Experimental validation of a numerical model for predicting the trajectory of blood drops in typical crime scene conditions, including droplet deformation and breakup, with a study of the effect of indoor air currents and wind on typical spatter drop trajectories

Kabaliuk, N.; Jermy, M.C.; Williams, Elisabeth; Laber, T.L.; Taylor, M.C.

doi:10.1016/j.forsciint.2014.10.020

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Experimental validation of a numerical model for predicting the trajectory of blood drops in typical crime scene conditions, including droplet deformation and breakup, with a study of the effect of indoor air currents and wind on...

N. Kabaliuk, M.C. Jermy, Elisabeth Williams

, T.L. Laber, M.C. Taylor

Forensic Science International, Volume: 245, Pages: 107 - 120

Swansea University Author: Elisabeth Williams

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DOI (Published version): 10.1016/j.forsciint.2014.10.020

Abstract

Bloodstain Pattern Analysis (BPA) provides information about events during an assault, e.g. location of participants, weapon type and number of blows. To extract the maximum information from spatter stains, the size, velocity and direction of the drop that produces each stain, and forces acting duri...

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Published in:	Forensic Science International
ISSN:	0379-0738
Published:	2014
Online Access:	Check full text
URI:	https://cronfa.swan.ac.uk/Record/cronfa32277
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spelling	2023-02-02T16:12:01.2274441 v2 32277 2017-03-03 Experimental validation of a numerical model for predicting the trajectory of blood drops in typical crime scene conditions, including droplet deformation and breakup, with a study of the effect of indoor air currents and wind on typical spatter drop trajectories 2c5b3af00392058866bfd4af84bef390 0000-0002-8422-5842 Elisabeth Williams Elisabeth Williams true false 2017-03-03 STSC Bloodstain Pattern Analysis (BPA) provides information about events during an assault, e.g. location of participants, weapon type and number of blows. To extract the maximum information from spatter stains, the size, velocity and direction of the drop that produces each stain, and forces acting during flight, must be known.A numerical scheme for accurate modeling of blood drop flight, in typical crime scene conditions, including droplet oscillation, deformation and in-flight disintegration, was developed and validated against analytical and experimental data including passive blood drop oscillations, deformation at terminal velocity, cast-off and impact drop deformation and breakup features. 4th order Runge–Kutta timestepping was used with the Taylor Analogy Breakup (TAB) model and Pilch and Erdman's (1987) expression for breakup time. Experimental data for terminal velocities, oscillations, and deformation was obtained via digital high-speed imaging. A single model was found to describe drop behavior accurately in passive, cast off and impact scenarios.Terminal velocities of typical passive drops falling up to 8 m, distances and times required to reach them were predicted within 5%. Initial oscillations of passive blood drops with diameters of 1 mm < d < 6 mm falling up to 1.5 m were studied. Predictions of oscillating passive drop aspect ratio were within 1.6% of experiment. Under typical crime scene conditions, the velocity of the drop within the first 1.5 m of fall is affected little by drag, oscillation or deformation.Blood drops with diameter 0.4–4 mm and velocity 1–15 m/s cast-off from a rotating disk showed low deformation levels (Weber number < 3). Drops formed by blunt impact 0.1–2 mm in diameter at velocities of 14–25 m/s were highly deformed (aspect ratios down to 0.4) and the larger impact blood drops (∼1–1.5 mm in diameter) broke up at critical Weber numbers of 12–14. Most break-ups occurred within 10–20 cm of the impact point. The model predicted deformation levels of cast-off and impact blood drops within 5% of experiment. Under typical crime scene conditions, few cast-off drops will break up in flight. However some impact-generated drops were seen to break up, some by the vibration, others by bag breakup.The validated model can be used to gain deep understanding of the processes leading to spatter stains, and can be used to answer questions about proposed scenarios, e.g. how far blood drops may travel, or how stain patterns are affected by winds and draughts. Journal Article Forensic Science International 245 107 120 0379-0738 Bloodstain pattern analysis; Drag; Droplet breakup; Droplet oscillation; Numerical modeling; Trajectory 31 12 2014 2014-12-31 10.1016/j.forsciint.2014.10.020 COLLEGE NANME Sport and Exercise Sciences COLLEGE CODE STSC Swansea University 2023-02-02T16:12:01.2274441 2017-03-03T13:57:20.1877065 Faculty of Science and Engineering School of Engineering and Applied Sciences - Sport and Exercise Sciences N. Kabaliuk 1 M.C. Jermy 2 Elisabeth Williams 0000-0002-8422-5842 3 T.L. Laber 4 M.C. Taylor 5
title	Experimental validation of a numerical model for predicting the trajectory of blood drops in typical crime scene conditions, including droplet deformation and breakup, with a study of the effect of indoor air currents and wind on typical spatter drop trajectories
