TY - JOUR
T1 - Hydrodynamics of back spatter by blunt bullet gunshot with a link to bloodstain pattern analysis
AU - Comiskey, P. M.
AU - Yarin, A. L.
AU - Attinger, D.
N1 - Funding Information:
The authors acknowledge financial support from the US National Institute of Justice (Grant No. NIJ 2014-DN,BX,K036). This work was partially funded by the Center for Statistics and Applications in Forensic Evidence (CSAFE) through Cooperative Agreement No. 70NANB15H176 between NIST and Iowa State University, which includes activities carried out at Carnegie Mellon University, University of California Irvine, and University of Virginia. The authors gratefully recognize the help of D. R. Van Ryswyk. Technical assistance of S. Kim and J. Polansky in the hematocrit measurement and acquisition of the blood spatters is gratefully acknowledged.
Publisher Copyright:
© 2017 American Physical Society.
PY - 2017/7
Y1 - 2017/7
N2 - A theoretical model describing the blood spatter pattern resulting from a blunt bullet gunshot is proposed. The predictions are compared to experimental data acquired in the present work. This hydrodynamic problem belongs to the class of the impact hydrodynamics with the pressure impulse generating the blood flow. At the free surface, the latter is directed outwards and accelerated toward the surrounding air. As a result, the Rayleigh-Taylor instability of the flow of blood occurs, which is responsible for the formation of blood drops of different sizes and initial velocities. Thus, the initial diameter, velocity, and acceleration of the atomized blood drops can be determined. Then, the equations of motion are solved, describing drop trajectories in air accounting for gravity, and air drag. Also considered are the drop-drop interactions through air, which diminish air drag on the subsequent drops. Accordingly, deposition of two-phase (blood-drop and air) jets on a vertical cardstock sheet located between the shooter and the target (and perforated by the bullet) is predicted and compared with experimental data. The experimental data were acquired with a porous polyurethane foam sheet target impregnated with swine blood, and the blood drops were collected on a vertical cardstock sheet which was perforated by the blunt bullet. The highly porous target possesses a low hydraulic resistance and therefore resembles a pool of blood shot by a blunt bullet normally to its free surface. The back spatter pattern was predicted numerically and compared to the experimental data for the number of drops, their area, the total stain area, and the final impact angle as functions of radial location from the bullet hole in the cardstock sheet (the collection screen). Comparisons of the predicted results with the experimental data revealed satisfactory agreement. The predictions also allow one to find the impact Weber number on the collection screen, which is necessary to predict stain shapes and sizes.
AB - A theoretical model describing the blood spatter pattern resulting from a blunt bullet gunshot is proposed. The predictions are compared to experimental data acquired in the present work. This hydrodynamic problem belongs to the class of the impact hydrodynamics with the pressure impulse generating the blood flow. At the free surface, the latter is directed outwards and accelerated toward the surrounding air. As a result, the Rayleigh-Taylor instability of the flow of blood occurs, which is responsible for the formation of blood drops of different sizes and initial velocities. Thus, the initial diameter, velocity, and acceleration of the atomized blood drops can be determined. Then, the equations of motion are solved, describing drop trajectories in air accounting for gravity, and air drag. Also considered are the drop-drop interactions through air, which diminish air drag on the subsequent drops. Accordingly, deposition of two-phase (blood-drop and air) jets on a vertical cardstock sheet located between the shooter and the target (and perforated by the bullet) is predicted and compared with experimental data. The experimental data were acquired with a porous polyurethane foam sheet target impregnated with swine blood, and the blood drops were collected on a vertical cardstock sheet which was perforated by the blunt bullet. The highly porous target possesses a low hydraulic resistance and therefore resembles a pool of blood shot by a blunt bullet normally to its free surface. The back spatter pattern was predicted numerically and compared to the experimental data for the number of drops, their area, the total stain area, and the final impact angle as functions of radial location from the bullet hole in the cardstock sheet (the collection screen). Comparisons of the predicted results with the experimental data revealed satisfactory agreement. The predictions also allow one to find the impact Weber number on the collection screen, which is necessary to predict stain shapes and sizes.
UR - http://www.scopus.com/inward/record.url?scp=85035344958&partnerID=8YFLogxK
U2 - 10.1103/PhysRevFluids.2.073906
DO - 10.1103/PhysRevFluids.2.073906
M3 - Article
AN - SCOPUS:85035344958
VL - 2
JO - Physical Review Fluids
JF - Physical Review Fluids
SN - 2469-990X
IS - 7
M1 - 073906
ER -