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Laser absorption tomography is an imaging technique used to monitor gas flow and combustion processes. The measurement plane is typically discretized using square pixels in which the flow field is assumed to be uniform. This approach can introduce large discretization errors compared to a finite element mesh with linear interpolation, especially when the domain has an irregular and non-rectangular boundary. In this work, we assess the influence of triangular mesh and quadrilateral mesh schemes on reconstruction accuracy. Our theoretical analysis and numerical studies demonstrate that linear interpolation yields superior performance compared to the conventional uniform-pixel method, and the error can be reduced from 0.250 to 0.097 and 0.160 to 0.105 for triangular and quadrilateral meshes, respectively. Non-body-fitted mesh can increase error by 70 % –99 %. The experiment also proves the superiority of body-fitted meshes with linear interpolation. Moreover, triangular mesh exhibits better noise immunity than quadrilateral mesh. The reconstruction quality appears to be insensitive to the mesh quality for the quadrilateral mesh. [ABSTRACT FROM AUTHOR]

Azimuthally forced spinning modes on a single ethylene-air swirl flame in an annular combustor were investigated using phase-averaged three-dimensional (3D) Computed Tomography of Chemiluminescence. Strongly spinning azimuthal modes in the clockwise (CW) and anticlockwise (ACW) directions were introduced by means of carefully controlled acoustic forcing. Tomographic reconstructions were calculated based on 25 independent views for an unforced, and CW and ACW forced cases. Using only a single flame in an annular enclosure resulted in a flame shape that differed from previous multi-flame investigations. The flame experiences significantly less flame-wall and no flame-flame interactions. Results at high and low equivalence ratio indicate that in the absence of significant enclosure effects, the global heat release rate (HRR) response is the same for both forcing directions. The 3D HRR oscillation distributions were investigated in detail, and the local flame response to modes with opposite spin direction was shown to feature 180 ∘ rotational symmetry. High magnitude HRR oscillations are formed close to the flame base, but due to the combined azimuthal and axial excitation the response on one side of the flame is significantly higher in magnitude, and concentrations of HRR oscillations are seen close to the inner or outer annular walls during CW or ACW excitation respectively. Swirl also causes these high magnitude structures to rotate slowly with downstream distance, although the spatial redistribution of HRR oscillations through this effect is subtle. This improves our physical understanding of previous observations of differing global flame responses to CW and ACW azimuthal excitation. [ABSTRACT FROM AUTHOR]