An advanced laser-Doppler velocimeter for full-vector particle position and velocity measurements

Abstract

An advanced laser-Doppler measurement technique has been developed for fully resolved three-component particle position and velocity vector measurements in turbulent flows. The instrument deemed the ‘comprehensive’ laser-Doppler velocimeter employs a novel optical arrangement to measure multiple-component sub-measurement-volume-scale seed particle positions simultaneously with the velocity vector measurements of conventional laser-Doppler velocimetry (LDV). In the current paper, the effectiveness of the position resolution capabilities is considered, which allows for velocity statistics measurements at multiple locations within the measurement volume. Design estimates for the position vector uncertainties for a particle passing the measurement volume are about 3 µm root mean square in any direction, although in situ estimates indicate an uncertainty value closer to 14 µm with the possibility of further refinement through optimized alignment. To validate the operation of the instrument, measurements are presented in turbulent boundary layers previously examined with high-resolution conventional LDV. The flat-plate turbulent boundary layer is studied at two Reynolds numbers up to Reθ = 7500. Measurements are also presented in a pressure-driven three-dimensional turbulent boundary layer created beside a wing/body junction. These measurements illustrate the effectiveness of the technique for obtaining highly resolved velocity profiles within the measurement volume and give the highest spatial resolution velocity statistics published for Reynolds numbers of the magnitude studied.