Investigation of Rectangular Jet Issuing From a Varying Cross-Section Nozzle

Abstract

A Large Eddy Simulation based investigation is performed on a rectangular Mach 0.226 jet to examine the effect of differential entrainment along the minor and major axes. The nozzle has a circular cross-section at the inlet and a 2:1 aspect ratio rectangular cross-section (5.3848cm equivalent hydraulic diameter) at the exit. The Reynolds number of the flow is 73,242. The streamwise distribution of both mean and rms axial velocity fluctuations along the jet centerline agree with available experimental data. Q-criterion iso-levels confirm the existence of large hairpin like vortices, which initially are dominant along the major axis but further downstream, appear along the minor axis as well. The integral scales of these structures are investigated through their pressure footprints along the minor axis, major axis and corner. To highlight the influence of different frequency ranges, the velocity field at the core collapse location is first decomposed using Empirical Mode Decomposition (EMD). The spectrum in these different ranges is then correlated with observations along representative lip-line at the major and minor axes and the corner. The presence of the large scale structures corresponding to low frequency ranges is predominant along the corner compared to major and minor axes. The correlations provide information on the connections between the structures and local times scales. The major components of low frequency structures in the propagated signal occur between St = 0.05 and St = 0.3