Influence of optical aperture sizes on aero-optical effects induced by supersonic turbulent boundary layers

Abstract

With the increase of flight speed, aero-optical effects induced by the turbulent boundary layer near the optical window become increasingly significant. The density field of the supersonic (Mach 3.0) turbulent boundary layer (SPTBL) was measured by nano-tracer-based planar laser scattering technique, and the optical path difference (OPD) was obtained through ray-tracing method. The influence of the optical aperture size on the aero-optical effects of SPTBL was studied in detail, and the underlying mechanisms were analyzed from the perspective of the turbulent structure scales. The influence of the optical aperture on the aero-optical effects is mainly due to turbulent structures with different scales. The beam center jitter (sx¯) and offset (x¯) are mainly caused by turbulent structures larger than the optical aperture size, while the beam spread about the center (x′2¯) is mainly caused by turbulent structures smaller than the optical aperture size. With the increase of optical aperture size, the proportion of turbulent structures larger than the optical aperture size decreases, which can suppress the beam jitter and the beam offset. Meanwhile, since the beam spread is primarily induced by small-scale turbulent structures with relatively strong density fluctuation intensity, the spread increases rapidly to its peak and then gradually stabilizes as the optical aperture size grows.