Abstract The present paper applied experimental and numerical methods to investigate the cavitating flow structures and corresponding hydrodynamics for a transient pitching Clark-Y hydrofoil. The aims are to (1) improve the understanding of the interplay between the transient cavitating flow structures, motion of the hydrofoil, and hydrodynamic performance, (2) quantify the influence of cavitation on the hydrodynamic load coefficients and flow structures, and (3) analyze the evolution of cavitating flow during different cavitation regime. The pitching motion trajectory is a triangular wave with mean incidence of α0=10° and amplitude of Δα = 5° at a frequency of 2 Hz. The upstream velocity U∞ is fixed at 6.3 m/s, which is corresponding to Re=4.4 × 105. The cavitation patterns for different cavitation numbers are mainly documented by the high-speed photography, and the dynamic characteristics of the hydrofoil are measured by the torque sensor. The numerical investigations were performed by solving the incompressible URANS equations using the mass-transfer cavitation model, the coupled k-ω SST turbulence model and γ-Reθ transition model. The predicted cavity patterns and moment coefficients agree well with the experimental results. Four typical regimes, including sub cavitation, inception cavitation, sheet cavitation and cloud cavitation, are observed. Compared to the sub cavitation case, the hydrodynamic coefficients and flow structures are significantly affected by the incipient cavity. Results show that the leading edge (LE) cavity promotes the formation of the counterclockwise tailing edge vortex (TEV), thus leading to decline of the lift. Moreover, the LE cavity also limits the formation of the clockwise second vortex (SV), which weakens the fluctuation of the hydrodynamic load. For the sheet cavitation case, three cavitating flow patterns(Pattern A/B/C) are observed in the hydrodynamic fluctuation stage, which is corresponding to different characteristic frequency. For the cloud cavitation case, the hydrodynamic curves present four distinct stages. According to the cavity breaking position and characteristic frequency, four different patterns(Pattern I/II/III/IV) of the cavity development and shedding are observed and analyzed.

中文翻译：

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瞬态俯仰水翼在不同空化状态下的空化流动结构和相应的流体动力学

摘要 本文应用实验和数值方法研究了瞬态俯仰克拉克-Y 水翼的空化流动结构和相应的流体动力学。目的是 (1) 提高对瞬态空化流动结构、水翼运动和水动力性能之间相互作用的理解，(2) 量化空化对水动力载荷系数和流动结构的影响，以及 (3)分析不同空化状态下空化流动的演变。俯仰运动轨迹是一个三角波，平均入射角为 α0=10°，振幅为 Δα=5°，频率为 2Hz。上游速度 U∞ 固定为 6.3 m/s，对应 Re=4.4 × 105。不同空化数的空化模式主要通过高速摄影记录，水翼的动态特性通过扭矩传感器测量。数值研究是通过使用传质空化模型、耦合的 k-ω SST 湍流模型和 γ-Reθ 过渡模型求解不可压缩的 URANS 方程来进行的。预测的腔体模式和力矩系数与实验结果非常吻合。观察到四种典型的状态，包括子空化、初始空化、片状空化和云状空化。与子空化情况相比，水动力系数和流动结构受初始空腔的影响显着。结果表明，前缘（LE）腔促进了逆时针尾缘涡（TEV）的形成，从而导致升力下降。此外，LE腔还限制了顺时针第二涡（SV）的形成，削弱了流体动力载荷的波动。对于片状空化情况，在水动力波动阶段观察到三种空化流型(Pattern A/B/C)，对应不同的特征频率。对于云空化情况，流体动力学曲线呈现四个不同的阶段。根据空腔破裂位置和特征频率，观察和分析了空腔发育和脱落的四种不同模式(Pattern I/II/III/IV)。LE 腔还限制了顺时针第二涡旋 (SV) 的形成，从而削弱了流体动力载荷的波动。对于片状空化情况，在水动力波动阶段观察到三种空化流型(Pattern A/B/C)，对应不同的特征频率。对于云空化情况，流体动力学曲线呈现四个不同的阶段。根据空腔破裂位置和特征频率，观察和分析了空腔发育和脱落的四种不同模式(Pattern I/II/III/IV)。LE 腔还限制了顺时针第二涡旋 (SV) 的形成，从而削弱了流体动力载荷的波动。对于片状空化情况，在水动力波动阶段观察到三种空化流型(Pattern A/B/C)，对应不同的特征频率。对于云空化情况，流体动力学曲线呈现四个不同的阶段。根据空腔破裂位置和特征频率，观察和分析了空腔发育和脱落的四种不同模式(Pattern I/II/III/IV)。对应不同的特征频率。对于云空化情况，流体动力学曲线呈现四个不同的阶段。根据空腔破裂位置和特征频率，观察和分析了空腔发育和脱落的四种不同模式(Pattern I/II/III/IV)。对应不同的特征频率。对于云空化情况，流体动力学曲线呈现四个不同的阶段。根据空腔破裂位置和特征频率，观察和分析了空腔发育和脱落的四种不同模式(Pattern I/II/III/IV)。