Abstract

For investigative purposes, the bloodstain pattern analyst might have to estimate whether a given stain on fabric could have originated from a specific location. A wide range of values of the maximum distance that a blood drop can travel have been reported based on experiments, ranging from less than 1 m to more than 10 m. It is also known that stains on porous materials such as fabrics are more difficult to interpret than stains on non-absorbing surfaces, because of wicking. Here, we perform several fluid dynamic spatter experiments and formulate a fluid dynamics model to describe the trajectories of the blood drops. The experiments are performed with swine blood, the properties of which are well understood. The main parameters screened are the drop size, initial velocity, the launch angle, and the orientation of the fabric. A large number of blood drops are produced by impact events. The resulting stains on knitted white T-shirt fabric are digitally measured. Their position relative to the source and size is reported. Trajectories are simulated accounting for the influence of gravity and drag forces. A simple relation between drop size and stain size is established based on extensive experiments on a specific fabric. Results of the trajectory simulations are then searched and mined for parameters directly measurable on a crime scene, such as the stain size on fabric and the relative location of the fabric with respect to the blood source. The experimental results are compared and found in agreement with the numerical predictions. The results are presented in one chart relevant to crime scene reconstruction. The chart is easy to use and only requires minimum knowledge of fluid dynamics.

Graphic abstract

中文翻译：

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从血液来源可以发现织物上的血迹污渍有多远的实验研究，以及与犯罪现场重建的相关性

摘要

出于调查目的，血迹图分析人员可能必须估计织物上的给定污渍是否可能源自特定位置。根据实验报道，血滴可以传播的最大距离的值范围很广，范围从小于1 m到大于10 m。还已知的是，由于芯吸作用，与非吸收性表面上的污渍相比，诸如织物之类的多孔材料上的污渍更难以解释。在这里，我们进行了几次流体动力学飞溅实验，并建立了一个流体动力学模型来描述血滴的轨迹。实验是用猪血进行的，其性质是众所周知的。筛选的主要参数是液滴大小，初始速度，发射角度和织物的方向。撞击事件会产生大量的血滴。用数字方法测量在针织白色T恤织物上产生的污渍。报告了它们相对于来源和大小的位置。模拟了轨迹，说明了重力和拖曳力的影响。基于对特定织物的大量实验，可以建立液滴大小和污渍大小之间的简单关系。然后搜索轨迹模拟的结果，并获取在犯罪现场可直接测量的参数，例如织物上的污渍大小以及织物相对于血源的相对位置。对实验结果进行了比较，发现与数值预测结果吻合。结果以一张与犯罪现场重建有关的图表显示。

图形摘要