Experimental analysis of Separated boundary layer & measurement of void-fraction around the airfoil under two-phase flow conditions.

本研究的主要目的是阐明孤立翼型近表面区域内气泡运动与边界层分离的关系。首先，我们将这个目的划分为接下来的三个项目1。为了测量孤立翼面附近边界层中的空泡率，制作了一种新型的埋入翼型表面的光纤空泡率计。采用高速摄像机拍摄翼型表面附近流动中的气泡图像。阐明了翼型表面附近边界层中的气泡动因，并分别对各方案的结果进行了描述。研制了一种由光纤光电子器件、放大电路和个人计算机组成的新型局部含气率测量系统。并对该系统的性能进行了研究。但是，气泡反射光信号很弱，S/N比很差。因此，该系统的测量误差大于点电极探头的测量误差。必须进行更详细的研究。对图像的分析表明，气泡与边界层的相互作用、气泡在读出边缘附近的滑移运动等机理。为了观察气泡的浓缩过程，开发了图像处理软件，并通过实验验证了该软件的有效性。结果表明，在分离区内，流向主要流动方向的流动是由气泡形成的。通过测量翼型周围的压力分布和扩散器壁面的压力分布，证明了这一点。

The main purpose of this research is to clarify the relation between bubble motion and boundary layer separation in the region of near surface of isolated airfoil. At first, we divided this purpose to next three projects.1. To measure the void fraction in the boundary layer near the isolated airfoil surface, the new type void fraction meter which consists of optical fiber, buried the airfoil surface is made.2. The pictures which are bubbles in the flow near the airfoil surface, are took by high speed camera.3. The bubble motio in the boundary layer near the airfoil surface is clarified.In the following, the results of each project are described respectively.l. The new system for measuring of local void fraction I which consist of optical fiber photo electric device, amplifier circuits and personal computer, has exploited. And the ability of this system were studied. But, signal of reflected light from a bubble are very weak and S/N ratio is bad. Therefore, the error measured by this system is larger than the error measured by point electrode prob. More detailed studies must be necessary.2. The analysis of the pictures showed that the mechanism of the interaction between bubbles and boundary layer, that of slip motion of bubbles near the reading edge and so on. To observe the concentrating process of bubbles Image Processing Software are developed and it was shown to be useful.3. It is shown that the flow to the main flow direction in separation region are made by bubbles. This is proved by measuring both distribution of pressure around an airfoil and that of pressure on the wall of diffuser.