Error Analysis for Velocity Measurements in Rotating Flow using Large Scale Particle Image Velocimetry
Seojun Kim, Kwonkyu Yu, Byungman Yoon, Myeonghui Ahn
Thursday 2 july 2015
14:05 - 14:20h
at Africa (level 0)
Themes: (T) Special session, (ST) Acoustic monitoring of flow, turbulence and river discharge
Parallel session: 12F. Special session: Acoustic monitoring of flow, turbulence and river discharge
Recent advances in IT technology have enabled us to take advantage of modern instrumentations for stream flow monitoring. Among others, Large Scale Particle Image Velocimetry (LSPIV) that utilizes remotely recorded video imaginary has been considered as convenient and cost-effective tools compared with conventional surveying techniques such as mechanical velocimeter and float. Though the LSPIV technique has been highlighted for hydrologic communities in the last decades, the applicability in terms of its field operations has brought in several uncertain aspects. In particular, it is very crucial how to decide the size of interrogation area and time interval between images, since the LSPIV makes use of visible migration of surface particles to estimate flow velocity. Especially for the rotating flow, the rotating surface pattern driven by the rotating flow significantly changes particle density distribution when very large size or time interval were applied. Thus, the determination of an appropriate size of interrogation area and time interval should be more carefully considered than dealing with straight flow patterns. Before optimally deciding the size of interrogation area and time interval for the rotating flow, this study aims to provide error analysis accordingly with different rotation angle between two consecutive images driven by rotating flow and size of interrogation area. The results showed that, for the less than 4 degree of the rotation angle, the error noticeably decreased when the size of interrogation area became increased. Between 6 to 8 degrees of the rotation angle, however, the error adversely increased for the given size of interrogation area while the error decreased for the smaller size of interrogation area. Over 8 degree of the rotation angle, the error remarkably increased. These results indicated that the rotation angle of rotating flow significantly affects the accuracy of the LSPIV technique.
