PhD Defense - C. Silva

Numerical study of combustion noise in gas turbines

Delivered by University of Montpellier II
Speciality: Mathematics

November 9, 2010 - CERFACS

Today, much of the current effort in combustion noise is the development of efficient numerical tools to calculate the noise radiated by flames. Although unsteady CFD methods such as LES or DNS can directly provide the acoustic field radiated by noise sources, this evaluation is limited to small domains due to high computational costs. Hybrid methods have been developed to overcome this limitation. In these schemes, the noise sources are decoupled from the radiated sound. The sources are still calculated by DNS or LES solvers whereas the radiated sound is evaluated by acoustic tools using an acoustic analogy.
In the present study, a numerical tool based on the Phillips analogy for low Mach number flows has been developed. This tool accounts for the role of the boundary conditions in the resulting acoustic field. Both LES and the acoustic solver developed here are used to assess the noise produced by a turbulent swirl-stabilized flame generated in a staged combustor. Good agreement is obtained between both techniques as long as the appropriate quantities are compared: the pressure signal obtained directly from LES contains a non negligible amount of hydrodynamic fluctuations that must be removed when a suitable comparison is sought with the acoustic solver.
The low Mach number assumption is completely realistic when considering the flow within a combustion chamber; it also allows for considerable simplifications when dealing with acoustic analogies. However, it cannot be used for the upstream (air-intake, compressors) and downstream (turbines, nozzle) sections of an aeronautical combustion chamber. A numerical tool is developed based on the quasi-1D Linearized Euler Equations in order to account for convective, non-isentropic and non-isenthalpic flows. By means of this tool, it is possible to estimate the acoustic boundary conditions that should be imposed at the inlet/outlet of a given combustion chamber when performing low-Mach number acoustic computations.

W. Polifke	Professor - Technische Universität München, Germany	Referee
U. Schröder	Professor - RWTH Aachen, Germany	Referee
A. Morgans	Professor - Imperial College, London	Member
B. Mohammadi	Professor - CERFACS, Toulouse	Member
S. Moreau	Researcher - University of Sherbrooke, Canada	Member
T. Schueller	Researcher - EM2C, Ecole Centrale Paris	Member
F. Nicoud	Professor - University of Montpellier II	Advisor