Assessment of a novel flow visualization technique using photodissociation spectroscopy

The study of complicated flows continuously calls for new nonintrusive flow diagnostics. A novel flow visualization technique based on photodissociation spectroscopy (PDS) is described, demonstrated, and assessed in this paper. This technique is centered around the creative use of photodissociation (PD). A PD precursor is seeded in the flow of interest, either passive or reactive. A laser pulse is then generated to completely and rapidly photodissociate both the precursor and the products formed from the precursor (if it reacts) into photofragments. A target photofragment is then imaged to obtain multidimensional information about the flow. An analytical methodology was developed to assess the feasibility of the PDS-based technique. This analytical method was applied to the case where molecular iodine was used as an example PD precursor, and the results were validated by experimental data. Both the analytical and experimental findings provided a promising outlook for this new technique as a practical flow visualization technique. With a properly chosen PD precursor, the PDS-based technique provides an attractive alternative for imaging several critical flow properties, including the mixture fraction and temperature field. This technique shares some key advantages with established techniques, e.g., a high spatial and temporal resolution comparable to the planar laser-induced fluorescence (PLIF) technique. Meanwhile, this technique offers several unique advantages to overcome the limitations of existing techniques, including enhancing the signal level and simplifying the interpretation of the signal.