大范围分离流动现象广泛存在于航空、航天、航海、风工程等领域。大分离流动通常表现出强烈的非定常旋涡脱落，伴随着气动噪声的产生，导致非定常气动力，甚至引起结构的振动而产生疲劳。DES类方法结合RANS和LES各自的优势，更适用于工程中大分离流动的数值预测。本文归纳了DES类方法发展的历程，基于k-ω-SST两方程湍流模型构造了DES、DDES、IDDES等方法，并分析了几种方法的构成特性和优缺点。基于均匀各向同性湍流衰减(DHIT)算例，标定了DES中的重要参数CDES；基于DHIT和串列双圆柱算例，研究格式耗散的影响：过大的格式耗散，使得解析湍流衰减过快，抑制分离区域小尺度结构，推迟表面流动分离，缩短压力频谱的频域解析范围。本文采用六阶中心耦合五阶WENO插值的对称TVD格式，为更好的预测小尺度湍流结构，构造了与DES类方法相匹配的自适应耗散格式。在该格式基础上，对比分析DDES和IDDES方法对串列双圆柱流动预测结果的影响：IDDES方法包含WMLES模型，能够反映来流边界层中湍流信息的作用，加快RANS到LES的转换，在圆柱表面的流动分离、圆柱之间区域湍动能分布的预测上较DDES方法更好。本文假设圆柱表面存在层流区，采用准层流假设（DDES-Quasi-Laminar）初步研究了转捩带对串列双圆柱流动的影响，发现由DDES-QL方法得到的后圆柱尾迹中的湍动能分布相比DDES方法更接近于有转捩带的实验结果。本文基于DDES和自适应耗散的对称TVD格式，研究了基本起落架(RLG)的非定常流动，给出表面压力、流线、压力均方根分布等表面特征，以及空间速度场，解析和模化的雷诺应力，瞬时空间涡结构等空间流场信息。计算表明，大部分计算结果与实验吻合较好。重点分析了表面特征之间及其与空间流动之间的相互关系，得到了表面最大声压级位于横轴底部和后轮近地侧靠内的位置，其产生原因均与来流非定常脱落涡的作用有密切关系。
Massive separation flows could be found in many fields such as aviation, navigation, spaceflight, wind engineering, and so on. Flows with massive separation always cause to unsteady vortex shedding which accompanies with unsteady force, generation of acoustics, and vibrations of solid frames which may lead to fatigue sometimes. Detached eddy simulation-type methods (DES-type), which combine the advantages of RANS and LES, are suitable for predictions of massive separated flows in engineering.Development of DES-type methods is summarized in this article, and the formations of DES, DDES and IDDES based on two equation k-ω-SST turbulence model are present. The characteristics, advantages and disadvantages of the above DES methods are analyzed in detailed. The key parameter CDES in DES-type methods is recalibrated through computing the decay of homogenous and isotropic turbulence case (DHIT). The effect on dissipation of spatial schemes is investigated through both DHIT and tandem cylinders cases. It suggests that excessive dissipation may speed up the decaying of turbulence, prevent the production of small-scale turbulent structures in the separated regions, suspend the flow separations from the surface, and shorten the range of power spectral density of pressure.A symmetric TVD spatial scheme, combining 6th center scheme and 5th WENO interpolation is taken as the spatial scheme when solving N-S equations. To capture more detailed turbulent structures, the dissipation of the scheme could be reasonable decrease depend on the flow fields, which is suitable for DES-type methods. Differences between DDES and IDDES when predicting the unsteady flows around tandem cylinders based on the adaptive dissipation scheme, are compared with experiments. The results show that IDDES including WMLES could reflect the effects of upstream turbulence information in the boundary layer, expedite the switch from RANS to LES, and take better performances than DDES on the locations of flow separation from the surface and the distributions of turbulent kinetic energy in the gap regions between the two cylinders. The effects of the transition trips on the cylinder surface are studied using DDES with quasi-laminar (DDES-QL) method initially. The differences could be found on the distributions of turbulent kinetic energy (TKE) in the wake of rear cylinder, and TKE based on DDES-QL matches the measurement with transition trip on the rear cylinder better.The unsteady flow past rudimentary landing gear (RLG) is investigated using DDES coupled with adaptive dissipation scheme. Features of surface flow such as distributions of mean and root mean square of pressure and friction lines and flow fields in space such as mean velocity, resolved and modeled Reynolds-stresses and instantaneous vorticity are obtained. The relation ship between the characters of surface flows and space flow fields is analyzed. The maximum sound pressure level (SPL) locates at the bottom side of the axle and ground inner side of the rear wheels which are related with the unsteady vortex shedding from upstream.
