Optical Aberrations in a Subsonic, Compressible, Turbulent Boundary Layer

An experimental investigation of the physical cause of optical aberrations in a compressible, subsonic, turbulent boundary layer was conducted. X-wire, surface pressure, and optical data were collected to document the coherence lengths of coherent flow structures in all three coordinate directions in a turbulent boundary layer. These coherence lengths were measured to be on the order of the boundary layer displacement thickness, and together with the high convective speed of the coherent structures indicated that optically aberrating structures were located in the outer portion of the boundary layer. Conditionally averaging the velocity and surface pressure data based on minima in the OPD yielded a large-scale, coherent, vortical flow structure. This result provides a direct link between optical aberrations and large-scale, coherent, vortical structures (and their concomitant pressure wells) in the outer portion of a turbulent boundary layer.