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Instability wave models of turbulent jets from round and serrated nozzles


Gudmundsson, Kristjan (2010) Instability wave models of turbulent jets from round and serrated nozzles. Dissertation (Ph.D.), California Institute of Technology.


In this thesis we study pressure fluctuations associated with large-scale coherent structures in turbulent round and serrated jets. Linear disturbances to the turbulent mean flow of the round jet are modeled via linear stability analysis and the Parabolized Stability Equations (PSE). We show that PSE provides better agreement with near-field microphone-array data at low frequencies than previous models based on linear stability theory. We examine the extent to which microphone data is contaminated by fluctuations uncorrelated with large-scale structures. By filtering out the uncorrelated fluctuations, via the proper orthogonal decomposition (POD), better agreement between data and theory is obtained. We next extend the linear stability analysis of round jets to include the effects of azimuthal inhomogeneities of serrated jets. We solve the resulting system of equations and find new modes, associated with the streamwise vorticity of the serrated-jet mean flow. All unstable modes of the serrated jet are stabilized, potentially explaining the noise reduction achieved by such jets. We also compare these predictions to POD-filtered microphone measurements, generally finding good agreement.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Aeroacoustics; Jet Noise; Linear Stability Analysis; Kelvin-Helmholtz Instability; Chevron Nozzle; Parabolized Stability Equations
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Mechanical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Colonius, Timothy E.
Thesis Committee:
  • Hussain, Fazle
  • Leonard, Anthony
  • Shepherd, Joseph E.
  • Colonius, Timothy E. (chair)
Defense Date:17 November 2009
Author Email:kristjan (AT)
Record Number:CaltechTHESIS:01242010-111852941
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:5539
Deposited By: Kristjan Gudmundsson
Deposited On:31 Mar 2010 16:26
Last Modified:26 Dec 2012 03:21

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