Droplets size characterization for cold water clouds by means of Generalised Scattering Imaging

Abstract

Abstract This paper describes an experimental investigation carried out at the Italian Aerospace Research Centre (CIRA) laboratory for the application of the Generalized Scattering Imaging (GSI) technique. The droplets were generated by a monodisperse droplet generator and a multi-disperse conical nozzle. This latter is currently used for making the artificial cloud in the CIRA Icing Wind Tunnel (IWT). The measurements are devoted to assessing the application of GSI for the characterization of the cold cloud of CIRA-IWT. The experiments were conducted considering two camera models and demanding technical solutions for the illumination and layout constraints faced for the future implementation of GSI in IWT. To reduce into a linear pattern the enlarged defocused interference fringes, it is found that the optimal aperture of the slit is 5 mm. For the monodisperse droplet distribution, the results show discrepancies between the predicted and the measured diameters regardless of the sharp distribution of the occurrences of the droplet diameters. However, the dispersion found for the droplets generated by the conical nozzle exhibits the expected large variability. This effect is more emphasized when the imaged region is discretized in sub-windows, the number of droplets in each dramatically decreases, however compromising the results of the statistics. Different camera models and imaging configurations led to a variety of measurements at different spatial resolutions.