Flow structure measurement by beam scan type LDV

Abstract

A new type of laser Doppler vclocimeter called SLV (Scan-Type Laser-Doppler Velocimeter) which can measure the velocity field almost continuously and simultaneously has been developed and tested. The principle of the apparatus is to traverse the focal point of split laser beams by reflecting them with a rotating polygon mirror or an oscillating mirror which is driven (and controlled) by a stepping motor and to receive the scattered Doppler signals by a photomultiplier by focusing them through a cylindrical lens. The signals from the photomultiplier and the driving pulse of the stepping motor were transmitted to a personal computer and processed on-line.Experiments on the oscillatory boundary layer, Karman vortices. and vortex rings were carried out to check the performance.

Spatial filter velocimetry based on time-series particle images

“…The Nyquist frequency (Hino 1977) corresponds to n S = 2, and therefore, this result indicates the error occurs even when the sampling frequency is higher than the Nyquist frequency. The error, however, quickly decreases as the sampling frequency increases.…”

“…Scanning LDV systems (Durst et al 1981;Hino et al 1986;Lehmann and Mante 1991) have been developed to realize the multipoint measurement using an LDV system. Several studies have been carried out to develop LDV optics for simultaneous multipoint measurements (Nakatani et al 1980;Ikeda et al 1989;Maru et al 2010).…”