Large-eddy simulation of aero-optical effects in a spatially developing turbulent boundary layer

Large eddy simulations (LESs) of aero-optical effects in a turbulent boundary layer have been carried out at two Mach numbers (0.9 and 2.3) for an adiabatic wall boundary condition. This study is the continuation of previous work by the present authors using the temporal approximation. However, these temporal simulations have to cope with several drawbacks ( thickening in time of the boundary layer, no temporal average and under-resolved statistics). In order to compensate these limits, spatially evolving simulations are performed by means of an extension to compressible flows of the rescaling method of Lund et al. Within this configuration, a blur image caused by phase distortion is the main aero-optical aberration undergone by the wave front. This aberration is due to density variations in turbulent flow. First, aerodynamic fields are proved to compare favourably with theoretical and experimental results. Once validated, the characteristics of the boundary layer allow us to obtain information concerning optical beam degradation. The link between index-of-refraction fluctuations and phase distortion fluctuations is then discussed. Also, the density field is used to compute variance of phase distortion, on the one hand, directly and, on the other hand, by means of the optical models. Therefore, LESs allow us to study these models and the validity of their assumptions. Furthermore, contrary to the temporal approximation, spatially evolving simulations enable us to perform a spectral analysis of phase distortion fluctuations. Finally, LES is proved to be considered as a reference tool for evaluating aero-optical effects.