水洞流场PIV显示与分析系统离轴测试校正

粒子图像测速技术(PIV)通过测量被测流场截面上每一位置点的速度,获得整个被测流场的信息.在PIV一般应用中所使用的照明激光片光与成像CCD装置的拍摄方向是垂直的,在某些应用场合受测试条件的限制,需要采用离轴方式进行测量,此时CCD成像方向与照明的激光片光不垂直,而是有一定夹角.离轴测试方式将对PIV系统的光学成像系统、示踪粒子选择和粒子图像处理带来影响.实验采用Scheimpflug离轴聚焦的方法对表面镀银高反射率的示踪粒子进行成像,通过调整成像透镜与CCD像面的夹角可获得清晰的粒子成像,并利用网格校正板和软件计算处理等方法有效校正了由于离轴测试带来的影响.

Off-axis Revise of PIV Watertunnel Flow Display and Analysis System

Particle image velocimetry(PIV) is a novel flow field measuring technology.PIV system takes picture of the flow tracer particles twice or more and use software processing the particles images.Then the velocity of each position in the measured area will be calculated then the whole flow field information in this area can be obtained.In PIV common use,the laser slice and the CCD screen orientation are vertical.For the limitation in some special application condition,off-axis detecting may be adopted,in which way the laser slice and the CCD screen orientation are not vertical.So in PIV off-axis detecting,the camera optical system,the tracer particle used and the particle image processing are different from PIV common use.To improve the system measurement precision in off-axis detecting,some methods are adopted.The tracer particles are wrapped with silver coating to improve the reflectivity.Scheimpflug focus,adjusting the angle between the imaging lens and CCD target to fit Scheimpflug condition,is used in the experiments to achieve high definition particles images.Then standard Grid board and the processing software are used to revise the images to display and analyse the measured flow field.