Simulations of Blood Drop Spreading and Impact for Bloodstain Pattern Analysis

Bloodstain pattern analysis (BPA) in forensic science is an important tool to solve crime scenes. The complex dynamic behavior of blood drops poses great challenges. for accurate fluid dynamic simulations. In this paper, we specifically focus on simulations of blood drop spreading and impact, which may involve contact line hysteresis and spattering of drops as they interact with solid surfaces. Here, we set up a numerical framework that combines (1) the connectivity-free front tracking (CFFT) method for modeling multiphase (air and liquid) flows and (2) a dynamic contact line model for modeling fluid-solid contact line. Both components are necessary in simulating drop spreading and impact which involve the prediction of the contact line movement and drop spattering. The "connectivity-free" approach refers to the explicit representation of the drop interface points without logical connectivities, which relieves the maintenance and bookkeeping of the interface when the topology goes through large changes as a drop impacts onto a solid surface. It also provides a direct means to couple the dynamic contact line model to form initial contact line and track the contact line movement without reconnecting the points on the interface. Drop spreading and moving on horizontal and oblique planes are studied to show the accuracy and the capability of this coupled algorithm to handle contact line problems. To further validate the method, a drop impacting on a solid obstacle is also performed to demonstrate the flexibility and robustness of the method.