Time-domain measurements in separated flows

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Abstract
This paper describes a sampling technique which is non-periodic, but also non-random, and which allows a pulsed wire anemometer to be used to obtain time-domain information in separated flows. Data free from aliasing can be obtained at frequencies considerably higher than that associated with the maximum possible (periodic) sampling rate achievable with a pulsed-wire probe. Autocorrelation and spectral data obtained in three quite distinct types of flow are presented, as a demonstration of the technique. Some of the data serve to emphasize the special character of separated flows. It is shown that in some circumstances it is possible to obtain spectral data that are adequate for estimating the turbulent-energy dissipation rate (provided that an inertial subrange exists). The measurement of all the terms necessary to examine the balance of turbulent energy in separated flows – or, at least, those terms which can be obtained by standard hot-wire anemometry in low-intensity flows – is therefore a distinct possibility.