PUB - Publikationen an der Universität Bielefeld

A new approach for the measurement of turbulence time scales was developed based on double-pulse two-dimensional laser-induced fluorescence in combination with a correlation analysis. In a first application, the reaction zone of a turbulent H-2/air diffusion flame was studied with this method. For this, OH molecules were excited using two laser pulses which were delayed with respect to each other, but which pumped the same transition in the OH A-X (1,0) band. The laser-induced fluorescence of the same spatial region was detected using two gated CCD cameras. By varying the time delay between the laser pulses from 5 mus to 1 ms, the temporal changes of the OH-containing structures were determined. Spatial structures were also examined. Correlation analysis was used for a quantitative evaluation of the experimentally observed time and length scales for the regions where OH was present. The double-pulse 2D LIF method appears to be a promising tool for the investigation of turbulent flows. Its applicability is not limited to the example presented here. With the possibility to detect stable as well as radical species, it may provide a wealth of data on the temporal and spatial changes of a variety of scalars in both non-reacting and reacting turbulent flows which can be compared to mathematical turbulence models.