Study on unsteady separated flow and evaluation of aerodynamic admittance function

结构在自然风作用下的阵风响应分析中，假定来风脉动沿展向的相干性与各截面上的气动力沿展向的相干性是等价的。另一方面，风洞实验表明，气动力或表面压力表现出更多的相关特性。为了弄清相干性增加的机理，本研究对长细比B/D = 1（正方形）和5的二维矩形模型进行了表面压力和风速的测量。新安装了多点压力测量系统和三维周期流发生器。三维周期流发生器可以独立控制沿沿着的中部和两侧的正弦流频率，发现：（1）当B/D = 5时，分离流对展向相关性的增加起着最重要的作用。分离流重新附着在侧表面上 关于我们 从而形成分离泡。即使在三维周期性流动中，气泡也更二维地形成。表面压力的时间和空间分布表明，压力最大值向展向突然扩展，这可能会增加相干性。2）对于方形截面（B/D = 1），展向压力相关性再次被发现增加，但不如B/D = 5那么显著。分离流不能重新附着在侧面。这干扰了类似于B/D = 5中的分离气泡的封闭空间的形成。分离流的产生可能是导致展向相关性增大的重要因素。3）在风洞中研究了正弦流通过二维平板（B/D = 30）时的空间流场。在非定常薄翼型理论中，假定这种流型是持续保持的，这就产生了著名的Sears函数。为了捕捉迎面垂直风速和地面气压的正弦波动的失真程度，相位平均技术被应用到测量的行数据。结果发现，地面气压和垂直风速信号偏离正弦波显着。而上下压差基本呈正弦波。因此，确认假设成立。少

Gust response analysis of structures due to natural wind turbulence has an assumption on the equivalence of span-wise coherence of oncoming wind velocity fluctuation and that of aerodynamic forces on each section. Wind tunnel experiments reveals, on the other hand, that the aerodynamic forces or surface pressure appear more correlated properties. In this research project, to clarify the mechanism of the increase of coherence, surface pressures as well as wind velocity for the 2-D rectangular models of slenderness ratio B/D=1 (square) and 5 were measured. Pressure measurement system at multiple points and the 3-D periodic flow generator were newly installed. The 3-D periodic flow generator can control the frequency of sinusoidal flow in the mid part and the both side parts along model span independently.The following points were newly found:1) Separating flow plays most important role on the increase of spanwise correlation, in case of B/D=5. Separating flow reattaches on the side surfa … More ce to form the separation bubble. The bubble forms more two-dimensionally even in the 3-D periodic flow. Temporal and spatial distribution of the surface pressure demonstrates the sudden expansion of pressure maxima towards spanwise direction, which may increase the coherence.2) As for the square cross section (B/D=1), the increase of spanwise pressure correlation was again recognized but not so significantly as B/D=5. Separating flow cannot reattach on the side surface. Which interferes the formation of closed space similar to the separation bubble in B/D=5. The important factor for the increase of spanwise correlation may be the generation of separating flow itself.3) Spatial pattern of the sinusoidal flow during its passage through 2-D flat plate (B/D=30) was also investigated in wind tunnel. The pattern is assumed to be sustained maintained in the unsteady thin airfoil theory, which leads to the well-known Sears function. In order to capture the extent of distortion in the sinusoidal fluctuation of oncoming vertical wind velocity and surface pressure, phase averaging technique was applied to the measured row data. It was found that the surface pressure and the vertical wind velocity signal deviate significantly from sinusoidal wave. However, the pressure difference between upper and lower pressure indicated almost sinusoidal wave. Therefore, it was confirmed that the assumption is hold, consequently. Less