spellingShingle	Experimental validation of a numerical model for predicting the trajectory of blood drops in typical crime scene conditions, including droplet deformation and breakup, with a study of the effect of indoor air currents and wind on typical spatter drop trajectories Elisabeth Williams
title_short	Experimental validation of a numerical model for predicting the trajectory of blood drops in typical crime scene conditions, including droplet deformation and breakup, with a study of the effect of indoor air currents and wind on typical spatter drop trajectories
title_full	Experimental validation of a numerical model for predicting the trajectory of blood drops in typical crime scene conditions, including droplet deformation and breakup, with a study of the effect of indoor air currents and wind on typical spatter drop trajectories
title_fullStr	Experimental validation of a numerical model for predicting the trajectory of blood drops in typical crime scene conditions, including droplet deformation and breakup, with a study of the effect of indoor air currents and wind on typical spatter drop trajectories
title_full_unstemmed	Experimental validation of a numerical model for predicting the trajectory of blood drops in typical crime scene conditions, including droplet deformation and breakup, with a study of the effect of indoor air currents and wind on typical spatter drop trajectories
title_sort	Experimental validation of a numerical model for predicting the trajectory of blood drops in typical crime scene conditions, including droplet deformation and breakup, with a study of the effect of indoor air currents and wind on typical spatter drop trajectories
author_id_str_mv	2c5b3af00392058866bfd4af84bef390
author_id_fullname_str_mv	2c5b3af00392058866bfd4af84bef390_***_Elisabeth Williams
author	Elisabeth Williams
author2	N. Kabaliuk M.C. Jermy Elisabeth Williams T.L. Laber M.C. Taylor
format	Journal article
container_title	Forensic Science International
container_volume	245
container_start_page	107
publishDate	2014
institution	Swansea University
issn	0379-0738
doi_str_mv	10.1016/j.forsciint.2014.10.020
college_str	Faculty of Science and Engineering
hierarchytype
hierarchy_top_id	facultyofscienceandengineering
hierarchy_top_title	Faculty of Science and Engineering
hierarchy_parent_id	facultyofscienceandengineering
hierarchy_parent_title	Faculty of Science and Engineering
department_str	School of Engineering and Applied Sciences - Sport and Exercise Sciences{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Sport and Exercise Sciences
document_store_str	0
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description	Bloodstain Pattern Analysis (BPA) provides information about events during an assault, e.g. location of participants, weapon type and number of blows. To extract the maximum information from spatter stains, the size, velocity and direction of the drop that produces each stain, and forces acting during flight, must be known.A numerical scheme for accurate modeling of blood drop flight, in typical crime scene conditions, including droplet oscillation, deformation and in-flight disintegration, was developed and validated against analytical and experimental data including passive blood drop oscillations, deformation at terminal velocity, cast-off and impact drop deformation and breakup features. 4th order Runge–Kutta timestepping was used with the Taylor Analogy Breakup (TAB) model and Pilch and Erdman's (1987) expression for breakup time. Experimental data for terminal velocities, oscillations, and deformation was obtained via digital high-speed imaging. A single model was found to describe drop behavior accurately in passive, cast off and impact scenarios.Terminal velocities of typical passive drops falling up to 8 m, distances and times required to reach them were predicted within 5%. Initial oscillations of passive blood drops with diameters of 1 mm < d < 6 mm falling up to 1.5 m were studied. Predictions of oscillating passive drop aspect ratio were within 1.6% of experiment. Under typical crime scene conditions, the velocity of the drop within the first 1.5 m of fall is affected little by drag, oscillation or deformation.Blood drops with diameter 0.4–4 mm and velocity 1–15 m/s cast-off from a rotating disk showed low deformation levels (Weber number < 3). Drops formed by blunt impact 0.1–2 mm in diameter at velocities of 14–25 m/s were highly deformed (aspect ratios down to 0.4) and the larger impact blood drops (∼1–1.5 mm in diameter) broke up at critical Weber numbers of 12–14. Most break-ups occurred within 10–20 cm of the impact point. The model predicted deformation levels of cast-off and impact blood drops within 5% of experiment. Under typical crime scene conditions, few cast-off drops will break up in flight. However some impact-generated drops were seen to break up, some by the vibration, others by bag breakup.The validated model can be used to gain deep understanding of the processes leading to spatter stains, and can be used to answer questions about proposed scenarios, e.g. how far blood drops may travel, or how stain patterns are affected by winds and draughts.
published_date	2014-12-31T03:39:32Z
_version_	1763751779430825984
score	11.035349

Experimental validation of a numerical model for predicting the trajectory of blood drops in typical crime scene conditions, including droplet deformation and breakup, with a study of the effect of indoor air currents and wind on...

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