Dye visualization--a method for investigating biomechanical flows

Flow visualization using dye is an inexpensive and easy-to-implement experimental technique. It can be used for a rapid qualitative assessment of fluid flows in configurations relevant to biomedical or biotechnological applications, which often involve small spatial dimensions and flow velocities (low Reynolds numbers). This paper gives an overview of the practical aspects related to dye visualization in liquids (dyes, introduction of dye into the flow, illumination), and discusses the information that can be obtained by this method, which includes the distribution of coherent structures/ vortices, the location of recirculation zones, and certain characteristic spatial and temporal scales. Visualization results for three examples of generic flows related to biomechanical applications are presented: the flow behind a contraction in a pipe (stenosis), the wake of a particle moving along a wall, and the flow inside a lid-driven mixing vessel (bioreactor).