Spatial-temporal features of the coherent structure of sheet/cloud cavitation flows using a frequency-weighted dynamic mode decomposition approach

Abstract

To analyze the spatial-temporal features of sheet/cloud cavitating flows, a frequency-weighted dynamic mode decomposition (DMD) approach was proposed. A series of physical experiments with a cavitating flow around a NACA (National Advisory Committee for Aeronautics) 0012 hydrofoil were conducted with different cavitation numbers, where side- and bottom-view images of cloud cavitation were recorded by two high-speed cameras. Higher modes could be easily and clearly identified by analyzing the image differences between two adjacent snapshots in the time series recorded by the high-speed cameras. By assessing statistical two-dimensional cavitating flows around a hydrofoil, this work presents new insights on sheet/cloud cavitating flows. DMD results of the side-view snapshots showed that the shedding frequency increases with cavitation number, and the shedding behavior of sheet cavities with different lengths and frequencies can be uniformly described by a modified Strouhal number. The cavitating flows in bottom-view images are more complex and vary along the span. Different shedding patterns can be identified according to the aspect ratio of the cavity.