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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Computational aeroacoustics study of circular and elliptical jets

Author: ALONSO, Mikel

Year: 2007

Supervisor(s): Eldad Avital

The sound generated by single and coaxial circular and elliptic jets was studied computationally. An indirect Computational Aeroacoustics (CAA) approach was used where the hydrodynamic field was calculated by an incompressible Large-Eddy Simulation (LES) method and the sound field was calculated using Lighthill’s acoustic analogy. This study is divided into three parts. In the first part the hydrodynamic results for low Reynolds number jets are presented. The effect of variation in the inflow momentum thickness was also investigated. The circular jet was found to be dominated by larger structures that the elliptic jet. The elliptic jet showed enhanced mixing and axis-switching. As a result the elliptic jet’s end of the potential core occurred further upstream than in the circular case.

The second part contains a study of the basic sound radiation of low Reynolds number jets using Lighthill’s formulation of the acoustic analogy. The acoustic power spectrum and the individual quadrupole spectrum showed a slight decrease in acoustic emission in the elliptic case. The location of the acoustic source revealed that the elliptic jet’s dominant emission occurred upstream of the circular jet’s. The sound directivity showed that the dominant radiation direction was in the longitudinal direction. Adding a secondary jet did not necessarily reduce the sound emission; varying the inner to outer velocity ratio was found to have an important effect.

The third part contained the results for moderate Reynolds number simulations. The reduction in molecular viscosity incurred enhanced mixing and an increase in sound emission in all directions. The proposed boundary correction for Powell’s formulation provided a very good agreement with Lighthill’s formulation prediction.