Abstract

Laser tomography is an optical diagnostic technique based on multiangular absorption spectroscopy. The technique allows the rapid measurement of both species concentration and temperature throughout a 2-D or 3-D nonuniform flow field. This is accomplished by measuring absorption along M equally spaced parallel beams and N equally spaced angles, forming an M × N data set from which the property field (temperature and/or concentration) is reconstructed. The reconstruction is achieved by using Fourier transform, convolution, or maximum entropy techniques. Measurements of OH radical concentration and translational temperature have been carried out in an axisymmetric premixed methane/air flame, using a single measurement angle. The technique has now been extended to a six-angle system, where simultaneous measurements can be made at all six angles at repetition rates up to 10 kHz. Data have been obtained on the dynamics and the 3-D structure of large eddies formed in an ethane/air turbulent diffusion flame. The frequency of eddy formation is controlled by introducing fluctuations into the fuel stream, using a loudspeaker. Formation, shedding, and breakup of eddies, marked by the soot particles formed in the flame, can be observed in detail using the laser tomography technique.

© 1986 Optical Society of America