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

本文研究的主要目的是阐明隔振翼型近表面气泡运动与边界层分离的关系。首先，我们把这个目的分成了下面三个项目。为了测量靠近隔离翼型表面的边界层空隙率，研制了一种新型的由光纤埋入翼型表面的空隙率测定仪。图片是气泡在流动附近的翼型表面，采取了高速相机。澄清了靠近翼型表面的边界层气泡运动。下面分别描述了每个项目的结果。开发了一种由光纤光电器件、放大电路和个人计算机组成的局部空隙率I测量新系统。并对该系统的性能进行了研究。但是，气泡反射的光信号很弱，信噪比很差。因此，该系统测量的误差大于点电极探头测量的误差。必须进行更详细的研究。通过对图片的分析，揭示了气泡与边界层相互作用的机理、气泡在阅读边附近的滑移运动机理等。为了观察气泡的浓缩过程，开发了图像处理软件，并证明了它的实用性。结果表明，分离区向主流方向的流动是由气泡引起的。通过测量翼型周围的压力分布和扩散器壁面上的压力分布，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.