Investigation of cavitation evolvement in a pump inducer by proper orthogonal decomposition analysis of video images

The aim of this study is to develop a contour extraction method for the investigation of the temporal and spatial characteristics of cavitation evolution in high-speed inducers. Cavitation experiments were conducted, and corresponding snapshots were captured using a high-speed camera subsequently. The raw images were processed while using threshold value filtering techniques to extract only relevant bubble information. Proper orthogonal decomposition was employed to explore the evolving characteristics in a quantitative manner. Results show that the cavitation evolution process is an unsteady process when viewed from the side. In high net positive suction head (NPSH) environments, multiple small-scale spatial modals contribute significantly to the effective proportion of the cavitation structure. The attached sheet cavitation exists in the blade edge which is the main embodiment of cavitation area evolvement. Under low NPSH conditions, the primary flow feature can be reflected by a low-mode flow pattern, associated with the inducer's rotation effect. The evolving regulation of cavitation area in developed stage is closely submitted to the trigonometric function. And the exhibited spatial coefficient exposes the hidden reflux vortex feature. The proposed image separation techniques enable the quantification of morphological features, which can provide technical details for the digital design of inducers.