The impact of flame stabilisation and coherent flow structures on the noise emission of turbulent swirl flames

摘要

The development of modern jet engine and stationary gas turbine applications is focused on the reduction of pollutants and, increasingly, on the reduction of noise emissions including combustion noise. This requires the minimization of noise sources, namely noise from the turbulent flow, combustion noise and noise caused by periodic flow and combustion instabilities or fluctuations of the ignition zone. This has to be achieved under conservation of the benefits of swirl flames, i.e. high ignition stability and broad operation ranges. The presented experimental work enables to relate the total noise generation of swirl flames to its physical sources: turbulent flow noise, combustion noise, noise caused by a lifted, unstable flame stabilization and the combustion of coherent flow structures, the latter being caused by the burners exit geometry [1, 2]. Different positions of the flame stabilization can cause an increase of combustion noise up to 3 dB. With the results it is possible to prevent additional noise to the unavoidable minimal combustion noise, evoked by stochastic, turbulent fluctuations of the mixture density, i.e. optimization of the ignition stability with a perfectly premixed pilot flame. Further insight was gained about the influence of the gas injection direction on the combustion noise, where some configurations lead to an increase up to 6 dB in comparison to the results of premixed flames [2], which in general are louder than all investigated non-premixed flames.