Abstract
Ultra high-speed image sampling is integrated with rainbow schlieren deflectometry (RSD) to obtain spacetime cross-correlation measurements in a turbulent helium jet of diameter, d = 4 mm and Reynolds number of 4000. Rainbow schlieren apparatus was configured to cover the near field axial range of 0 to 20 diameters downstream of the injector exit at pixel resolution of 124 μm, image acquisition rate of 50,000 frames per second, and image exposure time of 20 μs to capture wide range of turbulent structures. Spacetime cross-correlations of deflectometric data yield mean convection velocity profile, axial and transverse wavenumber spectra, temporal spectrum, spectral coherence, and integral length and time scales. Such information is useful from experimental validation of large eddy simulation (LES) and a step towards creating data base for LES validation is undertaken in this study. Ultra high-speed imaging integrated with RSD can provide statistics characterization of turbulence through scalar measurements to compliment velocity field information obtained by other measurement technqiues.
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