3-D Lokalisierung von Sprays mit tomografischer Schattenfotografie

Abstract

This contribution introduces tomographic shadowgraphy, a volume resolving imaging technique which is capable of recovering the liquid phase of a spray both spatially and temporally. The method is based on a multiple view camera setup with inline illumination provided by current pulsed LEDs which results in droplet shadows being projected onto the sensor plane. Each camera records image pairs with short inter‐framing times which allows the trajectories of the ndividual droplets to be estimated using conventional three‐dimensional particle tracking approaches. The observed volume is calibrated with a traversed micro target. A omparison is made between several photogrammetric and polynomial least square camera calibration techniques egarding their accuracy in deep volume calibration at agnifications close to unity. A calibration method based on volume calibration from multiple planar homographies at equally spaced z‐planes was found to produce the most reliable calibration. Sequential combination of back‐projected images at each voxel plane efficiently reproduces the droplet positions in three‐dimensional space. The quality of spray reconstruction is investigated using experimental data from multiple view shadowgraphs of hollow cone and flat fan water sprays. The investigations are further substantiated with simulations using synthetic data.