An experimental study of a transversely forced round jet
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It has been well established that an interaction between combustion and acoustics can produce self-sustained acoustic oscillations. In recent years, thermo-acoustic instabilities have been a hot research topic, mainly because of a drive for more environmentally friendly gas turbines. Reducing NOx and CO gas emissions and increasing efficiency means lean combustion, but this makes the combustion chamber of the gas turbine more prone to self-induced thermo-acoustic instabilities. These thermo-acoustic instabilities are not fully understood, and are detrimental to both the efficiency and structural integrity of a gas turbine.In an effort to shed some light on the matter, this thesis studies a jet experiencingtransverse acoustic forcing. It deals with a non-combusting (air) jet forced with speakers,in order to remove the additional complications of thermal interactions, and gain a better grasp of the fundamental mechanics behind.An acoustic chamber was constructed which could be set up in multiple configurations.A total of 6 configurations were tested for suitability for experiments. A number of simulations were carried out in order to predict the responsesExtensive acoustic characterisations of each configuration was carried out and evaluated. These involved mainly frequency sweeps, where the acoustic response of the chamber was tested over a range of frequencies, and mode evaluation, where data gathered on the amplitudes of microphone signals was compared to prediction from simulations.The best configuration was selected, and the effect of transverse acoustic forcingon an air jet was investigated. Significant PIV images were not obtained within the time constraints, and thus the final discussion revolves around the raw images themselves rather than PIV images.Seven positions ranging inbetween the pressure antinode and node of the acoustic field were filmed. Finally, the images showing hitherto unobserved vortex rollups were discussed.