Chevron Nozzle Performance Characterization Using Stereoscopic DPIV

Abstract

Stereoscopic Digital Particle Image Velocimetry (DPIV), having become a well- established technique for the measurement of the three-components of velocity within a fluid plane, was used to characterize the flow fields from a parametric test matrix of five chevron, plus one baseline circular, 50.8 mm diameter nozzles. Nozzle jet operating conditions ranged from acoustic Mach numbers of 0.9 to 1.5, with static temperature ratios ranging between 0.84 and 2.7. Detailed surveys of the single jet flows were performed to capture three- dimensional features of the turbulent exhaust jet evolution. Cross-flow planar measurements were obtained at twelve locations, ranging from 0.1 to 20 nozzle diameters downstream of the nozzle exit planes. Streamwise measurements, along the jet centerlines, were obtained at ten partially overlapping downstream locations, providing complete axial surveys over a region extending beyond 20 nozzle diameters downstream of the nozzle exit planes. In both optical configurations, the measurement planes were sized to completely capture the fully turbulent jet shear layer growth. The measured three-dimensional mean and turbulent velocity fields, along with computed second order statistics including axial vorticity and turbulent kinetic energy, were evaluated for all test points. Well-defined streamwise vortex structures in the jet shear layers are measured and reported. Examination of the relationships between chevron geometric parameters and flow characteristics is performed. Observed trends differentiating characteristic flow fields between hot and cold setpoints are noted. Evaluations of the stereo DPIV processing methodologies are made in an effort to establish confidence levels and highlight any limitations inherent in stereo DPIV measurements used for aeroacoustic performance characterization.