Tomographic shadowgraphy for three-dimensional reconstruction of instantaneous spray distributions

• Published in: Experiments in fluids Vol. 53; no. 2; pp. 531 - 543
• Main Authors: Klinner, Joachim, Willert, Christian
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.08.2012; Springer
• Subjects: Applied sciences; Calibration; Cameras; Droplets; Energy; Energy. Thermal use of fuels; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Engines and turbines; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fluid dynamics; Fluid- and Aerodynamics; Fundamental areas of phenomenology (including applications); Heat and Mass Transfer; Instrumentation for fluid dynamics; Physics; Planes; Reconstruction; Research Article; Sprayers; Sprays; Three dimensional; Droplet Velocity; Direct Linear Transformation; Particle Tracking Velocimetry; Spray Angle; Liquid Sheet; Motor fuel injection; Combustion chamber; Three dimensional flow; Test facility; Kerosene; Tomography; Calibration; Gas turbine; Experimental study; Pulverized fuel; Image reconstruction; Shadowscopy
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-012-1308-2

Tomographic shadowgraphy is an image-based optical technique capable of reconstructing the three dimensional instantaneous spray distributions within a given volume. The method is based on a multiple view imaging setup with inline illumination provided by current-pulsed LEDs, which results in droplet shadows being projected onto multiple sensor planes. Each camera records image pairs with short inter-framing times that allow the trajectories of the individual droplets to be estimated using conventional three-dimensional particle tracking approaches. 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 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. The combination of back-projected images at each voxel plane efficiently reproduces the droplet positions in three-dimensional space by line-of-sight (LOS) intensity reconstruction. Further improvement of the reconstruction can be achieved by iterative tomographic reconstruction, namely simultaneous multiplicative algebraic reconstruction technique (SMART). 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.