The response of a round jet to transverse forcing
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This project was done in two parts. The first part was to investigate the behaviourof a small jet placed in five different positions between the antinode and the nodein an acoustic field. This jet was measured with a hotwire at the jet exit andtwo microphones inside the jet. The velocity amplitudes from the hotwire and thepressure amplitudes from the microphones were plotted against each other for allfive positions. This showed that the size of the pressure amplitudes inside the jetwas linear to the velocity amplitudes at the exit, and that the gradient was thesame for all positions. The strongest amplitudes were at the antinode and theweakest at the node. The different amplitudes for the five positions were comparedto the theory of an acoustic field inside a box, and compared well, indicating thatthe measurements were done correctly. The second part was a larger jet that was acoustically forced with the node placedat the centre of the jet. Eight microphones were mounted flush around the jetwith 45between them, right beneath the jet exit. The pressure inside the jet wasmeasured with these eight microphones for two different resonance frequencies.This was done to see how the steepness of the gradient affected the measurements.The results from the highest resonance frequency compared well with theory, butthe results from the lower did not. All the signals from the lowest resonancefrequency had a phase shift. This was investigated, and it concluded with that theamplitudes from the speakers were different.