Influence of RVGA's height on suppressing the aero-optical effects induced by a supersonic mixing layer.

Abstract

The supersonic mixing layer formed on the surface of hypersonic/supersonic flight vehicles' optical windows is the main structure that induces aero-optical effects (AOEs), which may cause severe imaging degradation. Previous research has found that the ramp vortex generator array (RVGA) with a height of 1mm can suppress the AOE of a M c=0.17 supersonic mixing layer. In this paper, three RVGAs with different heights are considered. The nano-tracer-based planar laser scattering technique and ray tracing method are applied to do the aero-optical analysis. The root mean square of the optical path difference (O P D r m s ), Strehl ratio (SR), imaging displacement (ID), and angle deviation (AD) are taken as evaluation parameters. It is found that a smaller aperture size (A D ) corresponds to a better SR in the aperture size range of 5m m∼100m m. Then a beam with an incident angle α=15∘ and a 15mm A D is used to study the influence of RVGA's height on suppressing the AOE. When the RVGA is applied, the I D¯ and A D¯ (overline means time-averaged results) in different sections of the supersonic mixing layer are significantly normalized, which can simplify the AOE's correction procedure. The higher the RVGA is, the more the O P D r m s ¯ is reduced and the weaker the AOE is. RVGA1 (h=1.2m m) has the best performance in suppression of the AOE because it introduces much more disturbance than RVGA2 (h=1.0m m) and RVGA3 (h=0.5m m) and achieves better inhibition of the formation and development of the K-H vortices and more reduction of the whole thickness of the supersonic mixing layer.