20-kHz-rate three-dimensional tomographic imaging of the concentration field in a turbulent jet

Three-dimensional imaging of the tracer concentration field is demonstrated at a rate of 20 kHz in a turbulent gaseous free jet. The acetone tracer species that is seeded into the jet is excited by the fourth-harmonic output of a Nd:YAG burst-mode laser. The laser beam is expanded and re-collimated to a 35-mm-diameter beam and passed through a diffuser to reduce spatial variations within the beam profile. Seven high-speed cameras coupled to high-speed intensifiers with vertical stereoscopes collect fourteen simultaneous views of the fluorescence emission. The images are processed and a linear relationship between signal intensity and acetone concentration was verified. Eight of the fourteen processed views are then reconstructed into volumes using a simultaneous multiplicative algebraic-reconstruction technique, limited by the software. The mixing behavior is characterized and compared with turbulent-jet scaling laws and data from the literature at similar conditions. The accuracy, precision, and limitations of the technique are discussed, and potential strategies for implementation in reacting flows are considered.