Experimental studies of aero-optical properties of subsonic turbulent boundary layers

This paper gives the most-complete characterization to date of the optical aberrations imposed on a laser beam propagated through a subsonic, compressible, turbulent boundary layer in a zero-pressure gradient environment, over a range of boundary-layer thicknesses, oblique propagation angles and Mach numbers. This characterization is based on optical measurements using optical-wavefront-sensing instruments that have only become available in the last decade. The optical characterization includes and discusses in detail: optical-wavefront spectra, convective velocities of optically active large-scale structures and correlation functions in both streamwise and cross-stream directions, as well as root-mean-square optical path difference levels for different apertures. The scaling law based on the extended strong Reynolds analogy is derived and is shown to successfully collapse optical data collected in a number of facilities. Anisotropy of aero-optical distortions for different oblique viewing angles was experimentally quantified and is discussed.