Flow and Performance of Airfoils in Air-Water Two-Phase Flow

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As a basic research of two phase flow performance of turbomachinery, twodimensional flow around an airfoil and cascade of airfoils in air/water two phase condition was studies experimentally and theoretically. The results are summarized as follows:1. Construction of two-phase flow water tunnel Air/water recirculating water tunnel with test section of 200x100 mm, max. velocity of 8 m/s, mas. void fraction of 10 % was designed and built. Since no similar test tunnel has been built elsewhere, it required several testing and redesign of air injection device and reducing nozzle, before a satisfactorily uniform distribution of void fraction was obtained at the test section . Air is injected to water upstream of the reducing nozzle through 9 thin blades made of sintered powder metal. Both isolated airfoil and cascade of airfoils can be installed in the test section.2. Development of measurement system for local void fraction The system is composed of point electrode probe, x-y auto-traversing … More device and signal processor. Spatial distribution of void fraction and void size can be measured efficiently.3. Flow around an airfoil in two phase Flow flow around a NACA 4412 airfoil was measured for attack angle of 0 - 15゜and void fraction of 0 - 10 %. The spatial distribution of void fraction was measured by point electrode. Lift and drag characteristics were determined from pressure distribution over the airfoil. Due to the pressure gradient around the airfoil, the redistribution of bubbles occurs in such manner that bubble accumulate on the suction side while they are expelled from the pressure side. This gives rise to an unusual lift-attack angle characteristics.4. Numerical simulation Based on the dynamics of bubbles the basic equations of flow field were formulated, taking the slip between bubbles and surrounding water into account. The direct comparison between theory and experiment is still not complete and will be done in the near future.The study will be expanded to the case of cascade after the basic understanding is obtained on the two phase flow phenomena around an isolated airfoil. Less