Computed Tomography of Chemiluminescence (CTC): Instantaneous 3D measurements and Phantom studies of a turbulent opposed jet flame

Time resolved 3D measurements are required to further the understanding of turbulent combustion and to support the development of advanced simulation techniques such as LES. The Computed Tomography of Chemiluminescence (CTC) technique reconstructs the 3D chemiluminescence field of a turbulent flame from a series of integral measurements (camera images). The resulting data can be analysed to obtain the flame surface density, wrinkling factor, flame normal direction and possibly heat release rate, and also to study transient phenomena. High resolution CTC requires measurements from many viewing angles, and the capabilities of recent machine vision cameras make this affordable. The present paper investigates CTC using such commodity cameras. CTC is implemented using five PicSight P32M cameras and mirrors to provide 10 simultaneous views of a premixed turbulent opposed jet (TOJ) flame. The reconstructions are then performed using a 3D Algebraic Reconstruction Technique (ART) algorithm. For the flame investigated, camera exposure times of only 250 μs were found to provide more than sufficient signal-to-noise ratios for ART reconstruction with still shorter exposures times possible. All reconstructions capture the main features of the TOJ flame and were found to provide a useful spatial resolution, even with just 10 views. Detailed Phantom studies were performed to assess the resolution available from ART. The resolution was found to be object dependent but a good working estimate was obtained from a relation by Frieder and Herman (1971) [64]. Reconstructions of realistic LES Phantom data have shown that high resolution reconstructions, which resolve wavelengths of 0.035 object diameters, can be a achieved from only 20 views, with each view costing less than $1000.