Jun 04, 2018 - The paper describes a peculiar family of eigenmodes that arise in transsonic jets (predicted for 0.82 < Ma < 1). These modes are principally composed of downstream- and upstream-propagating acoustic waves within the jet column. It is suggested, in a companion paper (Towne, Ca...

May 23, 2018 - The linear response of subsonic and supersonic jets to volume forcing is computed, with a focus on noise generation. It is concluded that sub-optimal singular modes of the resolvent are important acoustic contributors in subsonic cases. The principal acoustic beam results from the ...

May 11, 2018 - This study presents global eigenmode spectra for incompressible and subsonic jets, as well as optimal perturbations for transient temporal growth, similar to the supersonic case of Nichols & Lele (2011), but with a critical regard. The article questions the usefulness of tempor...

May 10, 2018 - Wavepacket structures in two turbulent jets at Ma=1.5 and Re=O(100 000) are extracted from LES data and compared to instability wave model predictions obtained from PSE. The strategy is similar to the subsonic jet study by Gudmundsson & Colonius (2011), which used an experiment...

May 10, 2018 - The DNS by J. Freund of a Ma=0.9, Re=3600 turbulent jet provided a detailed database of near-field instability dynamics and far-field acoustics. In this article, Freund extracts acoustic Lighthill source terms. Once the non-radiating (subsonic) Fourier components of these source di...

May 09, 2018 - This fine review article discusses the presence of wavepackets in turbulent jets. Wavepackets denote vortical structures with a much higher temporal and spatial coherence than that of the turbulent scales. They are conceptually connected to linear instability waves developing in th...

May 09, 2018 - Nichols & Lele present the first truly global linear eigenmode calculations for jets. The paper is short, in the JFM fast track format, and therefore focuses on one single configuration, at Mach number 2.5 and Reynolds number 3600. Similar results for other Mach numbers (>=0...

May 09, 2018 - An extensive comparison between experimental measurements in a high-Re turbulent jet and linear instability predictions is made in this paper. The idea is very similar to that of Gudmundsson & Colonius (2011), but the new experimental database allows a frequency-resolved repres...

May 04, 2018 - This paper demonstrates the presence of coherent wavepacket structures in the near-nozzle region of a turbulent jet, measured in the form of multi-point correlations in the acoustic near field. These wavepackets are shown to behave as linear spatial instability waves in the turbule...

May 04, 2018 - This paper demonstrates that the self-sustained oscillations in hot jets are caused by the underlying absolute instability (for the latter, see Monkewitz & Sohn 1988 and Lesshafft & Huerre 2007). The same has of course been inferred already by Sreenivasan et al. 1989 and by...

May 07, 2018 - Two main questions are treated in this article: What physical mechanism causes absolute instability in low-density jets? How are shear-layer and jet-column instability modes properly characterised and distinguished? The analysis is local, and entirely based on spatio-temporal mod...

May 04, 2018 - Jendoubi & Strykowski investigate the "spatio-temporal" instability of parallel jet profiles. Technically, they compute the absolute mode for velocity profiles with varying counterflow. Physically, these modes represent perturbations with non-zero group velocity in a ...

May 04, 2018 - Following the discovery of absolute instability in hot jets, this experimental study confirmed the onset of self-sustained oscillations in hot jets, as the temperature ratio (or equivalently, the density ratio) falls below a critical value. Two distinct self-sustained states were f...

May 04, 2018 - This conference paper, which was never made into a journal publication, established the occurrence of absolute instability in jets that are significantly heated with respect to the ambient fluid. The effects of Mach number, density ratio and shear layer thickness (via a profile par...

May 04, 2018 - I choose this article as a starting point for the historical timeline, as it gives a comprehensive summary of Michalke's results on jet instability from the 70s and early 80s, and it is still widely cited today. All results in this paper are obtained from spatial instability analys...