ABSTRACT |
A fibre optic three-dimensional Laser-Two-Focus(L2F)-Velocimeter was introduced in the Aircraft Aerodynamics Division in 1988. The former half of the present report describes both an outline and the principle of this system for two-dimensional measurements. In the latter half, the L2F-Velocimeter is evaluated by using three types of flows, i.e., two-dimensional wake, three-dimensional boundary layer and quasi two-dimensional free jet with, and occasionally without, seeding particles. Furthermore, several seeding particles such as paraffine vapor, mosquito-repellent smoke and tobacco smoke are used for evaluations. The axial velocity component from the L2F-Velocimeter is pointwisely compared with a calibrated velocity. The comparison is extended to the transverse mean velocity component/fluctuating components with hot-wire measurements, in which great care was taken with the linearity and wire inclination. There is no incongruity in comparison except in low turbulence with less than 2% intensity to the lal velocity .In summary, features of the fiber optic L2F-Velocimeter are its applicability to natural seed, wall-proximity and non-calibration measurements, although it is apriori known that the L2F-Velocimeter is not adaptable to both reverse flow and high turbulence measurements |