Ultra High-Resolution 3-D flow velocimetry using Cross-Scanning Laser-Induced-Fluorescence (XLIF)*

This work leverages the use of two identical LIF scanning setups placed orthogonally to each other.  Each laser sheet scanning system consists of a galvanometer and a set of optics that create a collimated laser sheet, which scans through the measured volume. These scanning sheets are perpendicular to a high-speed video camera.  The use of orthogonal dual scanning XLIF allows us to 3D map the dye scalar structures of the measured flow with high spatial and temporal resolution in all three axes at nearly the same instant.  Therefore, the recorded images are processed to reconstruct a series of instantaneous 3D scalar fields in real-world coordinates. By directly correlating the scalar volumes in 3D, we can obtain high density 3D-3C velocity fields for analyzing the turbulence characteristics of the flow. We apply this technique to a counter-swirling coaxial jet setup to discretize the volume with nearly 573 million voxels of the full scalar volume (45 x 37 x 43 mm³) at every time instant. To demonstrate the velocimetry capabilities of the method, we perform direct correlation of the volumes in time with high overlap to compute nearly one vector per voxel, achieving a final vector pitch of 57.6 µm/vector in all directions, over most of the volume.  Future effort will be focused on inverting the advection-diffusion equation to further refine the velocity measurements.