Laser Doppler measurements in spatially restricted flows

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Abstract
Problems arising in the application of laser Doppler velocimeters to velocity fields of limited spatial extent, due to the necessarily finite sensitive volume of the velocimeter, are discussed with particular reference to fluid flow in narrow vessels with velocities of the order of a few cm s-1 and less. In this flow regime the greatest effect arises from velocity variations across the sensitive volume of the velocimeter. A simplified analysis is shown to be adequate in comparison with experimental results obtained using glass flow channels of widths varying between 0.9 and 5.4 times the length of the scattering volume.