Study on the Discrete Vortex Method for Modelling Turbulent Flows

对离散涡方法作为湍流结构模拟方法的发展进行了研究，取得了以下成果。考虑到粘性扩散对涡量强度的影响，对斑点技术的涡模型进行了修正，使计算过程更加简单。通过对两个涡环相互作用的一系列试验计算，证实了改进的斑点技术不仅能较好地模拟两个涡环相互作用初期的连接过程，而且能较好地模拟两个涡环相互作用后的分裂过程。将改进的BLOB技术应用于球体绕流的数值模拟，结果表明，在起始流计算方面，较好地模拟了边界层与球体表面的分离、大尺度涡结构的形成以及尾迹流中三维特征的出现。对于压力波动的估计，提出了一种利用离散涡方法计算的瞬时速度场用边界元方法求解压力泊松方程的简单方法，并通过对圆柱和球体非定常流动的应用验证了该方法的有效性。将改进的旋涡方法应用于圆柱体、各种矩形柱体和后向台阶的流动模拟，得到了较为合理的结果，可望将改进的离散旋涡方法应用于各种工程领域的湍流分析，作为一种方便可靠的计算方法。

The study on the development of the Discrete Vortex Method as a modelling of turbulence structures has been carried out, and the following results were obtained.1. Taking account of the viscous diffusion effects on its vorticity strength, the vortex model of the blob technique was modified for a simpler procedure of calculation. From a series of test calculations of interaction between two vortex rings, it was confirmed that not only the connecting proscess of the two vortex rings at an early stage of the interaction but also the splitting process at the following stage were reasonably simulated by the modified blob technique.2. The modified blob technique was applied to simulation of a flow around a sphere, and it was obtained that the boundary layer separation from the sphere surface, the formation of large scale vortex structures and the appearance of three dimensional characteristics in the wake flow were reasonably simulated as far as the starting flow calculation was concerned.3. For the estimation of pressure fluctuations, a simple method was proposed to solve the pressure Poisson equation with use of the Boundary Element Method from an instantaneous velocity field calculated by the Discrete Vortex Method, and its usefulness was confirmed from its applications for unsteady flows around a circular cylinder and a sphere.4. The modified vortex technique was applied for the more reliable simulation of flows either around a circular cylinder and various rectangular cylinders, or over a backwards-facing step, and sutisfactorily reasonable results were obtained.From the results obtained the present study, it is expected that the modified Discrete Vortex Method presented here will be applied to analyze turbulent flows in various engineering fields as one of convenient but reliable calculation methods.