Wavelet-based algorithm for correction of beam-steering artefacts in turbulent flow imaging at elevated pressures

Advanced Turbulent Combustion Physics and Applications

“…The remaining stripes are generated by the turbulent mixing field of helium and methane, which have disparate indices of refraction. Figure 2.20b2 shows the same Rayleigh scattering image that has been corrected using a waveletbased filtering algorithm [273]. A comparison of the zoomed-in plots of the corrected and uncorrected images shows that this method is very effective at removing the stripe artefacts while preserving the turbulent mixing data.…”

“…The effects of beam-steering artefacts are highlighted by an example of mixture fraction measurements using Rayleigh scattering imaging in a high-pressure transient gas jet [273]. Figure 2.20a shows the experimental configuration for high-speed Rayleigh scattering imaging measurements that were performed in a transient jet of helium injected into a methane bath gas at approximately 8 bar in the pressure vessel.…”

“…The image sequence is a subset of the 500 shots that were recorded during a 5 ms duration burst from the laser. The wavelet method takes advantage of the coherence length scale of the beam-steering artefacts along the direction of the beam propagation, and details of this wavelet-based filtering approach can be found in [273]. This approach enables more quantitative imaging measurements of highpressure turbulent flows at elevated pressures and other flows with large index-of-refraction variations.…”