Sound Generation in the Outlet Section of Gas Turbine Combustion Chambers

Abstract

Indirect combustion noise is investigated experimentally and numerically. This noise is generated in the outlet nozzle of combustion chambers if the entropy of the medium is nonuniform, which is the case in the exhaust of combustors. The contribution to the total noise emission of aeroengine combustors is not known. A test rig for the experimental investigation of this noise emission in the presence of swirl is first described. The indirect noise is generated in an exchangeable convergent-divergent nozzle at the exit of the combustor. The noise radiation is studied in a circular exhaust pipe with probe microphones using a radial mode analysis of the microphone signals. First results of the measured sound fields are reported. The experimental situation will be studied numerically with a 4 th order accurate CAA-method, which is first validated with theoretical results of the literature for the cases of a compact nozzle or diffuser and incoming entropy and sound waves in a one-dimensional mean flow. The agreement with the results of sound generation due to incoming entropy waves and the sound reflection and transmission for incoming sound waves is very good. The method is then applied to the more realistic cases of non-compact nozzles and it is found that the amplitudes of the generated waves are substantially smaller in comparison to the one-dimensional theory. The sound generation of real cases like a swirling hot-spot and entropy waves in a one-dimensional flow through a convergent-divergent nozzle as well as plain entropy waves in the swirl flow of the experimental setup are finally studied and the noise emission is computed.

CAA Simulation and Intensity Based Evaluation of a Model Experiment for Indirect Combustion Noise

“…The most simple model covering indirect combustion noise, and describing the transport of all possible modes of perturbation [2] in the wake of a flame, are the linearized Euler equations including anonisentropic energy equation supplemented by asource term to account for the instationary heat input [14],…”

“…Ap artially overlapping zonal approach based on aunsteady RANS simulation of the source zone wasfor example described by Schemel et al [14] using asponge layer to couple the perturbations from the CFD simulation into the propagation zone. An overviewonthe general procedure of applying CAA methods for the simulation of indirect combustion noise can be found in Schemel et al [14] and Richter and Thiele [15].…”

“…Ap artially overlapping zonal approach based on aunsteady RANS simulation of the source zone wasfor example described by Schemel et al [14] using asponge layer to couple the perturbations from the CFD simulation into the propagation zone. An overviewonthe general procedure of applying CAA methods for the simulation of indirect combustion noise can be found in Schemel et al [14] and Richter and Thiele [15]. The current paper concerns the stand alone application of an axisymmetric CAA method (TUBA) to as implified model experiment [16] in order to showthe requirements for such amethod and the capabilities it provides.…”

Core Noise Diagnostics of Turbofan Engine Noise Using Correlation and Coherence Functions

“…The method revealed delay times from the internal combustor sensor to the far-field microphone, even though the correlated signal contained both periodic and random components. In addition, indirect combustion noise has been investigated numerically and with model-scale experiments by Schemel et al [32], Richter et al [33], and Bake et al [34][35][36].…”

Spectral Separation of the Turbofan Engine Coherent Combustion Noise Component

“…34 measured the cross spectra between temperature and pressure in a constant area duct downstream of a combustor and showed that the entropy fluctuations (hot spots) moved with the flow speed. Schemel et al (2004) 35 studied experimentally and numerically entropy noise generated by hot spots (from a combustor) passing through a nozzle. Richter et al (2005) 36 studied the application of computational aeroacoustic methods to indirect combustion noise generated by hot spots passing through a nozzle.…”