Aero-optic distortion in transonic and hypersonic turbulent boundary layers

A two-dimensional Shack-Hartmann wave-front sensor is used to study aero-optic distortion in turbulent boundary layers at transonic and hypersonic speeds, with and without gas injection. The large-scale motions in the outer layer, of the order of the boundary-layer thickness in size, are shown to dominate the aero-optic distortion. Gas injection always reduced the Strehl ratio, with helium injection generally giving lower Strehl ratios than nitrogen injection. The large aperture approximation is shown to be accurate for a wide variety of aberrations regardless of Mach number and gas injection. A new scaling argument for the root-mean-square phase distortion is proposed that appears to collapse the data better than previous models.