Laser Doppler Velocimetry in Supersonic Round Jets

Abstract

Development of a laser Doppler velocimetry (LDV) system was undertaken for supersonic aeroacoustic laboratory measurements. Initial qualification of the system was undertaken by measuring subsonic jet exhaust flows. The mean velocity of the centerline of the jet was measured and compared to previous LDV studies. The axial turbulence intensity was also estimated and compared to previous LDV studies. The LDV system was then tested by measuring a near sonic and supersonic jet exhaust at over-expanded, under-expanded, and fully expanded conditions. The centerline mean jet velocity, axial turbulence intensity, probability density function, histograms, and power spectral density were all analyzed with comparisons made to previous studies. Similar measurements were made on the jet shear layer. The importance of proper seeding of both the core and entrainment flow was highlighted.