On the implementation of tomographic shadowgraphy for spray diagnostics

Abstract

This contribution introduces 3-D shadowgraphy which is capable of resolving the placement of the liquid phase within a certain spray volume both spatially and temporally. The method is based on a multiple view camera setup and inline illumination provided by current pulsed LEDs. The observed volume is calibrated with a traversed micro target. A comparison is made between several photogrammetric and polynomial least square camera calibration techniques regarding their accuracy in deep volume calibration at magnifications close to 1 : 1. A new calibration method is suggested which derives volume calibration from multiple planar homographies at equally spaced z-planes. After an sequential combination of back-projected images at each voxel plane the 3-D droplet positions can be readily obtained. The quality of spray reconstruction was investigated using experimental data from multiple view shadowgraphs of hollow cone and flat fan water sprays. The investigations were further substantiated with simulations using synthetic data.