Investigation of coherent structures in a triple jet by Raman scattering

An optical method is developed that allows the investigation of coherent structures in multicomponent gas flows. The method is tested on the flow field of a triple jet with different initial conditions. Linear Raman scattering is applied for concentration measurements. The autocorrelation function of the Raman signal is recorded. In addition, the frequency of occurence of the amplitudes of the Raman signal is measured. The analysis of correlation measurement of the Raman signal together with the measurement of the amplitude distribution allows recovery of the regular periodic structure of the concentration variations caused by vortex rolls that are moving through the observation volume. Flow visualization by laser-induced iodine flourescence gives an additional picture of the flow structure.