圆柱近尾迹流动转捩特征的数值研究

Numerical Prediction of Transition Features in Near Wake of a Circular Cylinder

本文用区域分解、杂交数值模拟方法研究Re＝3000圆柱绕流近尾迹中旋涡脱落及转捩波这两类不稳定性的时空发展与相互作用。速度功率谱分析所得的无量纲转捩波频率比ft／fs符合Re（0．87）关系，与Wei＆Smith实验结果一致，而与Braza等的数值预计的（Re（0．5））不同。分析计算了两种独立频率（ft，fs）的强非线性相互作用及由此产生的频谱拓宽并形成mfs±nft多级频带，表征流动的转捩特性。首次在理论上预计了转捩波与耦合频率强度沿尾迹下游的变化规律。

By means of a domain decomposition hybrid method transition features of the near wake flow behind a circular cylinder at Re=3000are studied in detail. The frequency ratio of the transition wave ft/fs is obtained by spectral analyses on velocities at various spatial positions downstream. The present result is first shown very good agreement with the 0.87 power law of Reynolds number given by experimental study of Wei &Smith, rather than the law of Re(0.5) and Braza's prediction. Development and the nonlinear interaction of two kinds of instabilities jz,fs leading to spectral broadening and generation of new predominant frequencies of mfs±nft are analy zed, showing the behaviours of flow transition. Longitudinal variation of the transition wave and the monlinear interaction are predicted.