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 quality of spray reconstruction was investigated using experimental data from multiple view shadowgraphs of hollow cone and flat fan water sprays. After calibration and determination of a 3-D mapping function for each view a line-of-sight (LOS) intensity reconstruction was implemented. After sequential combination of back-projected images at each voxel plane of the volume the 3-D droplet and ligament positions can be readily obtained. Further improvement of intensity reconstruction may be achieved by a iterative tomographic reconstruction, namely multiplicative algebraic reconstruction technique (SMART). These improvements are documented by comparing slices of the averaged 3-D shadowgraph intensity of the hollow cone spray orthogonal to the flow. The investigations were further substantiated with simulations using synthetic data to estimate reconstruction quality at increasing droplet densities.