Development of Advanced Turbulence Model for Prediction of Ship Stern Flow

计算流体力学的最新进展使该技术在船舶流体力学中的进一步应用成为可能。然而，湍流模型仍然是准确预测船舶干流的最重要的问题之一，其中通常涉及强纵向涡。本研究项目的目标是开发新的湍流模型来克服这个问题。完成目前的工作用了三年时间。第一年主要研究了k-ε湍流模型的基本概念和修正策略。新模型在相对简单的流场中进行了初步验证，即平板边界层纵向涡旋流场。数值结果与实验数据的详细比较表明，该模型明显提高了平均速度场的分辨率，尽管雷诺应力场的分辨率有些令人不满意。在第二年和第三年，新的湍流模型应用于船舶流动计算，并对模型进行了进一步修改，引入了非线性涡流黏度表达式，可以更准确地预测雷诺兹应力场。此外，在最后一年，本模型的应用已经扩展到内部流动，即直管内的循环湍流。通过上述评价，表明当前湍流比传统的k-ε模型具有明显的优势，从而得出一个重要的结论，即本研究项目的最初目标已经实现，并取得了令人满意的成果。

The recent advancement of computational fluid dynamics has enabled further application of the technique to ship hydrodynamics. However, turbulence model has still been one of the most important issues for accurate prediction of ship stem flow, where strong longitudinal vortices are normally involved. The objective of the present research project is to develop new turbulence model to overcome the problem. Three years had been used to complete the present work.In the first year, main focus was placed on investigation on basic concept and strategy to modify the conventional k-ε turbulence model. Initial validation of the new model was done in application to relatively simple flow filed, i.e., longitudinal vortex flow in flat plate boundary layer. Detailed comparison of the numerical results with experimental data indicated that the present model clearly improved resolution of the mean-velocity field, although that of Reynolds stress fields was somewhat unsatisfactory.In the second and third years, the new turbulence model had been applied to ship flow computation, in conjunction with further modification of the model associated with introduction of nonlinear eddy viscosity expression, which had, in conclusion, appeared to be capable for more accurate prediction of Reynolds stress fields. Furthermore, in the final year, application of the present model had been extend to internal flow, i.e., circulatory turbulent flow in a straight pipe. Through the above-mentioned evaluations, the present turbulence had been shown to offer evident advantage over the conventional k-ε model, and that leads to an important conclusion that original goal of the present research project had been achieved with satisfactory accomplishments.