AN EFFICIENT OPTICAL PRESSURE MEASUREMENT IN COMPRESSIBLE FLOWS - LASER-INDUCED IODINE FLUORESCENCE

The understanding of complex phenomena, the experimental validation of calculation codes, and the construction of data bases in fluid mechan ics require the development of non-intrusive experimental techniques, The laser-induced fluorescence of a gaseous molecule seeded into a gas how can be related to the flowfield thermodynamic parameters, such as pressure and temperature. An experimental method is described, that a llows the removal of the temperature dependence of the fluorescence si gnal. A narrow-bandwidth single-line laser is tuned to the center of a n absorption line, whose temperature dependence of the Boltzmann fract ion can be neglected. The experimental set-up requires a single-line d ye laser and a high resolution spectral analysis device. The accuracy of the method, checked in a static vessel, appears to be better than 5 %. The method has been successfully tested with a supersonic jet issui ng from an underexpanded nozzle. The experimental results have been co mpared to those of an Euler calculation. A mean difference of 14% has been observed, but a major part of this can be attributed to the diffe rence between inviscid and real gas calculation.