Filtered Rayleigh scattering velocimetry—accuracy investigation in a M=2.2 axisymmetric jet

The present study is a quantitative evaluation of filtered Rayleigh scattering (FRS) axial velocity measurements in a M=2.2 axisymmetric jet. The FRS setup used a frequency-doubled, injection-seeded Nd:YAG laser, an iodine vapor cell and two intensified CCD cameras. The goal was to evaluate the FRS accuracy in a practical flow case and assess the relative uncertainty contributions of different sources. Despite the use of dried air and co-flow, water condensation produced uneven seeding of the flow, making particle scattering dominate over molecular scattering. The time-averaged velocity measurements showed fair agreement between the FRS and pressure probe data acquired in the same setup with deviations of up to 50 m/s. The analysis of uncertainty sources showed that laser drift dominated with an estimated contribution of 35 m/s. Several other sources, shot noise, iodine cell calibration, image misalignment and non-monochromatic scattered light were found to contribute O(10 m/s) each, bringing the total uncertainty estimate to ±50 m/s, in agreement with the experimental data.