Dynamics of blood falling on three types of cotton fabrics and resulting bloodstains.

The time evolution of blood drops falling on plain woven, 3 × 1 twill, and jersey knit cotton fabric were studied. Three time domains were observed; at times less than 0.1 s, the drop travels across the fabric surface, spreading, forming a rim, breaking up of the rim, and retracting. In this domain, the blood drop morphology and the bloodstain area is strongly affected by the impact Weber number (We). Near the end of the first time domain, the blood begins to enter the inter-yarn spaces in the fabric structure, ceases to be an independent drop and begins to spread within the fabric (time domain 2). In a third time domain, blood moves from the inter-yarn spaces into the inter-fiber spaces and wicks along the fiber surfaces within the yarn to form still larger stain patterns. The final stain sizes were nearly independent of the impact We, but strongly dependent on the fabric structure: the stain being the largest on plain woven fabric while smallest on knit fabric. Empirical power-law-based models were developed to predict wicking kinematics, the splashing threshold, and the number of satellite droplets during splashing. Comparison with experimental data demonstrates the model's adequacy in describing wicking kinematics while highlighting its limitations in predicting the splashing threshold and the formation of satellite droplets.