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Clarification of spatial and temporal coherent structure of pressure and velocity field around bluff body for evaluation of gust response of structures

澄清钝体周围压力和速度场的时空相干结构，用于评估结构的阵风响应

基本信息

批准号：
15360240
负责人：
SHIRATO Hiromichi
金额：
$ 9.54万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

项目摘要

This research aims to clarify the spatial and temporal coherent structure of surface pressure filed on a bluff body and its relationship to the surrounding velocity fields with flow separation and reattachment. These information is to be contributed to develop the advanced aerodynamic admittance and the joint mode acceptance which are important for the evaluation of gust response of structures due to turbulent natural wind.The surface pressure on 2-D rectangular cylinders with side ratio B/D=5 and 1 (B : width of cross section, D : depth of cross section) were measured at various position on side surface, simultaneously in turbulent and in smooth flow. Velocity field surrounding the bluff body, which consists of separating shear layer, flow reattachment on body side surface, were also measured at two different points by hot-wire anemometers.In the first year, the similarity between the aerodynamic admittance (equivalent Sears function) and the frequency transfer function obtained by th … More e aerodynamic derivatives (equivalent Wagner function) was confirmed by measuring surface pressure of a B/D=5 rectangular prosm. The influence of body motion on the spanwise coherence of surface pressure was also investigated. Consequently, the coherence does not get any significant influence of body motion. And the aerodynamic gust force was confirmed to be treated independently from the self-excited force. In the second year, the spanwise extension of surface pressure fluctuation was investigated under wide range of reduced frequency of approaching vertical sinusoidal gust. The extending properties were found to be significantly depending on the reduced frequency. When the reduced frequency is nearly equal to the characteristic frequency of the shear layer instability, where the shear layer instability is enhanced most sensitively by the external stimulation, the extension towards spanwise direction was not clearly captured. On the other hand, when the reduced frequency is relatively lower, the pressure fluctuation seemed to be transported more smoothly to the spanwise direction. Therefore, it was concluded that the increase of spanwise coherence of a gust force on a 2-D cross section comparing to the coherence of approaching flow velocity is mainly realized in lower reduced frequency region. In the last year, surface pressure field and the velocity field near a rectangular cross section were decomposed to the POD modes in smooth and in turbulent flow. As a result, the contribution rate of the non-uniform modes (the POD mode shape indicates non-uniform along spanwise direction) of the surface pressure was increased more in turbulent flow because of the non-uniform velocity distribution. Whereas, the non-uniform POD modes of the velocity field showed more dominant in turbulent flow. Therefore, the contribution rate of the uniform modes indicates relatively larger value for the pressure field than for the velocity field. And the formation of almost uniform separating shear layer from 2-D body controls the increase of the spanwise coherence of the 2-D gust forces. Less

本研究旨在阐明钝体表面压力场的时空相干结构及其与周围流动分离和再附着速度场的关系。这些信息将有助于开发先进的气动导纳和联合模式接受度，这对评估湍流自然风作用下结构的阵风响应具有重要意义。测量了边比为B/D=5、边比为1 （B：截面宽度，D：截面深度）的二维矩形圆柱体在侧表面不同位置，湍流和平稳流动时的表面压力。用热线风速计在两个不同的点上测量了由分离剪切层和体侧表面流动再附着组成的钝体周围的速度场。第一年，通过测量B/D=5矩形柱的表面压力，证实了气动导纳（等效Sears函数）与频率传递函数的相似性。研究了物体运动对表面压力展向相干性的影响。因此，相干性不受身体运动的显著影响。证实了气动阵风力与自激力是独立处理的。第二年，研究了在大范围减小的接近垂直正弦阵风频率下，地表压力波动的展向扩展。发现扩展特性显著依赖于降低的频率。当降低频率接近剪切层失稳特征频率时，剪切层失稳受外力刺激增强最敏感，向展向的扩展不明显。另一方面，当降频相对较低时，压力波动似乎更平稳地向展向传递。由此得出，相对于接近速度的相干性，阵风力在二维截面上的展向相干性增加主要是在降频较低的区域实现的。在去年的研究中，将矩形截面附近的表面压力场和速度场分解为光滑流动和湍流流动的POD模式。结果表明，在湍流中，由于速度分布的非均匀性，非均匀模态（POD模态形状表明沿展向不均匀）对表面压力的贡献率增加得更多。而在湍流中，速度场的非均匀POD模态更占优势。因此，均匀模态对压力场的贡献率要大于对速度场的贡献率。二维体上几乎均匀分离的剪切层的形成控制了二维阵风力展向相干性的增加。少