Measurement of Cavitation Nuclei Dispersion in Hydrodynamic Facilities

Cavitation nuclei populations are characterized by a stochastic distribution, both in size and dispersion within the flow domain. In order to statistically characterize the nuclei spatial distribution, a volumetric measurement technique based on use of Mie-Scattering Imaging (MSI) has been developed. Spatial characterization of nuclei concentration is achieved by jointly traversing a laser beam and a camera across the volume of interest, resulting in a two-dimensional matrix of line measurements, which are used to plot planar contours. A sample measurement of a nuclei plume is presented for a high Reynolds number flow over a backward facing step. The flow was seeded with a relatively large, nominally mono-disperse, nuclei population injected at a point on the step model surface. Con- tour plots of nuclei concentration in the wake of the step are presented for three streamwise and five spanwise planes. For each measurement position images were acquired until a statistically significant number of nuclei were detected (minimum of 500 bubble detections) or until 200,000 images were acquired. With such limit, the minimum resolvable nuclei concentration was of the order of ≈ 0.01mL−¹. The developed technique enabled successful characterization of an injected nuclei plume and provides another tool for rigorous modelling of nucleation in hydrodynamic facilities.