Combustion Noise and Dynamics of partially premixed flames

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Combustion Noise and in particular combustion instability are two significant problems for the development of reliable, low emission jet engines. Compared to other types of aeronautical noise, the relative importance of combustion noise has increased in the last decades. Thermoacoustic combustion instability is a design challenge that must be confronted as aero engine combustion moves towards lean operating conditions in order to satisfy emission regulations on oxides of nitrogen. Consequently, the development of modeling concepts and simulation tools to investigate and control these two phenomena - which are closely related to each other on a fundamental level - becomes mandatory for the design of engines that are clean, quiet, stable and capable of working over a wide range of operating conditions.A joint ANR/DFG project "NoiseDYN'" between Centrale Supelec in Paris and TU München developed and validated tools for the simulation and identification of the dynamics of confined turbulent premixed flames as well as the corresponding sources of direct combustion noise. In continuation of these efforts, the proposed project “NoiSI” will contribute to the development of a general, unified framework to model combustion noise and thermoacoustic instability in aeronautical gas turbines.This framework relies on data-based, reduced order models of flame dynamics and combustion noise. It comprises three steps: i) perform high-fidelity numerical simulation of confined, turbulent, partially premixed flames, ii) evaluate the flame dynamics and the sources of direct as well as indirect combustion noise by means of advanced system identification, and iii) integrate individual elements (sources and flame responses) in a low-order acoustic network model for the assessment of combustion noise levels and instability margins. The main objectives of the NoiSI project are the following: First, to establish and validate a framework to evaluate the response of flames to acoustic and fuel concentration perturbations and the corresponding sources of combustion noise and entropy waves. The approach envisaged relies on high-fidelity numerical simulation (LES), advanced system identification (SI) and uncertainty quantification and is conceived to remain computationally affordable also for configurations of applied interest. Second, establish a thermoacoustic network model that takes into account all physical mechanisms relevant for combustion noise and instability of turbulent flames by incorporating the sources and flame responses evaluated previously with LES/SI. A high-pressure, liquid fuel combustion test rig (SCARLET rig at DLR Köln) and a lab-scale, gaseous fuel combustor at ETH Zürich will be investigated. The numerical simulations and modeling strategies proposed will be validated against experimental results.