Abstract The object of this paper is to present some experimental results relating to the part of the jet where a potential core exists. The measurements have been made, in the main, in the nonturbulent regions of the jet (viz. the potential core and the entrainment region), and they suggest that underlying the normally-accepted picture of a random process in the mixing region of the jet there exists a relatively periodic and deterministic flow structure. A simple model of jet structure, purporting to explain the particular phase relationships between the fluctuating pressure and the components of the fluctuating velocity obtained here, is postulated. This model appears to be well substantiated and found to be applicable even to conditions in the mixing region, provided allowance is made for non-linear effects to take place in the mixing region. A special study was made of the use of standard microphones for measuring pressure fluctuations in regions of significant mean flow, and it was found that, to a first-order approximation, this method was justified.
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