The objective of this paper is to identify the dominant coherent structures within cavitating flow around a Clark-Y hydrofoil using two data-driven modal decomposition methods, proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD). A snapshot data sequence is obtained using a large eddy simulation and the interaction between cavitation and the vortex during cloud cavity shedding evolution is investigated. Modal decomposition via POD and DMD indicates that the dominant coherent structures include the large-scale cavity–vortex, re-entrant jet, shear layer, and small-scale vortex in the wake. In addition, the flow field can be reconstructed from the most energetic POD or DMD modes. The errors in the flow reconstructions produced using the first four POD modes, first eight POD modes, and first eight DMD modes are 3.884%, 3.240%, and 3.889%, respectively. Furthermore, transient cavitating flow can be predicted via the DMD method with an error of 8.081%. The largest errors in the reconstructed and predicted results occur mostly in the shear layer, trailing edge, and near wake. POD and DMD provide accurate and practically beneficial techniques for understanding cavitating flow, although substantial challenges remain with regard to predicting this intense nonlinear system.

The objective of this paper is to study flow-induced vibration in cavitating flow around a steel stainless hydrofoil with the experimental and dynamic mode decomposition (DMD) method. A synchronized measured system consisting of a high-speed camera, lift measurement, and laser Doppler vibrometer is used to observe the cavitation structures, survey the vibrations, and measure the force. The hydrodynamic force and vibration velocity fluctuate most sharply in the cloud cavitation stage among all the cavitation regimes due to the unsteady cloud cavity, corresponding to the largest square root of normal distribution in the cloud cavitation in the analysis of statistic nature. Cavity shedding frequency, system-related frequency, and trailing edge vortex shedding frequency are observed in the vibration velocity frequency spectrum for the whole range of cavitation numbers. Cavity frequency dominates the structure response in the cloud cavitation regime. Two primary shedding mechanisms, re-entrant jet, and shockwave mechanism are identified for the cloud cavitation. The vibration velocity induced by the re-entrant jet mechanism is lower amplitude and larger frequency, while that induced by the shockwave mechanism is higher amplitude and smaller frequency due to the intense collapse of cloud cavity and rapid collapse of the attached cavity. Two peak bands related to the re-entrant jet development frequency and small-scale cavity shedding frequency are identified for the shockwave mechanism with DMD method.