3D Scalar Velocimetry using scanning LIF experiments for counter-swirling coaxial jets.

This work visualizes and measures the flow of two counter-swirling coaxial jets with a scanning Laser-Induced Fluorescence (LIF) setup. The flow is generated by a single-piece coaxial nozzle that has been designed and 3D printed in-house with photocurable polymer resin. The outer jet has an external diameter of 20 mm with a clockwise helical structure while the inner jet diameter is 10 mm with a counter-clockwise helical structure from a top view perspective. Separate gravity-driven water flows feed the two concentric nozzles which have a helical pitch of 200 mm. Two centrifugal pumps inject a solution of Pyranine dye for each jet and the measurement volume is illuminated by a blue laser sheet scanning LIF setup. The laser sheet scanning setup comprises a galvanometer and a set of optics to generate a collimated laser sheet that scans through the volume orthogonally with respect to a High-speed camera. The laser sheet is synchronized and pulsed with a High-Speed video camera (Phantom V2511). The camera is equipped with a bandpass filter to only visualize the emitted dye fluorescence. We processed the recorded images to reconstruct a series of instantaneous 3D scalar fields in real world coordinates. Direct correlation of the volumes in 3D allows us to obtain dense 3D-3C velocity fields for turbulence characterization of this flow.