Abstract
For the case of quasi-periodic flow, it is demonstrated that use of the hydrogen bubble timeline method leads to reasonable estimates of the eigenfunction of the streamwise velocity fluctuation. Both amplitude and phase distributions across an unstable wake flow are well-approximated. It is shown that the vorticity extrema, as well as the degree of concentration of vorticity, are in good agreement with those calculated from linear stability theory. A critical assessment is given of the possible uncertainties associated with this technique: the existence of a finite, but unknown cross-stream velocity component; bubble rise due to buoyancy effects; wake defect created downstream of the bubble wire; and resolution of the digitized image. Furthermore, the uncertainty in the streamwise velocity, arising from existence of a finite cross-stream velocity component, is actually less than that corresponding to a single-element hot film probe over certain regimes of operation.
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Lusseyran, D., Rockwell, D. Estimation of velocity eigenfunction and vorticity distributions from the timeline visualization technique. Experiments in Fluids 6, 228–236 (1988). https://doi.org/10.1007/BF00187362
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DOI: https://doi.org/10.1007/BF00187362