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

研究了海崖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，这对评估结构在湍流自然风作用下的阵风响应是重要的。（B：横截面的宽度，D：横截面的深度）在侧表面上的不同位置处同时在湍流和光滑流中测量。用热线风速仪在两个不同的点测量了海崖体周围的速度场，其中包括分离剪切层、体侧表面的流动再附着，第一年用热线风速仪测量了钝体的气动导纳（等效Sears函数）和频率传递函数之间的相似性，第二年用热线风速仪测量了钝体的气动导纳（等效Sears函数）和频率传递函数之间的相似性。 关于我们 通过测量一个B/D=5的矩形截面的表面压力，证实了气动力导数（等效瓦格纳函数）。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任何显著影响。并将气动阵风力与自激力分开处理。第二年，在大范围的近似垂直正弦阵风折合频率下，研究了表面压力脉动的展向扩展。发现扩展性能显着取决于降低的频率。当折合频率接近剪切层失稳的特征频率时，外部激励对剪切层失稳的增强最为敏感，此时沿展向的扩展没有被清楚地捕捉到。另一方面，当折合频率相对较低时，压力脉动似乎更平滑地向展向方向传输。因此，得出的结论是，增加展向相干性的阵风力在二维横截面上相比，接近流速的相干性主要是实现在较低的约化频率区域。在过去的一年中，表面压力场和速度场附近的一个矩形截面被分解为POD模式在光滑和湍流。结果表明，在湍流流场中，由于速度分布的不均匀性，非均匀模态（POD模态的形状表示沿展向沿着的不均匀性）对表面压力的贡献率增大。而在湍流流动中，速度场的非均匀POD模态占主导地位。因此，均匀模态的贡献率对压力场的贡献率比对速度场的贡献率大。而与二维物体形成的几乎均匀的分离剪切层控制了二维阵风力展向相干性的增加。少

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