Study on unsteady separated flow and evaluation of aerodynamic admittance function

自然风湍流作用下结构阵风响应分析的假设是迎面风速度波动跨向相干性与各截面气动力相干性等效。另一方面，风洞实验表明，空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（平方）和5的二维矩形模型进行了地面压力和风速测量。新安装了多点压力测量系统和三维周期流量发生器。三维周期流发生器可以独立控制模型跨中部和两侧正弦流的频率。新发现如下：1)当B/D=5时，分离流对跨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，形成分离泡。即使在三维周期流中，气泡的形成也更加二维化。地表压力的时空分布表现为压力最大值向展向的突然扩展，这可能增加了相干性。2)对于方形截面（B/D=1），可以再次识别出沿展向压力相关性的增加，但没有B/D=5那么显著。分离流不能重新附着在侧表面上。干扰了封闭空间的形成，类似于B/D=5时的分离泡。展向相关性增大的重要因素可能是分离流本身的产生。3)在风洞中研究了正弦气流通过二维平板（B/D=30）时的空间分布规律。在非定常薄翼型理论中，该模式假定是持续保持的，这导致了众所周知的西尔斯函数。为了捕捉迎面而来垂直风速和地面压力正弦波动的畸变程度，对实测行数据采用相位平均技术。结果表明，地面气压和垂直风速信号与正弦波有明显的偏离。而上下压差几乎呈正弦波。因此，这个假设是成立的。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