Quad-cell cross-beam correlation for the investigation of high-velocity turbulence

摘要

Abstract: A nonintrusive experimental method, utilizing two Quad Cell detectors and a cross beam correlation (CBC) technique, was applied to Teledyne Brown Engineering (TBE) to investigate the relationship between fluctuating optical properties and image distortion caused by high velocity turbulence. A laboratory based Dual Nozzle Aero-Optic Simulator (DNAOS) was used to produce a mixing/shear layer that simulated a flight level aero-optic environment. Two Quad Cells were used to simultaneously measure the centroidal shift of two orthogonal laser beams that were located in a plane normal to the direction of flow and were coincident at only one point within the mixing/shear layer. The 2D angular deviations of the laser beams were calculated from the recorded centroidal fluctuations. From this data, the cross correlations could be calculated to determine the turbulence induced optical deviation (wavefront distortion) and density related index of refraction fluctuations for the flow field. The experimentally measured angular deviations were found to compare reasonably well to theoretically predicted values. This demonstrates that Quad Cell CBC can provide a nonintrusive method of accurately characterizing the fluctuating optical properties resulting from small scale hypersonic turbulent structures.!9