| Autor: |
Bassetti, Alessandro |
| Rok vydání: |
2009 |
| Předmět: |
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| Druh dokumentu: |
Electronic Thesis or Dissertation |
| Popis: |
We introduce a hybrid model for the evaluation of jet noise. The model uses the information from a solution of the Reynolds-averaged Navier{Stokes equations (RANS). It evaluates the jet-noise power spectral density (PSD) in the quiescent region outside the turbulent jet. It includes the following components: 1. A propagation model based on the high- and low-frequency approximations of the Lilleyanalogy Green's function. The high-frequency approximation is determined by combining a moving-medium Lighthill analogy and ray acoustics. The low-frequency model is made by using a ow-factor approach on each component of the source two-point CPSD. We use available analytical expressions of ow factors evaluated in the low-frequency limit. 2. A xed-frame source model based on the source terms of the Goldstein (2001) expression for the Lilley analogy. Both the applied-stress and applied-force equivalent acoustic sources are retained. The used acoustic analogy allows for expressing the 2-point covariance of the applied-stress source by using 2-point velocimetry measurements in a turbulent jet. Specically the applied-stress source can be put in correspondence to the unit-density Reynolds-stress statistics. Available measurements of the unit-density Reynolds-stress 2-point statistics are here used to derive an analytical model for the applied-stress 2-point correlation coecient. Also the applied-force 2-point statistics, required for modelling noise source mechanisms at the presence of density inhomogeneities in the ow, is expressed on the basis of the unit-density Reynolds-stress 2-point statistics. Numerical methods are used to derive the frequency{wavenumber expression for a volumetric source-strength tensor. 3. A jet- ow prediction by using a commercial RANS solver and a set of connection relations expressing source-model parameters starting from the RANS solution. The RANS system includes Reynolds Stress modelling (RSM) closure equations. Turbulence anisotropy is then incorporated in the ow-statistics estimation. The proposed connection relations introduce a set of empirical parameters which are evaluated by matching model components to both velocimetry and acoustics measurements. Modelled far-eld jet-noise 1/3-octave spectra are compared to corresponding measurements for isothermal, unheated and hot jets. |
| Databáze: |
Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
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