粒子图像测速技术在拖曳水池中的应用

PIV Technique in Towing Tank

粒子图像测速技术 (PIV)在大型拖曳水池中的应用面临着很多困难 ,诸如 :水下激光片光照明、粒子图像捕捉、船舶流动的复杂程度、测量面积较大、粒子示踪、水下支架振动等。文章介绍了近十年来国内外PIV技术在拖曳水池中的应用和发展 ,对岸基式 PIV和随车式 PIV的优缺点做了比较与分析。还介绍了几个典型应用 ,即 6∶ 1椭球周围的速度及涡量分布的测量 ;不同尾附体连接形式的水下回转体伴流场测量 ;水面船首波流动结构的研究。文章还介绍了 Iowa大学对拖曳水池 PIV测量不确定度的评估研究。分析表明 ,国际水池

Many difficulties exist as PIV technique is applied in a large towing tank, such as laser sheet under water illumination, particle image capture, display of complicated ship flow, measurement of large area of flow field, suitable seeding particles selection, vibration of under water supporting strut, etc. It is quite a technical challenge to utilize PIV technique in a large towing tank. The paper introduces the development of PIV technique and its application in towing tanks in recent ten years. Two kinds of PIV in towing tanks, i.e., the stationary PIV and the towing PIV are presented, and each one's own advantages and disadvantages are analyzed. Three application examples are given. The first is the measurement of the velocity and vorticity distribution around an inclined 6∶1 prolate spheroid, in which the objective is to determine the effects of boundary lay tripping, incidence angle and Reynolds number on the flow structure. The second is the measurement of wake flow around an under water revolution body, among which there are two different junction forms of the stern appendages. The results indicate the fine difference of flow structure at the nominal wake plane could be discerned, which supplies important information to guide the design of appendages and the propeller. The third is the PIV measurements and free surface visualization around a ship model focused on the flow within the liquid sheet forming around the bow, the origin of the bow wave, variation in the structure of this wave at different distances from the model and the flow near the body downstream of the wave. The uncertainty assessment is done for IIHR towing tank PIV measurement system. Quantitative comparisons with 5 hole pitot data shows that PIV uncertainties are about 1% lower than those for 5 hole pitot.