Mean and Fluctuating Property Measurements with Filtered Angularly Resolved Rayleigh Scattering

摘要

This paper details the simultaneous measurement of density, pressure, temperature, and the streamwise component of velocity in a supersonic free jet The free jet is a Mach 1.2 pressure-matched jet exhausted into atmospheric air. The nonintrusive measurement technique collects Rayleigh scattering from molecules created by a pulsed, frequency-doubled iNd: YAG laser across a range of angles in the plane of the jet exhaust. The laser can be tuned in frequency to transmit on a sloping absorption region of molecular iodine. The arc of the scattered light is focused through anamorphic optics, split into two beams, and captured on a single intensified charge-coupled device camera. One of the beams passes through a molecular iodine filter, and the other beam remains unfiltered. The Doppler shift and broadening characteristics of Rayleigh scattering are exploited to determine flow properties and a single component of velocity from a single laser pulse. Information from multiple pulses is combined to determine mean and fluctuating turbulent quantities. Results are presented in a plane perpendicular to the jet axis, located three diameters downstream from the jet exit. Additionally, lines of data that transit through the shear layer are presented at three, five, and seven diameters downstream. Mean measurements of density, pressure, temperature, and axial velocity taken near the jet exit agree with isentropic predictions within 5%, and measurements of property fluctuations follow flow features nicely. Turbulent velocity fluctuations measured appear to be biased by a constant value, although this bias is believed to be caused by limitations in the current instrumentation.