Optical Disturbances Caused by Transonic Separated Boundary Layer Behind a 20-Degree Ramp: Physics and Control

Abstract

In a previous paper [1], we documented the optical disturbance environment created by an attached turbulent boundary layer in high-Mach-number subsonic flow. In the earlier paper, an opticalaberration measurement instrument, the Malley probe, was described and used to collect a high-resolution time series of the optical aberrations for the boundary layer. In the present paper, results using the same instrument will be presented for a high-subsonic, turbulent boundary layer passing a downward 20 degree ramp. In this case, the flow becomes globally separated; the optical aberration environment upon separation starts at the level associated with the turbulent boundary layer but rapidly grows to a much higher level than for the upstream, attached boundary layer. Streamwise and spanwise measurements of Optical Path Difference (OPD) and local convective speeds of the opticallysignificant structures along the ramp were performed, along with velocity profiles. The objective of the work was to explore the use of passive devices to reduce the aberration environment created by the separating shear layer. A variety of