非定常空化流动涡旋运动及其流体动力特性

采用大涡模拟方法对绕水翼云状空化的水动力特性和非定常流场结构进行研究. 基于实验结果对数值方法进行验证，分析空化与流场内部涡旋结构之间的相互作用以及对水翼动力特性的影响. 研究结果表明：大涡模拟方法可以准确模拟绕水翼流动的非定常过程. 在无空化条件下，升阻力系数存在斯特劳哈数St = 0.85 的主频波动，这是由水翼尾部涡旋结构的发展脱落引起的；在云状空化条件下，升阻力系数存在St = 0.34 的高能量密度低频波动，这是由大规模云状空泡团的发展和脱落引起的；云状空化阶段的升阻力系数在St = 0.5~1.5 的范围内都存在较高的波动，这是由于空化现象对水翼尾缘涡旋结构的发展和脱落产生影响，在不同发展阶段，空化现象不同程度地降低尾缘涡旋结构脱落频率.

STUDY OF TURBULENT VORTEX AND HYDRAULIC DYNAMICS IN TRANSIENT SHEET/CLOUD CAVITATING FLOWS

Studies are presented for a Clark-Y hydrofoil fixed at an attack angle of α=8° at a moderate Reynolds number, Re=7×10⁵, for both noncavitating and sheet/cloud cavitating conditions. The numerical simulations are performed via the commercial code CFX using a transport equation-based cavitation model, and the turbulence model utilizes the large eddy simulation (LES) approach with a classical eddy viscosity subgrid-scale turbulence model. The results show that numerical predictions are capable of capturing the initiation of the cavity, growth toward the trailing edge, and subsequent shedding, in accordance with the quantitative features observed in the experiment. The primary frequency, St =0.85, of the hydrodynamic fluctuations can be observed for noncavitation. It is induced by the shedding of the vortex structures at the trailing edge of the hydrofoil. The primary frequency, St =0.34, of the hydrodynamic fluctuations is induced by the growing up and shedding of the cavity, which can be observed for sheet/cloud cavitation. At the same time, some medium amplitude peaks are observed ranking from St =0.5 to St =1.5. These are due to the divergence influences from cavitation in different phases. These influences may lead to changes of vortex shedding frequencies at the trailing edge of the hydrofoil.