Aperture Effects on Aero-Optical Distortions Caused by Subsonic Boundary Layers

Results of experimental measurements of aero-optical distortions caused by turbulent boundary layers at subsonic speeds M = 0.4...0.6 are presented. Measurements were performed using a high-speed Shack-Hartmann sensor and a Malley probe to collect instantaneous wavefronts with high spatial and temporal resolution. Effects of different aperture sizes on levels of aero-optical aberrations and correlation lengths in both spanwise and streamwise directions are compared and discussed for both wavefront sensors. Detailed statistical analysis of spatial and temporal spectra of aero-optical distortions is presented. Analytical method to predict levels of aero-optical distortions and streamwise correlation lengths for different aperture sizes is proposed and it was found to agree with experimental results. The contribution of boundary-layer largeand small-scale structures on overall level of aero-optical distortions is examined and discussed.