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Vorticity-based flow structures and cavitation evolution in high-pressure submerged waterjet
Author(s): Shuang Teng, Haixia Liu, C. Kang, Wenbin Zhang
Keywords: Submerged waterjet; TR-PIV; Flow structure; POD; Cavitation inception; Cavitation evolution
To investigate the flow structures and the cavitation phenomenon in the submerged waterjet, non-intrusive experiments were carried out. The waterjet was issued from a nozzle featured by a short straight segment of flow passage immediately upstream of the nozzle outlet. Jet pressures were varied from 5 to 22 MPa. The time-resolved particle image velocimetry (TR-PIV) was used to acquire flow velocity distributions. The proper orthogonal decomposition (POD) method was introduced to construct predominant flow structures based on PIV results. Cavitation inception was activated through increasing the jet pressure. A comparison of cavitation morphology for different jet pressures was implemented. Similarity in the distributions of averaged velocity is disclosed under various jet pressure conditions. POD results indicate that two high-vorticity bands near the nozzle, symmetrically distributed relative to the jet axis, dominate the jet flow. Further downstream, small vortex structures are sparsely distributed and assume a small percentage of the total jet energy. Initial cavitation manifests as small individual cavities which are generated near the high-vorticity zone. As the jet pressure rises, cavitation volume fraction increases but cavity geometry varies drastically with the jet progression. At later stage, stable cavity clouds are witnessed. During the entire process of cavitation evolution, high relevance between vorticity distribution patterns and cavity features is substantiated.