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通过风洞实验研究了高宽比H/d=5的正方形棱柱顶部柔性薄膜颤振对柱体气动力特性的影响规律.模型宽度为40 mm,来流风速4~20 m/s,对应Reynolds数为10 960~54 800.柔性薄膜为厚度0.04 mm的高压聚乙烯膜,长度l=0.5~4 cm不等.实验发现,柔性薄膜的振动状态对三维方柱气动力特性有显著影响.低风速下,柔性薄膜不发生颤振,其对方柱气动力影响不大;随风速的增加,柔性薄膜发生颤振,方柱的时均阻力、脉动阻力和脉动侧向力最多分别减少约5%,25%和60%.柔膜发生颤振的临界风速随其长度增大而减小.只要柔膜发生颤振,其对柱体气动力的影响都是类似的,与其长度无关.流动可视化实验发现,薄膜的颤振改变了方柱绕流场,使柱体上半部分的反对称展向漩涡变为受膜拍动控制的对称结构,且越靠近自由端,此现象越明显. 相似文献
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有限长正方形棱柱绕流的双稳态现象 总被引:2,自引:0,他引:2
运用大涡模拟(large eddy simulation, LES) 方法对有限长正方形棱柱绕流进行了研究. 棱柱高宽比为5,一端固定于平板上,另一端为自由端. 平板表面边界层厚度可忽略不计. 基于自由流速度和棱柱宽度的雷诺数为3 900. 由计算结果发现,有限长棱柱的尾流在自由端后下扫流的作用下具有显著的三维性. 尾流中会交替出现两种典型的流动状态:一种是柱体两侧所脱落的涡在尾流中形成类似卡门涡街的交错排列状态;另一种是柱体尾流中涡团对称分布且无明显的周期性. 两种典型流动状态的交替出现,对有限长棱柱气动力特性有直接的影响. 相似文献
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The statistics of a passive scalar along inertial particle trajectory in homogeneous isotropic turbulence with a mean scalar gradient is investigated by using direct numerical simulation. We are interested in the influence of particle inertia on such statistics, which is crucial for further understanding and development of models in non-isothermal gas-particle flows. The results show that the scalar variance along particle trajectory decreases with the increasing particle inertia firstly; when the particle's Stokes number St is less than 1.0, it reaches the minimal value when St is around 1.0, then it increases if St increases further. However, the scalar dissipation rate along the particle trajectory shows completely contrasting behavior in comparison with the scalar variance. The mechanical-to-thermal time scale ratios averaged along particle, (r)p, are approximately two times smaller than that computed in the Eulerian frame r, and stay at nearly 1.77 with a weak dependence on particle inertia. In addition, the correlations between scalar dissipation and flow structure characteristics along particle trajectories, such as strain and vorticity, are also computed, and they reach their maximum and minimum, 0.31 and 0.25, respectively, when St is around 1.0. 相似文献
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