Enhanced-resolution of flow kinematics from volumetric PTV measurements*

Volumetric, 3D particle tracking velocimetry (PTV) is a nonintrusive technique for flow field measurements. Our previous study (Michael Fenelon, et al. 2023) developed a kinematic decomposition method on the unstructured Lagrangian data obtained from volumetric, 3D PTV using a 4-pulse system version. That method discretizes the domain using Delaunay triangulation, generating triangular and tetrahedral elements for the two and three-dimensional cases, respectively. In the current study, we demonstrate a different approach for the kinematic decomposition, using a specified number of nearest neighboring particles to form unstructured elements. The significant difference between the current approach and Delaunay triangulation is the overlapping of the elements. In numerical simulations, meshed elements are distinct and do not intersect with neighboring ones. In the new method, neighboring elements are permitted to intersect to enhance the resolution of the kinematic decomposition method.  Unlike the Delaunay triangulation, the current method leverages connectivity between nearest neighbors to make the elements smaller than the Delaunay elements. As a result, the overlapped element increases the spatial resolution. We also evaluate the uncertainty associated with the current method and compare it with those using the Delaunay method.