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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速度场的关系。这些信息将有助于发展先进的气动导纳和联合模式接受，这对于评估结构物在湍流自然风作用下的阵风响应是重要的。在湍流和光滑流动中，同时测量了侧面不同位置(B：横截面宽度，D：横截面深度)的二维矩形柱体的表面压力。用热线风速仪在两个不同的位置测量了钝体周围的速度场，包括分离剪切层和体侧表面的流动再附着。在第一年，气动导纳(等效西尔斯函数)与TH…得到的频率传递函数之间的相似性通过测量B/D=5的矩形螺旋桨的表面压力，证实了更多的气动导数(相当于Wagner函数)。此外，还研究了物体运动对表面压力跨向相干性的影响。因此，相干性不会对身体运动产生任何显著影响。确定了气动阵风力独立于自激力处理。第二年，在接近垂直正弦阵风的较大频率范围内，研究了地面气压脉动的跨向扩展。研究发现，扩展特性与降低的频率有很大关系。当折合频率接近于剪切层失稳的特征频率时，剪切层失稳最敏感的地方是外刺激，不能很好地捕捉到向展向的扩展。另一方面，当折合频率相对较低时，压力脉动似乎更顺畅地向展向传输。由此得出结论：二维断面上阵风作用力的展向相干性相对于接近流速相干性的增大主要是在较低的降频区实现的。在过去的一年中，将平面压力场和矩形截面附近的速度场分解为光滑和湍流中的POD模式。结果表明，在湍流中，由于速度分布的不均匀，表面压力的非均匀模式(POD模式形状表示沿展向的非均匀)的贡献率增加得更多。而在湍流中，速度场的非均匀POD模占主导地位。因此，均匀模式的贡献率对压力场的贡献率相对大于对速度场的贡献率。从二维体上形成的几乎均匀的分离剪切层控制了二维风阵力跨向相干性的增加。较少