主动射流控制水翼空化的数值模拟与分析

为了改善高速流动工况下水翼吸力面上流场的空化特性,提出了水翼表面主动射流对绕水翼周围流动加以控制的方法.基于密度分域滤波的FBDCM混合湍流模型联合Zwart-Gerber-Belamri空化模型,分析了来流空化数为0.83,来流攻角为8°,射流位置距水翼前缘为x=0.19c时,主动射流对于水翼吸力面上流动的空化特性和水动力特性影响.对回射流的强度进行了量化分析,以探究回射流与流场空化特性的关系.数值分析结果表明,在射流水翼吸力面上的时均空泡体积为原始水翼的1/15,使得流场内空化流动由云空化状态转变为较为稳定的片空化状态,显著地削弱了云空化的发展.此外,射流极大地改善了水翼的水动力性能,使得水翼的升阻比较原始水翼提高了22.9%,空泡的脱落频率减少了26.2%,空泡脱落所引起的振幅减小了9.1%.射流大幅降低了水翼吸力面上低压区面积,水翼吸力面上流体的逆向压力减小,回射流强度降低;同时,射流使水翼吸力面上的边界层减薄,增强了流动的抗逆压梯度能力,一定程度上阻挡了回射流向水翼前缘的流动,这也从机理上分析了主动射流抑制空化的原因. 

NUMERICAL SIMULATION AND ANALYSIS OF ACTIVE JET CONTROL OF HYDROFOIL CAVITATION1)

In order to improve the cavitation characteristics of the flow field on the suction side of the hydrofoil under high-speed flow conditions, a method of active water jet arranged on the suction side is proposed to control the flow around the hydrofoil. Based on a filter-based density correction turbulence model combined with Zwart-Gerber-Belamri cavitation model, the influence of the water jet on the cavitation and hydrodynamic characteristics of the hydrofoil is analyzed when the cavitation number is 0.83, the angle of attack is 8$^\circ$ and the water jet is 0.19$c$ from the foil leading edge. The intensity of the re-entrant jet is analyzed quantitatively to explore the relationship between the re-entrant jet and the cavitation characteristics of the flow field. The numerical results show that the time-average cavity volume on the suction side of the hydrofoil with jet is 14/15 smaller than that of the original hydrofoil, which indicate that the water jet can significantly weaken the development of cavitation, and thus the cavitation pattern in the flow field transforms from cloud cavitation to sheet cavitation. Moreover, the water injection greatly improves the hydrodynamic performance of the hydrofoil. The lift to drag ratio of the hydrofoil increases by 22.9${\%}$ compared with that of the original hydrofoil, meanwhile, and the shedding frequency of the cavitation decreases by 26.2${\%}$, and the amplitude caused by the shedding of the cavitation decreases by 9.1${\%}$. The water jet shrinks low pressure area on the suction side sharply and reduces the reverse pressure difference of flow in the vicinity of the hydrofoil, as a result, intensity of the re-entrant jet declined. The water injection also thins the boundary layer which enhances the anti-reverse pressure gradient capability of the flow and then blocks the re-entrant jet. Those explain the mechanism of cavitation flow control by active water injection.