Large-Scale Aerooptical Distortions: Role of the Thickness of Turbulent Compressible Fluid Interfaces

Abstract

The interfacial-fluid-thickness (IFT) approach is extended to investigate the structure of high-gradient 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 flowgenerated 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. The new Aerooptics Pressure Vessel Facility enables the simultaneous measurement of density-field images and optical-wavefront images from a turbulent separated shear layer over a range of compressibilities (Mc 0.15 1.0) and at large Reynolds numbers (Re 10 6 10 8 ). The variations in interfacial fluid thickness or inverse of the local density gradient can be 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 highgradient networks corresponding to locally-thin interfaces, which dominate the large-scale aerooptical distortions on the basis of direct correlation between the measured optical wavefront distortions and the instantaneous flow structure. The IFT approach suggests a new way to physically describe and model both the flow structure and the aerooptical distortions at large Reynolds numbers and over a wide range of flow compressibilities.