Characteristics of tomographic reconstruction of light-field Tomo-PIV

Abstract

Tomographic reconstruction of three-dimensional (3D) flow field is critical to achieve an accurate measurement of the complex flow field in tomographic particle image velocimetry (Tomo-PIV). Tomo-PIV based on the light field imaging has been used for 3D flow measurement due to its advantages of simple equipment system, low cost and overcoming the problems of complex synchronization and calibration of multi-cameras Tomo-PIV. However, the reconstruction quality such as the elongation and position error of the reconstructed particle, and the normalized correlation coefficient Q is closely related to the optical parameters of the light field camera, such as the inverse magnification and focal length of the main lens and the microlens, and the microlens pitch. Thus, the optimization of these optical parameters is desired for a better reconstruction quality. In this paper, the effects of these optical parameters on the light field image and reconstruction are numerically and experimentally investigated. In simulations, the light field images of the tracer particles are firstly generated for different the optical parameters by the ray tracing technique. The 3D tracer particle field is then reconstructed by the Expectation–Maximization (EM) algorithm. Simulation results show that the inverse magnification of the main lens and microlens, the focal length of the microlens, and the microlens pitch have important effects on the reconstruction quality, and thus the size and position of the measurement volume along the Z axis. Experiments are also carried out to verify the simulations. This study provides a basis for the optimization of the light field camera parameters for the accurate tomographic reconstruction of 3D flow field and the determination of the size and position of the measurement volume along the Z axis in the light field Tomo-PIV.