基于熵产理论的水翼空化特性研究

Study on Cavitation Characteristics of Hydrofoil Based on Entropy Production Theory

为了对空化流场中的能量损失做出定向、定量的评价,引入熵产理论对绕二维水翼流场进行了分析。以NACA0009翼型为计算模型,选用k-ω湍流模型以及ZGB空化模型对翼型的外特性进行了数值仿真并与实验结果进行了对比,发现计算结果与实验结果符合较好。仿真结果表明,熵产与翼型外特性之间有明显的相关性,在升力系数和阻力系数发生突变的时候,熵产和能量损失也发生剧烈变化;在流场中湍流耗散熵产始终占80%以上,大空化数下壁面熵产占比在10%左右,不可以忽略;能量损失总是集中分布在空穴的末端和翼型的尾端;空化数在0.6~0.4时,空穴会发生大尺度周期性脱落,造成流场的损失增大,但是当空化数<0.4时,空穴变得比较稳定,使得流场比较稳定,损失减小。分析表明,熵产理论可以应用于空化流场分析中。

In order to make directional and quantitative evaluation of the energy loss in cavitation flow,the entropy production theory was introduced to analyze the cavitation flow around a two-dimensional hydrofoil. The NACA0009 airfoil was chosen as the numerical model,the k-ω turbulence model and ZGB cavitation model were adopted to simulate the characteristics of the hydrofoil. The numerical results were verified by the experimental datas. The results show that there is a clear correlation between entropy production and airfoil dynamics,for the energy loss and entropy production change rapidly when the lift coefficient and drag coefficient change suddenly.The turbulent dissipation entropy production always accounts for more than 80% of the total entropy production,and in large cavitation number the wall friction entropy production accounts for 10% and so can not be ignored.The energy loss is centrally distributed at the rear portion of the cavity region and the trailing edge of airfoil.When the cavitation number is between 0.6 and 0.4,the cavity will shed periodically in large scale,leading to the higher energy loss generated in the flow field. However,when the cavitation number was lower than 0.4,the cavity is more stable and so the flow field becomes more stable and the energy loss decreases. The analysis show that the entropy production theory can be applied to the analysis of cavitation flow.