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Frequency scanning filtered Rayleigh scattering is able to simultaneously provide time-averaged measurements of pressure, temperature and velocity in gaseous flows. By extending the underlying mathematical model, a robust alternative to existing approaches is introduced. Present and proposed model functions are then characterized during a detailed uncertainty analysis. Deviations between the analytical solution of a jet flow experiment and measured results could be related to laser-induced background radiation as well as the Rayleigh scattering’s spectral distribution. In applying a background correction method and by replacing the standard lineshape model by an empirical formulation, detrimental effects on pressure, temperature and velocity accuracies could be reduced below 15 hPa, 2.5 K and 2.7 m s−1.

The filtered Rayleigh scattering (FRS) technique, extended by the method of frequency scanning, is a powerful tool to characterize thermodynamic, as well as aerodynamic, properties of technical flows. In this Letter, we report on the first application of an FRS velocimeter, which is capable of acquiring time-averaged planar pressure, temperature, and three-component velocity distributions simultaneously. The method is validated by characterizing the near-field, as well as the far-field, of a turbulent jet.

This paper shows the importance of considering the thermal state of a combustor to investigate or predict its thermoacoustic stability. This aspect is often neglected or regarded as less important than the effect of the operating parameters, such as thermal power or equivalence ratio, but under certain circumstances it can have a dramatic influence on the development of the instabilities. The paper presents experimental results collected from a combustor featuring a lean swirl-stabilized flame exhibiting thermoacoustic instability at some operating conditions. It is shown that this instability is caused by a change of the flame topology that is induced by the progressive increase of the wall temperature with the thermal power. This dependence of the instability on wall temperature leads to inertial effects and hysteresis when the operating condition is changed dynamically. A low-order model of the system reproducing this remarkable dynamics is proposed and validated against the experimental data.