be indistinguishable from oscillations on the edge of the stain due to local changes of substrate roughness or wettability.…”

Section: Normal Impactmentioning

confidence: 99%

“…promote splashing. Studies [89,114] compare blood drop impact on different substrates (glass, paper, steel and wood), with different roughness. Note also that a specific class of target surfaces is of specific importance for BPA: the clothes of either the perpetrator or the victim [120].…”

Section: Normal Impactmentioning

confidence: 99%

“…Several recent publications on the impact of blood drops have related the outcomes (spine formation, stain diameter and shape) to impact conditions within a dimensionless framework [11,14,114]. For example, Adam [14] proposed that the observed impact behavior of blood droplets (i.e.…”

Section: W/l= Sinmentioning

confidence: 99%

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

Attinger

Moore

Donaldson

et al. 2013

Forensic Science International

154

139

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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.

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