Flow Structure Dynamics of Undulated Cylinder Array Configurations*

An experimental study of seal whisker (phocid pinniped vibrissae) inspired undulated cylinders in various array configurations is conducted to compare the structure of the resultant wakes downstream of the arrays. The study is conducted in the Portland State University wind tunnel with a test section of 5 m in length, 1.2 m in width, and 0.8 m in height. The undulated cylinders are 3D-printed geometries scaled to a mean chord length, C, of 33.63 mm, a mean thickness of 17.53 mm, and a length of 720 mm. The arrays comprise nine (3x3) undulated cylinders oriented vertically and include an inline and staggered (streamwise) configuration with a 3C spanwise spacing and 3, 6, and 9C streamwise spacing. The wakes directly downstream of the arrays are characterized by a 6C square particle image velocimetry (PIV) window (streamwise-spanwise), an inflow of 3.7 m/s, and a Reynolds number of 8,600. Momentum and second-order moments are calculated to describe wake behavior and configuration effects. Results are compared to a single undulated cylinder and a comparable smooth cylinder. Streamwise spacing for the staggered array shows minimal impact on downstream wake behavior, while the inline configuration wake deficit significantly increases with closer streamwise spacing. The bio-inspired experimental study has wide-ranging application potential including reduced column vibration, fluid mixing applications, heat transfer control, and behavioral biological research.