Thermometry in gas flows using two-line fluorescence imaging and structured illumination

Abstract

We present a feasibility demonstration of the instantaneous determination of temperature fields in gaseous flows based on planar laser-induced fluorescence by integrating structured illumination with the two-line thermometry technique using nitric oxide as a tracer. This approach allows the capture of two fluorescence images originating from the simultaneous probe of two rotational states of nitric oxide (X2Π, v” = 0) using one detector and their subsequent deconvolution using spatial frequency analysis. Average experimental temperature measurements in an underexpanded jet demonstrate the viability of this approach, suggesting that the laser spatial modulation frequency and laser orientation with respect to the flow field under study impose the achievable spatial resolution limits.