Research on aero-optical prediction of supersonic turbulent boundary layer based on aero-optical linking equation.

With the development of airborne imaging devices on the high-speed vehicle, aero-optical prediction of the turbulent boundary layer has attracted wide publicity. Based on the density distribution of supersonic (Mach 3.0) turbulent boundary layer obtained by nano-tracer-based planar laser scattering (NPLS) technique, we find that the time distribution characteristics of density fluctuation deviate from the Gaussian distribution mainly induced by the intermittency of a turbulent boundary layer. It may cause the prediction error of Sutton's linking equation to increase. The deflection-angle amplitude spectrum has a peak value at Stδ ≈1. With the increase of Stδ, the deflection-angle amplitude spectrum is more attenuated, which means that small-scale vortices make a relatively weak contribution to aero-optics, and which is mainly induced by large-scale vortices. With the assumption of locally homogeneous turbulence, the integral scale Λ is basically around 0.1δ. Without the assumption of locally homogeneous turbulence, the integral scale Λ is basically around 0.05δ. For the supersonic turbulent boundary layer with obvious inhomogeneity, based on the turbulence integral scale defined without the assumption of locally homogeneous turbulence, a fine aero-optical prediction result could also be obtained via the Sutton's linking equation. From the covariance distribution of density fluctuation, the prediction result based on the exponential distribution approximation is worse than that based on the Gaussian distribution approximation. The prediction effect is also shown through the change in coefficient. The prediction deviation of OPD based on the exponential distribution approximation is larger than that based on the Gaussian distribution approximation.