The present observations showed that over the large source domain considered around a mixing layer, the acoustic pressure signal has not its source at a specific flow event or stress field in the vortex-pairing region, but is rather determined by the vicinity of the observer. Is that way of thinking a fancy of the mind ? There are some intrinsic limitations of the present analysis: firstly, the observer is inside the source region, thus the analogy assumption of the source - observer separation is violated; but this separation is between the phenomena: the flow excites the wave equation as an externally applied source term.
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