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单相机动态PIV技术，用于三维流场中三个速度分量的测量，并通过实验和数值模拟对其性能和测量精度进行了评价。所提出的方法是基于相干照明光和摄像机的数字全息。首先，利用高速CMOS相机搭建光学系统，方便地以更高的时间分辨率捕捉示踪粒子的运动，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的情况下区分示踪粒子。本文还提出了一种从两个连续时刻光强重建体中测量深度方向速度分量的新方法。采用时空导数法计算速度分量。此外，该方法还应用于流体中漂浮纤维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.