PIV技术在复杂二相流场中的应用

光学元器件随飞行器在大气中飞行时，其工作性能越来越多地受到大气悬浮汇聚微粒的影响。大气微粒在复杂流场中呈现何种运动汇聚效应，对于合理准确评估机载光学元器件的工作效能具有十分重要的工程意义，而复杂气动流场中微粒分布状态的预估一直是飞行器外界环境研究中的一个难点。气动问题的复杂性、大气中微粒的多样性一直是制约各种试验手段展开、数值模型建立的主要因素。利用先进的激光粒子图像技术，在风洞中对舵面旋涡主导的复杂流场中的微粒速度及分布特性进行了实验研究。在测量舵面翼梢脱落旋涡特性的基础上，通过激光片光扫描流场全域，同时高帧频CCD相机同步曝光，利用PIV 拍摄到的流场中涡流截面内微粒分布的瞬态图像。结合图像后处理技术，对原始粒子图像进行互相关、二值化处理，通过对图像区域内的灰度值计算，统计相对流场截面内的粒子浓度系数，得到在复杂旋涡结构流场内瞬态粒子的分布特性规律。研究结果表明，利用大气中微粒在激光片光下的米氏散射原理，可以有效地拍摄到复杂流场结构下粒子光学散射及分布的特性图像，解决了传统环境测试设备无法对复杂条件下流场内粒子分布进行实时测量的缺陷；在旋涡为主导的流场中，大气中的微粒由向心力牵引，在涡核周围达到平衡运动状态，微粒环绕涡核形成一条环状带，这一区域中的粒子浓度系数要远大于自由流场中的微粒，涡核中心粒子呈“空洞”状态。

The appliation of PIV technology in complex two-phase flow field

The performance of optics instrument was more and more affected by aerosols while it was flying with the aircrafts in the atmosphere.It has a quite important significance on the evaluation of optics working efficiency on the aircrafts that the particulates moved and pooled in complex vortex flow field.While the estimate of particulates in the atmosphere coupled with complex vortex field is always one of the most important problems in the research of aircraft envi-ronment.The complexity of aerodynamics and the diversity of atmosphere are always the main factors to restrict both the development of experiments and the foundation of the numerical mod-el.The distributing and velocity characteristic of particulate in complex vortex flow field was re-searched for the first time by advanced PIV technology in the low speed wind tunnel.Through the measurement to the vortex after the rudder,the instantaneous picture of distributing particu-late in the flow field was captured by PIV technology.The laser light scaning the flow field and exposure synchronization were used in the experiment.The instantaneous regularities of distribu-tion of particulate in complex vortex flow field was finally acquired through the image post pro-cessing technology,cross-correlation processing and gray scale calculating on original particulate picture.The result shows that by the principle of Mie scattering through the particulates in the laser light,the picture about the instantaneous complex vortex and particulate distribution can be captured by CCD camera,and by this it solved the limitation that traditional measurement equip-ments can not get the information of distribution of particulate in complex vortex flow in real time. In the flow field dominated by vortex,the particulate in atmosphere was pulled by centrifugal force,moved to balance and finally pooled to a loop around the core of the vortex.In this area,the coeffi-cient of particulate density is much larger than it in the free flow,and in the center of the loop,there is few particulate in the core of the vortex.