The non-linear parabolized stability equations (NLPSE) are implemented in a hybrid model for studying noise from round jets. The NLPSE computes instability waves in the flow that may interact nonlinearly to produce noise. This mechanism for noise generation is believed to be a significant contributor to low-frequency noise from subsonic round jets. The NLPSE code has been validated against direct numerical simulation (DNS) data for a number of model problems and the suitability of the method for modelling jet flows has been studied by comparing the results with D S. Near-field results show good qualitative agreement with the DNS. However, the LPSE over predicts the magnitude of near-field fluctuations, which degrades the quality of the final sound-field prediction. It is found that the NLPSE results are highly dependent on the rate of divergence (non-parallelism) of the mean-flow and that a certain amount of eo-flow is necessary to stabilise the downstream-marching numerical scheme for solving the NLPSE. Changing the Mach number confirmed that the NLPSE is very well suited for supersonic jet studies but has difficulty resolving low Mach number jets. It is found that hot jets are also numerically difficult to resolve because the magnitudes of the instability waves increase greatly as the temperature is increased. A linearised Euler equation (LEE) code has been adapted to the round jet problem and found to be an accurate tool for obtaining the sound field from sources defined in the near-field of the jet. By including sources into this code, a LPSE-LEE hybrid code has been implemented, with the LEE part validated against DNS by using modelled near-field sources. Use of this new approach has shown that much can be learnt about the behaviour of jets and the parameters that influence the noise they produce.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:560810 |
| Date | January 2012 |
| Creators | Salgado, Adriana M. |
| Publisher | University of Southampton |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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