Linear and nonlinear entropy-wave response of technically-premixed jet-flames-array and swirled flame to acoustic forcing

摘要: Abstract Broadband combustion noise is a major part of the total radiated by modern jet engines. It comprises two components: direct originating from unsteady heat release flame, and indirect resulting acceleration entropy fluctuations in turbine stages. Not only do these waves contribute to pollution aeroengines, they can also have crucial role feedback loop leading thermoacoustic instabilities, which induce vibrations thermal loads that are highly detrimental for combustors components. Thus, there critical need understand model complex mechanisms associated with generation advection waves. This study presents quantitative measurements production technically premixed turbulent combustor, subject acoustic forcing. Entropy transfer function (ETF) relating input, obtained microphones, wave output, OH-LIF thermometry at distance four flame heights burner outlet, were measured between 40 Hz 90 Hz. These ETF using burners same length technical premixing air natural gas, operated power: matrix producing an array flames, single swirled flame. found exhibits low-pass behavior, gain ranging approximately 0.7 40 Hz down 0.25 90 Hz, while was not exceeding 0.2. demonstrated nonlinear, dramatic drop occurring beyond certain level forcing amplitude. be used derive predictive nonlinear models instabilities involving feedback.