基于小波方法的肥大船尾流大涡模拟研究

The ship wake produces the complication of ship turbulent flow. Ship wakes contain complicated vortex structures in uniform and unstable distribution, which induces to obvious unsteady hydrodynamic performance of ships, especially full hull form.Accurate simulation of ship wake closely associates with the prediction precision of propeller's hydrodynamic performance, vibration & noise and wave induced motion of hull. Furthermore, it is highly significant to propeller's optimization design.RANS is inappropriate to simulating unsteady vortex structures. Therefore, it is necessary to employ LES although LES bears large computing load for boundary layer.This study advances a new model for the subgrid stress in wavelet multi-scale form, which is based on the match of wavelet's mathematical properties and turbulence's key physcal characters. The adaptive algorithm is proposed to promote the new model's efficiency. This method is applied to LES for simulating full hull's wakes. For quick verification and rectification, the turbulence around circle cylinder and ellipsoid is simulated with this method. Successively, this research simulates the turbulence of a full hull and this simulation is compared to experimental result and an uncertainty analysis is also carried out for model and algorithm's confidence analysis. In this study, several motions of the hull are in consideration, respectively.

船舶湍流的复杂性主要体现在船尾流场中，尾部流场具有十分复杂的涡系结构，它们分布不均匀且不稳定，导致船舶水动力性能具有明显的非定常特征，这种情况在肥大船型中尤其明显。船尾流场的准确数值模拟，关系到螺旋桨水动力性能、噪声与振动和船体运动响应的预报精度，对螺旋桨优化设计有着十分重要的意义。雷诺平均方法不再适合非定常流场的数值模拟，有必要采用大涡模拟方法，但它受边界层内的计算量限制。本研究基于小波数学性质和湍流关键特征的互相匹配，提出小波多尺度形式的亚格子应力的新模型，并建立相应的自适应算法以提高计算效率，把它应用在肥大船型的尾流大涡数值模拟中。为快速检验并能修正模型，先应用于圆柱及椭圆柱的绕流，然后模拟某肥大型船在各种船体运动姿态下的尾流场，与试验结果比较，对误差做不确定性分析，从而给出模型和算法的可信度分析。

大涡模拟是目前船舶水动力计算方面的前沿性的先进方法，借助该方法可以获得船舶流场的小尺度涡旋尺度结构信息，为精细计算船舶水动力计算提供了充分的数据支持。本项目基于小波多尺度分析与船舶湍流涡旋结构多尺度特征之间的关联，建立了小波多尺度分析的亚格子应力模型，并提出了小波自适应数值计算方法，应用于船舶流场大涡模拟计算。本项目的研究内容包括：基于小波方法的船体曲面表达；小波多尺度亚格子应力模型的建立；基于新模型的小波自适应方法；基于小波分析的兴波阻力船型优化；基于OpenFOAM平台的新模型下DTCHull船型的初步计算；船舶尾流中逆压梯度边界层情况下湍流模式的适用性研究。通过该项目研究，拓展了小波分析在船舶水动力方向的应用，并为船舶水动力数值计算实现了大涡数值模拟提供了一种可能途径，该研究在船舶水动力数值计算方面具有重要的科学和工程价值。