低雷诺数下两类柱体绕流的动力学模态分解  

Dynamic Modal Decomposition of Two Types of Cylindrical Flows at Low Reynolds Numbers

作　　者：王健 WANG Jian(Shanghai Construction Group Co.,Ltd.,Shanghai 200080,China)

机构地区：[1]上海建工集团股份有限公司,上海200080

出　　处：《建筑施工》2023年第10期2142-2148,共7页Building Construction

摘　　要：随着计算流体力学的迅速发展,基于特征提取技术的模态分解法已广泛应用于非定常流场的时空演化规律及流场机理研究。采用动力学模态分解法(dynamic mode decomposition,DMD),在雷诺数为100的条件下,分析了单方柱和单圆柱尾流卡门涡街发展的过渡阶段和稳定阶段的动力学特性,分别提取了两阶段两类柱体周围涡量场的子模态,分析并对比了各模态的频率及增长率,并进行了流场重构。结果表明:在过渡阶段,两类柱体的流场存在相同的内在结构—静态模态、卡门涡脱落模态、类卡门涡脱落模态、漂移模态和双倍频模态。其中静态模态代表了平均流场,卡门涡脱落模态及类卡门涡脱落模态分别对应2个阶段的卡门涡结构;此外,漂移模态的提取则体现了过渡阶段流场均值随时间的变化情况。在稳定阶段,DMD提取了稳定卡门涡街阶段的主要涡脱结构及其高次谐波模态,各模态均为周期性模态且增长率极小,随着频率的增大,模态相应的振幅及相干结构的尺度都减小。对比2个阶段的DMD结果发现,圆柱流场的主要结构在空间分布上更加接近背风面,其近尾流处的旋涡动态发展更加强烈。在重构相同精度的流场时,两类柱体皆在过渡阶段所需的DMD模态数更多,误差在空间分布上略有不同。With the rapid development of computational fluid dynamics,the modal decomposition method based on feature extraction technology has been widely applied to the study of the spatiotemporal evolution and flow mechanism of unsteady flow fields.The dynamic mode decomposition(DMD)method is used to analyze the dynamic characteristics of the transition and stable stages of the development of the Karman vortex street in the wake of a single square cylinder and a single cylinder under the condition of a Reynolds number of 100.The sub modes of the vortex field around the two types of cylinders in the two stages are extracted,the frequencies and growth rates of each mode are analyzed and compared,and the flow field is reconstructed.The results indicate that,during the transition phase,the flow fields of the two types of cylinders have the same internal structure-static mode,Karman vortex shedding mode,quasi Karman vortex shedding mode,drift mode,and double frequency mode.The static mode represents the average flow field,and the Carmen vortex shedding mode and quasi Karman vortex shedding mode correspond to two stages of the Karman vortex structure,respectively;In addition,the extraction of drift modes reflects the variation of the mean flow field over time during the transition phase.In the stable stage,DMD extracts the main vortex shedding structures and their higher-order harmonic modes in the stable Carmen vortex street stage.Each mode is periodic and has a minimal growth rate.As the frequency increases,the corresponding amplitude and scale of the coherent structure of the modes decrease.Comparing the DMD results of the two stages,it is found that the main structure of the cylindrical flow field is closer to the leeward surface in spatial distribution,and the dynamic development of vortices near the wake is more intense.When reconstructing the flow field with the same accuracy,both types of cylinders require more DMD modes during the transition phase,and the spatial distribution of errors is slightly different.

关 键 词：动力学模态分解 圆柱绕流 方柱绕流 数据驱动 卡门涡街 

分 类 号：TU311[建筑科学—结构工程]