Fiber Kinematics in the Near-Field of a Coaxial Jet

Using particle-laden jets, composite materials having specific properties may be fabricated. Using a coaxial jet that is characterized by two mixing layers, one can manipulate vortex generation by either changing the velocity ratio or the absolute value of the jet exit velocities. Here, nylon fiber kinematics (orientation, translation, tumbling rates) were measured in the near-field flow of a coaxial, water jet (one-way coupling) using high speed, planar particle image velocimetry (PIV). The fibers (length 1.6mm, diameter 52μm) were introduced in the center jet. Measurements were performed at three different ratios between outer and inner jet exit velocities, r_u = 0,1,2.5. In addition, the effect of increasing the jet exit velocities was investigated for r_u = 1. Combined PIV and particle tracking velocimetry (PTV) data processing was done for the water velocities and fibers, respectively. Results indicate that fiber rotation is affected by large vortical structures of similar size as the fiber's length. The change in fiber orientation is especially pronounced at the point where the fiber becomes exposed to the inner shear layer. We will discuss both single fiber kinematics as well as orientation statistics in different regions downstream of the jet nozzle.