Proper orthogonal decomposition analysis of the large-scale dynamics of a round turbulent jet in counterflow

Abstract

Although the mean flow features of the turbulent jet in counterflow have been studied in the past, the large-scale dynamics of this flow configuration remain unexplored. The present work presents the modal analysis, through proper orthogonal decomposition (POD), of large eddy simulations (LESs) of counterflowing jets at different jet-to-counterflow velocity ratios (α=2.2,3.4,5.1) reported in detail by Rovira, Engvall, and Duwig [Phys. Fluids 32, 045102 (2000)PHFLE61070-663110.1063/5.0003239]. In the present study, a qualitative investigation of the three-dimensional (3D) turbulent structure of this jet configuration is performed by vortex identification. Additionally, a simplified description of the origin and development of these coherent structures is presented. Planar two-dimensional (2D) POD results for the case with α=3.4 are directly compared and found to be in close agreement with the results available literature. In this case, over an equal time interval, temporal and spatial resolutions are observed to have a minor effect on mode energy content. All three cases are also analyzed with 3D POD and the evolution of the peak mode frequency with α is studied. Additionally, by employing a wavelet transform, the intermittent behavior of the fundamental mode dynamics is evidenced for the first time. Finally, the jet in counterflow case with α=5.1 is analyzed with a 3D spectral POD. Varying jet penetration, precession, and a stretching and contracting motion are found to be the most dominant modes.