Abstract
In this study, we apply the optical flow method to the time-series shadowgraph images of impinging jets using a high-speed video camera with high spatial and temporal resolution. This image analysis provides quantitative velocity vector fields in the object space without tracer particles. The analysis results clearly capture the details of the coherent vortex structure and its advection from the shear layer of the free jet. Although the results still leave challenges for the quantitative validation, the results show that this analysis method is effective for understanding the details of the physical phenomenon based on the quantitative values extracted from the shadowgraph images.
Highlights
Particle Image Velocimetry (PIV) [1] [2] and Molecular Tagging Velocimetry (MTV) [3] have been widely employed for optical, quantitative, and non-contact surface or spatial fluid analysis
This study aims to extract a quantitative velocity vector field by the image analysis for these well-known characteristic vortices captured by the shadowgraph method
In order to extract quantitative velocity vectors by image analysis without using tracer particles, we applied the optical flow analysis based on the physical relationship between the density change and the brightness change to the time-series shadowgraph images of the impinging jet
Summary
Particle Image Velocimetry (PIV) [1] [2] and Molecular Tagging Velocimetry (MTV) [3] have been widely employed for optical, quantitative, and non-contact surface or spatial fluid analysis. The development of three-dimensional velocity distribution measurement using stereo PIV has been remarkable with the rapid evolution of cameras and PC performance [4]. In the fluid analysis method using tracer particles, fluid analysis methods such as PIV using tracer particles have some problems, i.e. traceability of the tracer particles at high speeds accompanied by shock waves. As conventional qualitative optical visualization methods, the shadowgraph and schlieren optical visualization methods without tracer particles have been applied to understand high-speed flow phenomena with large changes in density.
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