基于拉格朗日方法的水翼尾缘非定常涡旋结构研究

湍流中涡旋结构的非定常脱落是普遍存在的,其脱落规律的研究具有广泛的工程应用背景,探索有效的涡旋结构预测方法具有重大意义. 采用基于拉格朗日体系的有限时间李雅普诺夫指数方法对水翼尾缘附近涡旋结构的非定常发展过程进行研究. 采用大涡模拟方法对水翼周围湍流场进行计算,通过与实验结果进行对比,验证数值模拟方法的合理性与准确性. 并在此基础上,对水翼尾缘的非定常涡旋结构进行分析. 结果表明:尾缘涡旋非定常动态行为导致水翼动力特征准周期性波动. 有限时间李雅普诺夫指数方法可以准确描述尾缘涡的非定常流动细节,拉格朗日拟序结构可以捕捉水翼尾缘涡旋结构和尾迹涡街结构的边界. 

Lagrangian-Based Investigation of Unsteady Vertex Structure Near Trailing Edge of a Hydrofoil

Vortex shedding in turbulent flows is ubiquitous in our daily life and engineering applications. It is important to investigate the flow structures to predict their dynamical behaviors effectively. Lagrangian coherent structures (LCS) defined by the ridges of the finite-time Lyapunov exponent (FTLE) was utilized in this study to elucidate the time-dependent turbulent flows around a Clark-Y hydrofoil. The numerical simulation was performed with the commercial code CFX, and the turbulence modeling was carried out with the large eddy simulation (LES) approach in a classical eddy viscosity subgrid-scale (SGS) turbulence model. Comparing with experiment, the numerical simulation expressed its rationality and veracity. The results show that vortex shedding can lead to changes of pressure distributions near the trailing edge and the hydrodynamic fluctuations. The ridge of the FTLE field can form a LCS to represent a barrier between particles trapped inside the vortex region and those moving downstream. The results also indicate that the FTLE field has the potential to identify the unsteadiness of trailing edge vortex structures, and the LCS can capture the interface/barrier or the vortex region, such as trailing edge vortex and vortex street in the wake.