Linear Stochastic Estimation of the Flowfield from a Bypass Ratio 8 Nozzle Configuration

Abstract

Linear Stochastic Estimation (LSE) and Proper Orthogonal Decomposition (POD) are used to compare the large-scale structures of a jet exhausted through a baseline Bypass Ratio 8 nozzle to a jet exhausted through a chevron nozzle with the same Bypass Ratio. Particle Image Velocimetry (PIV) is used to measure the streamwise and radial velocity components on a 2D streamwise plane over the first 11 jet equivalent diamters. A comparison of the mean velocity and turbulent kinetic energy (TKE) for these two cases show that the streamwise vortices generated by the chevron nozzle result in high turbulence levels near the nozzle and reduced turbulence levels downstream. The results from the LSE analysis are consistent with the TKE in that the correlations levels between the original and reconstructed flowfield are highest when the referente signals for the LSE reside at the peca in the TKE radial profiles. It was also shown that the baseline estimates from the LSE analisis could be used to reconstruct the chevron flowfield, particularly near the end of the potencial core. The POD modes further supported that the changes seen in the TKE were due to the coherent structures. The energy levels for the first few POD modes were higher for the chevron configuration near the nozzle and lower downstream. Finally, the complimentary technique was employed which combined the LSE and POD methods. The complimentary technique had lower correlation levels, but was better at reconstructing the entire flowfield compared to the LSE technique which was very localized near the peak TKE values.