A Data-Driven Method for Determining the Hydrodynamic Force Induced by Vortices – Force Partitioning Applied to PIV Data for a Caudal Fin Model*

The force partitioning method (FPM) (Zhang et al, PLOS One, 2015 and Menon & Mittal, JFM 2021) enables the partitioning of pressure-induced forces into distinct physical mechanisms/features such as added mass, viscous diffusion, vortices, and shear layers. Previous studies have applied FPM to data generated from flow simulations. In the current study, we demonstrate the first-ever application of this method using flow data from experiments. The experiments involve a model of a fish with a dynamic caudal fin and employ PIV to generate 4D data (3D in space + time) of the flow and vortices generated by the motion of the caudal fin. The fin generates a set of vortices including leading-edge and trailing-edge vortices. While a number of methods exist to extract/measure the total forces on the control surface, quantifying the forces induced by individual vortices is quite difficult. We combine PIV data from the experiments with the data-driven and physics-based FPM framework to quantify the forces induced by individual vortices and demonstrate the power of this method to dissect the flow physics of vortex-dominated flows.