PIV measurements of subsonic installed jets

Resumo

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.In this paper we perform stereo particle image velocimetry (stereo PIV) of subsonic installed jets. A flat plate was used to mimic a jet/wing/flap interaction and velocity field measurements were performed for jet/plate configurations known to produce different acoustic spectra: broadband, linear frequency selection (LFS) tones and strong oscillator spectra associated with non-linear frequency selection (NLFS). The velocity field was measured at several cross-stream planes from the nozzle exit up to 15 jet diameters downstream. The measurements show that up to the plate trailing-edge, the flow field is close to axisymmetric, whereas downstream of the plate, for small jet-edge separation, the jet is strongly deformed. Spectral proper orthogonal decomposition (SPOD) was employed to identify coherent structures in the data. The database was treated with and without D1-dihedral group decomposition. SPOD spectra exhibit features similar to those of the associated acoustic spectra, especially when tonal peaks are present. The SPOD spectra are consistent with the resonance mechanism proposed by Jordan et al. (J. Fluid Mech., vol 853, 2018, pp. 333-358). Low-rank behavior is observed upstream of the trailing-edge for the LFS and NLFS scenarios. The leading SPOD modes in the tonal cases show features consistent with the k+, and k- waves that underpin resonance in the model of Jordan et al.