Experimental study on the aero-optical effects of a supersonic mixinglayer controlled by the ramp vortex generator array

As the main structure that induces aero-optical effects, the supersonic mixing layer is an essential structure in hypersonic flight vehicles with optical windows. The aero-optical effects of a Mc=0.17 supersonic mixing layer controlled by the ramp vortex generator array (RVGA) were investigated in detail using the nano-tracer-based planar laser scattering technique and ray tracing method. The incident locations and angles of the beam, and the mounting position of the RVGA, act as variables. In different cases, the optical path difference (OPD), Strehl ratio (SR), imaging displacement (ID), and bore sight error (BSE) are taken as evaluation parameters. Surprisingly, the length of the laminar section of the supersonic mixing layer varies little when the RVGA is applied. To reduce the aero-optical effects under our experimental conditions, the best incident angle is between 90º and 100º, and the position of the aperture should be carefully chosen to avoid the region of transition. A 10.75%-25.22% reduction of the average OPD_rms and a 15.30%-33.99% reduction of the standard deviation of the OPD_rms are achieved when the RVGA is applied, as well as an overall improvement of the SR, ID, and BSE. In our experimental circumstances, the supersonic mixing layer's aero-optical effects are suppressed to the full extent if the RVGA is mounted right at the trailing edge of the splitter.