ABSTRACT

This study focuses on the correlative mechanism of the ambient pressure and inflow uniformity on the vortex and cavitation dynamics of an axial flow pump. The shear stress transport k – ω turbulence model and Schnerr–Sauer cavitation model are applied in the unsteady detached eddy simulation. The results show that the vortex merging between the primary and secondary tip leakage vortices (TLV) happens earlier with the growth of the cavity at a lower ambient pressure. The contact position of the merged TLV to the adjacent blade moves upstream with the decrease in the cavitation number. As the uniformity of the axial inflow decreases, TLV merging and vortex shedding are also promoted. The nonlinear variation of the initial angle of attack of the impeller blade leads to the compression or expansion of sheet cavitation under non-uniform inflow conditions. The evolution process and energy transfer of the vortices are verified quantitatively using a power spectral density analysis of kinetic energy fluctuations, and the short-wave instability leads to the fast decline of spectrum peaks at a higher frequency in the cavitating flow. It is crucial to avoid severe changes of ambient pressure and inflow uniformity to ensure the design performance of pump in actual working environment.

摘要

本研究重点研究环境压力和流入均匀性对轴流泵涡流和空化动力学的相关机制。剪应力传递k – ω湍流模型和 Schnerr-Sauer 空化模型应用于非定常分离涡模拟。结果表明，随着空腔在较低环境压力下的生长，初级和次级尖端泄漏涡流（TLV）之间的涡流合并发生得更早。合并的 TLV 与相邻叶片的接触位置随着空化数的减少而向上游移动。随着轴向流入的均匀性降低，TLV合并和涡流脱落也被促进。叶轮叶片初始攻角的非线性变化导致非均匀流入条件下片状空化的压缩或膨胀。使用动能波动的功率谱密度分析定量验证了涡旋的演化过程和能量传递，短波不稳定性导致空化流中较高频率的谱峰快速下降。避免环境压力和流入均匀性的剧烈变化对于确保泵在实际工作环境中的设计性能至关重要。