“Fluid-Thermodynamic Mode Decomposition of a Supersonic Jet”
The flowfield of a Mach 1.3 cold jet obtained through Large-eddy Simulation is decomposed into its acoustic, hydrodynamic and thermal components using Doaks’s momentum potential theory. The hydrodynamic mode closely follows the shear layer roll-up and core turbulence. Both acoustic and thermal modes reveal themselves as having wavepacket form in the core region. The acoustic mode reproduces the universal spectra observed in the sideline and downstream directions. The filtering properties of the jet along the shallow-angle direction are examined using scalograms. Although broadband in the core, the hydrodynamic mode has peak energy around St = 0.08 in the nearfield. On the other hand, the acoustic mode has a narrowband nature around St = 0.2, with distinct intermittent events in the nearfield. The acoustic coherent axial wavepacket has a principal frequency of about St = 0.4 and exhibits jittering phenomena, yielding the nearfield radiation pattern. An analysis of the total fluctuating enthalpy (TFE) transport equation highlights the role of individual modes in the generation and transport of acoustic energy to the nearfield of the jet. While the solenoidal fluctuations contribute the most to sideline radiation, the downstream transport of acoustic energy occurs primarily through the irrotational field. For this cold jet, the hydrodynamic mode is found to be the primary source of radiated energy due to its interaction with the fluctuating Coriolis acceleration. The entropic fluctuations lead to dissipation of the Total Fluctuating Enthalpy.
22nd AIAA/CEAS Aeroacoustics Conference