At Vanderbilt, we both develop and apply laser diagnostic techniques for combusting flows. Laser-based techniques are preferred because of the non-intrusive nature of the measurement. This important attribute helps insure that the act of measuring the flow does not change its behavior. Most alternative methods (e.g. gas chromatography or thermocouples) do not share this feature, and require insertion of a probe into the measurement zone. This can radically change the field (e.g. the formation of shocks in supersonic conditions) or simply pose material issues with probe (due to the extreme heat of particular flows).
The two main techniques we currently utilize measure different types of quantities: velocity/vorticity measurements, and multi-species/temperature measurements. Velocimetery techniques are usually used to measure over a 2D planar cross-section of the flow-field of interest. The technique most often used is termed Molecular Tagging Velocimetery (MTV), where the molecules are "marked" and "read" to measure time-of-flight and deduce flow-field characteristics. Two methods currently employed use the tracers OH (using water as the source) and NO (from N2O).
Chemical composition measurements are most often conducted using Spontaneous Raman Scattering (SRS), which allows the simultaneous measurement of temperature and major species concentrations using a single laser light source. This technique provides a 1D spatial measurement; however, has been expanded to measure 2D cross-sections of steady flows.
We apply the techniques to various flow-fields, both reacting and non-reacting, to further advance the field. To learn more, use the links to the right.