Time-averaged tomographic absorption spectroscopy for H2O diffusion in turbulent jet flow at room temperature

Abstract

Tomographic absorption spectroscopy (TAS) is important for the combustion diagnostics of hydrogen and hydrocarbon fuels in various flow fields. In this study, we proposed and conducted time-averaged TAS for the reconstructions of mean H2O mole fraction XH2O in a dry, axisymmetric, turbulent jet flow with a Reynolds number of 5670 to reveal the effect of turbulence on absorption spectroscopy measurement. The absorption line of H2O near 1368.598 nm was selected and scanned at 1 kHz. The effect of turbulence on TAS, which is positively related to the turbulent intensity along the optical path, has been confirmed and can be effectively alleviated by conducting time averaging. It is shown that the proper selections of scan rate and the number of time steps for statistical convergence are required for time-averaged TAS. With time averaging and smoothing operations on the integrated absorbance, the two-dimensional mean XH2O distributions were reconstructed with the present method and the result showed a good agreement with CFD simulation. The mean deviation of the measured results can be reduced by over 25% when the number of time steps for average is 30000. The present study highlights the potential of TAS for the visualization and diagnostics of complex flows such as turbulent non-reactive flow and turbulent combustion.