Development of highly accurate dynamic 3D-PIV based on digital holography and its applications

本研究开发了一种高精度的动态PIV技术，用单摄像机测量三维流场中的三个速度分量，并通过实验和数值模拟对其性能和测量精度进行了评价。该方法基于相干照明的数字全息术和摄像机。首先，建立了一个带有高速CMOS摄像机的光学系统，可以方便地捕捉到具有较高时间分辨率的示踪粒子的运动，并在三维空间中测量速度的三个分量。然后利用相对相位信息对观测到的全息图进行图像重建，以便在粒子数密度较高时区分示踪粒子。文中还提出了一种由重建的两个连续时刻的光强体积测量深度方向速度分量的新方法。速度分量的计算采用时空导数法。此外，将该方法应用于流体流动中漂浮的纤维状物体的三维方位测量。

In this research, a highly accurate dynamic PIV technique has been developed for measuring three velocity components in a three dimensional flow field with a single camera, and its performance and measurement accuracy have been evaluated by experiment and numerical simulation. The proposed method is based on digital holography with coherent illuminating light and a video camera. First, the optical system with a high-speed CMOS camera is set up to easily capture the motion of tracer particles with higher time-resolution and to measure three components of velocity in three dimensional space. Then the information of relative phase is employed for image reconstruction from an observed hologram pattern in order to distinguish tracer particles to each other at higher number density of particles. A new method is also proposed for measuring the velocity component in depth direction from the reconstructed volumes of light intensity at two sequential instants. The velocity component is evaluated by a spatio-temporal derivative method. Furthermore, the proposed method is applied to 3D orientation measurement of fibrous objects floating in fluid flows.