### Meeting Abstract

**P3.60** Friday, Jan. 6 **Measuring angular velocity of models in turbulence using Refractive-Index-Matched PIV** *BYRON, Margaret*; VARIANO, Evan; University of California, Berkeley* mbyron@berkeley.edu

We introduce a method that extends the capabilities of quantitative imaging to reveal the kinematics of organisms in turbulent flow. This work focuses on relevance to animals larger than the Kolmogorov lengthscale (η=0.2mm in this case) but small enough that swimming does not dominate transport; however, the technique is broadly applicable across scales and taxa. We manufacture transparent refractive-index-matched models (RIMMs) for use in stereoscopic PIV. Since the transparency of the particles allows a laser light sheet to pass undistorted through both the fluid and solid phases, RIMMs allow an unprecedented level of access to wake structures, boundary layers, and fluid-phase coupling. RIMMs can be inexpensively fabricated into arbitrary shapes via injection-molding of hydrogels or polymers, and may be varied across many parameters (including size, specific gravity, and deformability). We obtain 3-component velocity fields around differently shaped RIMMs, which are tumbled in homogeneous isotropic turbulence of Re_{λ}=370 (where λ is the Taylor microscale). We then calculate for the first time the rotational dynamics and angular velocity statistics of idealized morphologies (spheres and prolate ellipsoids), using a nonlinear optimization method to solve the solid-body rotation equation. We apply Lagrangian particle-tracking methods to solve for the autocorrelation timescale, quantifying the rotational forcing experienced by organisms in turbulent flow. This information can potentially be used to analyze direction-control behaviors such as station-keeping, righting, or turning. This technique can be applied to large volumes and high Reynolds numbers without difficulty or expense, opening new areas of investigation previously unavailable with conventional refractive-index-matching methods.