Aerooptical Interactions in Turbulent Compressible Separated Shear Layers and the Interfacial-Fluid-Thickness Approach

The interfacial-fluid-thickness (IFT) approach is extended to investigate the structure of highgradient regions of the density field and their eect on the aberrations of optical wavefronts in turbulent compressible separated shear layers. A new aerooptics facility was designed and built to allow simultaneous imaging of the density field and the flow-generated optical wavefront distortions. This novel facility consists of a main Aerooptics Pressure Vessel that has an inside diameter of 4 feet, an internal height of 8 feet, and it can be pressurized up to 20 atm. Benchmark testing of the new Aerooptics Pressure Vessel Facility enabled the simultaneous measurement of density-field images and optical-wavefront images from a turbulent separated shear layer at low-compressibility (Mc 0.15) and medium-compressibility (Mc 0.47) conditions. The variations in interfacial fluid thickness or inverse of the local density gradient were extracted from the density-field images in order to examine their direct eect on the propagation of optical wavefronts. One of the major benefits of using the IFT approach is being able to identify spatially isolated high-gradient networks corresponding to locally-thin interfaces, which were observed to dominate the large-scale aerooptical distortions on the basis of direct correlation between the measured optical wavefront distortions and the instantaneous flow structure. The high-gradient networks of the density field, and their eect on the optical wavefront distortions, are compared to the shear-layer mixing-field counterparts. The IFT approach suggests a new way to model the flow-generated aerooptical distortions at large Reynolds numbers for incompressible, low-, medium-, and high-compressibility flow conditions.