Aero-Optical Wavefront Propagation and Refractive Fluid Interfaces in Large-Reynolds-Number Compressible Turbulent Flows

摘要

The physical behavior of refractive fluid interfaces in turbulent compressible separated shear layers and the resulting structure of the aero- optical wavefronts have been investigated using new experimental studies and physical modeling. The experiments utilize the new AFOSR/UCI variable-pressure facility which generates large Reynolds number flows with elevated pressures in the test section crucial for direct imaging of the refractive field and interfaces. Direct, non-intrusive, and non-integrated imaging of the refractive index field in purely gaseous flows is achieved using laser induced fluorescence of acetone vapor molecularly premixed in air and recorded with a high-resolution intensified digital camera system, simultaneously with profiles of the propagated laser wavefronts recorded with a high-resolution Shack- Hartmann sensor. Three key accomplishments have been made. Firstly, direct examination of the aero-optical interactions at every location along the laser propagation path in the flow has been achieved. Secondly, a new aero-optical interaction mechanism has been discovered in which non-monotonic behavior of the cumulative aero-optical aberrations can occur depending on the location of the dominant refractive interfaces. Thirdly, significant resolution robustness has been observed for the effects of the refractive field on the laser aberrations. These three accomplishments are aimed toward the development of new directed energy capabilities for airborne vehicles.