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

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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.