Acoustic Resonances in Ducted Jet Systems

The results of selected test cases are presented and the main features of resonant and non-resonant regimes for this model problem are discussed. A high-amplitude resonance, qualitatively similar to experiments in more complex geometries, was observed for a symmetric overexpanded M jet 1.2. It is seen that the resonance depends upon acoustic fluctuations reaching the nozzle lip and exciting the shear layers of the jet, the growth of the shear layer perturbations until vortices are rolled up and convected downstream, the interaction of the vortices with the shock-cell structure releasing another pressure pulse from the jet, and the reflection of this pulse in the duct walls closing the cycle. Results for a ducted non-resonant jet at Mjet = 1.5, and for a free jet at Mjet = 1.2 are also presented, to provide for comparisons with the resonant jet. The hydrodynamic mechanism is studied using linear stability analysis of the jet, where good qualitative agreement with the data from the DNS is obtained, especially near the inflow. For the acoustic part, the Fourier analysis of the data reveals the presence of excited normal modes of the duct. The hydrodynamic perturbation pattern near the inflow is consistent with the excited modes present in the duct. Furthermore, a numerical experiment is carried out where the normal mode of the duct of highest amplitude is damped, with the result that the resonance behavior is suppressed after a few cycles. The implications of the results obtained in the model problem on the resonance phenomena in test tell facilities are also discussed.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Theoretical and Applied Mechanics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Topalian, Victor D.

Contributors dc:contributor

• Jonathan Freund

• Engineering, Aerospace

Language dc:language

eng

Identifier

(MiAaPQ)AAI3363100

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/87756