Examples of the Use of the Pulsed Wire Anemometer in Highly Turbulent Flow

Summary

This paper describes further applications of the pulsed wire anemometer to velocity measurements in highly turbulent flows. The measurements were all made in the near wake of the flow downstream of a normal flat plate. The near wake is characterised by a reverse flow region in which the velocity fluctuations contain both a random component and also a near periodic contribution arising from the rolling up of the vortex sheets shed from the sharp edges of the plate. Previous measurements of normal turbulent stresses by Bradbury (1976) are extended to include shear stress measurements using an inclined pulsed wire probe. Although it is not possible, at this stage, to establish the precise accuracy of these measurements, the internal consistency of the results is satisfactory and suggests that worthwhile studies involving shear stress measurements can be carried out using inclined pulsed wire anemometers.

Examples of the use of the pulsed wire anemometer in conditional sampling experiments are also described. Signals from a hot wire anemometer placed outside the wake of the flat plate were used to trigger the pulsed wire at a fixed phase in the vortex shedding cycle. The results show clearly that the complete development of the vortex shedding process in the near wake region could be studied using this technique.

Finally, the problems of obtaining spectral information from a pulsed wire anemometer are discussed. Experiments using random sampling and a sequential sampling technique are briefly described. A difficulty with both techniques is that autocorrelation estimates cannot be obtained for time lags less than about 10 milliseconds and an application of the autocorrelation function theorem to estimate these unknown autocorrelation values is described. This theorem is used in the development of maximum entropy power spectral analysis but its application here represents a new area of application of the theorem.