COMBINED DIFFERENTIAL AND REFERENCE BEAM LDV FOR 3D VELOCITY-MEASUREMENT

A prototype near-backscatter reference beam laser Doppler velocimeter was developed for measuring the component of velocity along its line-o f-sight. It was used in combination with a previously commissioned sin gle colour rotatable differential Doppler velocimeter for the simultan eous measurement of axial and radial velocities near a model mounted i n a large water tunnel. This paper describes the reasons for adopting the reference beam method and the design principles that were employed . Sensitive signal processors were used and alignment problems were so lved by means of optical fibres. Line-of-sight velocities of up to 2 m /s were measured with the same precision as that in the transverse dir ections. Future detailed attention to the optical system would increas e the signal light flux and, thereby, enable faster flows to be measur ed. (C) 1997 Elsevier Science Ltd.