Indirect Combustion Noise Generation in Gas Turbines

The paper investigates the indirect combustion noise, which is generated during the acceleration of the convected entropy nonuniformities of the combustion products in the outlet nozzle of the combustion chamber. The generation mechanism of the indirect noise is proven experimentally and through numerical simulation. Probe microphones and fast thermocouple probes were used to measure pressure and temperature uctuations. The generation of indirect noise is veried via the phase relationship between thermocouple and microphone signals. The o w eld in the combustion chamber is simulated by means of an unsteady RANS computation. Self excited oscillations are used for the computation of the direct and indirect noise generation of the combustion chamber. Since the related frequencies are low and the corresponding scales much larger than the turbulent scales, a CAA-method is employed for both the propagation of sound waves as well as entropy perturbations. It is shown that the CAA method is capable to describe the acoustical properties of the combustion system found in the experiments when the URANS simulation is used as input. The experimental results also show that indirect combustion noise may contain high frequency noise contributions, which are generally attributed to turbine noise.

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