Indirect Combustion Noise Contributions in a Gas Turbine Model Combustor with a Choked Nozzle

Direct and indirect combustion noise sources co-exist in combustors. Direct noise results from unsteady combustion. Indirect contributions are associated to entropy fluctuations convected through flow accelerating devices, such as a nozzle. Many analytical and numerical studies on combustion noises have been achieved since the late 1970s yet few experimental studies were carried out to discriminate direct from indirect contributions. An experimental method to compute direct and indirect nozzle transfer functions separately has been developed in our previous work (Tao et al., 2013). It consists of measuring the direct and indirect noise transfer functions through simultaneous pressure and temperature fluctuation measurements. The method has already been validated in a well-controlled test bench, which generates temperature and acoustic fluctuations without the complexity of combustion. This article discusses the application of the methodology in a pressurized burner based on simulations of acoustic and entropy fluctuations in the combustion chamber.