Simultaneous Velocity and Density Gradient Measurements using Two-Point Focused Laser Differential Interferometry

摘要

Two-point focused laser differential interferometry (two-point FLDI) is developed for making simultaneous measurements of velocity and density gradients in compressible flows. The technique is demonstrated in a canonical axisymmetric turbulent air jet (d = 3.2mm, M = 0.96 ± 0.03, Re = 8.5 ± 0.5 × 10~4,U = 306 ± 10m/s). Velocity and density gradients are measured at distances ranging from 1 to 50 jet-diameters downstream of the jet exit and at lateral distances ranging from -5 to +5 jet-diameters away from the jet centerline. Velocity magnitude, profiles, and phase fluctuations proportional to density fluctuations are consistent with other measurements in the literature. Turbulent wavenumber spectra are also reported. A lens calibration technique is introduced and implications of the size of the two-point FLDI measurement volume are critically examined.