Abstract
A real-time digital imaging technique has been applied to smoke flow visualized turbulent flows to provide statistical data concerning bluff body wakes. The 'digital imaging technique' has been successfully applied to the wake of a two-dimensional flat plate, circular cylinder and a jet in a crossflow configuration. A detailed study of the two-dimensional flat plate model involved comparative hot-wire and pressure measurements combined with data from previously published experimental investigations. The results obtained included, intermittency measurements, vortex shedding spectral analyses (autocorrelations), spatial correlations, wake interface statistics and turbulence data. In the majority of cases, the digital imaging technique was found to provide excellent quantitative detail whilst also offering some unique wake interface statistics. The experiments conducted on the circular cylinder model revealed details of secondary vortex shedding and their base-bleed dependence, whilst the jet in a crossflow configuration enabled the imaging technique to be applied to a complex, three-dimensional flow model. The resulting iso-intermittency contour map was produced expediently, and within an experimental period far shorter than could be expected for single-location probe measurements. In addition to the above-outlined quantitative technique, real-time digital imaging was also applied more qualitatively to the study of dynamic stall on an aerofoil and to the enhancement of high-speed vapour-screen visualizations, both techniques offering the possibility for enhanced quantitative flow studies in future investigations. Finally, true-colour video digitisation has been exploited in a preliminary study of the quantification of global surface shear stress values using liquid crystal technology. Although in its infancy, the realisation of an experimental procedure along such lines would be of immense benefit to experimental aerodynamic research.