Development of Advanced Turbulence Model for Prediction of Ship Stern Flow

计算流体动力学的最新进展使该技术在船舶流体动力学中的应用得到进一步的发展。然而，湍流模型仍然是准确预报船舶茎流的最重要的问题之一，其中通常涉及到强纵向涡。本研究的目标是发展新的湍流模型来克服这个问题。本研究历时三年完成，第一年主要研究了传统k-ε湍流模型的基本概念和修正策略。对新模型在相对简单的流场，平板边界层中的纵向涡流数值计算结果与实验结果的比较表明，新的湍流模型明显地提高了平均速度场的分辨率，但雷诺应力场的分辨率还不够理想。在第二、三年，新的湍流模型被应用于船舶流场计算，并进一步改进了模型，引入了非线性涡粘性表达式，总之，似乎能够更准确地预测雷诺应力场。此外，在最后一年，本模型的应用已扩展到内部流，即，直管中的循环湍流。通过上述评价，表明本湍流模型较传统的k-ε模型具有明显的优越性，并得出了一个重要的结论，即本研究项目的最初目标已经实现，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.