Abstract Time-resolved X-ray densitometry void fraction measurements and accompanying acoustic emissions have revealed that partial cavity shedding on a hydrofoil can be multimodal, with spontaneous changes in shedding sequence (referred to here as cavitation style) for fixed inlet flow conditions. These spontaneous, intermittent transitions between two physically different shedding styles are examined using data-based image analysis of the cavity flow fields in order to extract the associated physical mechanism leading to style transition. Three data-driven decomposition techniques are compared: proper orthogonal decomposition (POD), dynamic mode decomposition (DMD), and cluster-based reduced-order modeling (CROM), with a primary focus on the latter. The results highlight the utility of CROM over DMD and POD in the context of intermittent event analysis, both in terms of mode interpretability and transition mechanism identification. A frequency-based analysis of the CROM output revealed the existence of a shared harmonic between the different physical cavitation modes which gave further insight to the transition process. The data-based analysis ultimately illuminates the underlying flow mechanism that leads to the style transition, namely the key role of maximum cavity length buildup as it interacts with the vapor cloud collapse downstream of the hydrofoil. Graphic abstract

中文翻译：

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基于数据的多模态局部腔脱落动力学分析

摘要 时间分辨 X 射线密度测定空隙率测量和伴随的声发射表明，水翼上的部分空腔脱落可以是多模态的，对于固定的入口流动条件，脱落序列（此处称为空化样式）会发生自发变化。使用基于数据的腔流场图像分析来检查两种物理上不同的脱落样式之间的这些自发的、间歇的转换，以提取导致样式转换的相关物理机制。比较了三种数据驱动的分解技术：适当的正交分解 (POD)、动态模式分解 (DMD) 和基于集群的降阶建模 (CROM)，主要关注后者。结果突出了 CROM 在间歇事件分析的背景下在 DMD 和 POD 上的效用，无论是在模式可解释性还是转换机制识别方面。CROM 输出的基于频率的分析揭示了不同物理空化模式之间共享谐波的存在，这进一步了解了转变过程。基于数据的分析最终阐明了导致样式转换的潜在流动机制，即最大腔长积累的关键作用，因为它与水翼下游的蒸汽云坍塌相互作用。图形摘要 CROM 输出的基于频率的分析揭示了不同物理空化模式之间共享谐波的存在，这进一步了解了转变过程。基于数据的分析最终阐明了导致样式转换的潜在流动机制，即最大腔长积累的关键作用，因为它与水翼下游的蒸汽云坍塌相互作用。图形摘要 CROM 输出的基于频率的分析揭示了不同物理空化模式之间共享谐波的存在，这进一步了解了转变过程。基于数据的分析最终阐明了导致样式转换的潜在流动机制，即最大腔长积累的关键作用，因为它与水翼下游的蒸汽云坍塌相互作用。图形摘要