Investigation On The Aero-Optical Characteristics Of Flow Field Around High Speed Vehicle And Optical Window Design

For vehicles utilizing airborne optical devices, the high-speed flow field over the optical window causes several optical aberrations (bore sight error, blur, distortion, and jitter) of the images detected. These so called aero-optical effects severely degrade the detecting and tracking of the target, and make the optical seekers fail to function. To reduce the aero-optics effect, it is necessary to know the detailed aero-optical characteristics of the high-speed flow. In this thesis, based on the concept of integration design, a hybrid numerical method based on Reynold Average Navier-Stokes (RANS) and Direct Simulation Monte Carlo (DSMC) for high-speed flows was presented; a quantitative aero-optical evaluation method was established. Based on the methods mentioned above, the investigation on the aero-optical characteristics of high-speed flow field was carried out. Then the optimization design of optical window was carried out. The results attained are as follows.A hybrid RANS/DSMC numerical simulation method for high-speed flow field aero-optical analysis(RADAO), based on classic RANS/DSMC,was developed. The RADAO hybrid method is proved to be effective for the simulation of high-speed vehicles in various airspace and can satisfy the requirements of fluctuation information in the aero-optical analysis.An aero-optical evaluation method was established based on the concept of aerodynamical integration design. The refraction factor which can denote the aero-optical effects of flow field was derived. The quantitative evaluations which can represent the flow field's aero-optical performance were statistically obtained. This evaluation method, which can reveal the relation between the flow field's feature and its aero-optical performance, makes the aero-optics a potential part in the integration design of high speed vehicles.The characteristics of the high-speed flow field's aero-optical performance were investigated. The experimental schlieren pictures and numerical simulation results show that the high-speed flow field's aero-optical effects were caused by both mean flow field and fluctuation flow field. The aero-optical effects in mean flow field are much stronger than those in fluctuation flow field. Mean flow field's aero-optical effects are mainly distributed near the shock wave and boundary layer while the fluctuation flow field's aero-optical effects are mainly distributed in the boundary layer. The aero-optical performance will improve when the vehicle's angle of attack is greater and the mach number is lesser?The relation between window shape parameters and their aero-optical performance was analyzed. Various parameterized samples of different window shape were generated through design of experiment (DOE), the aero-optical performance of these samples was concluded. The parameter behaviors were investigated. This work is the basis of optical window design.The optimal design of optical window is obtained. The five parameter optimization design was carried out with the purpose of maximum aero-optical performance using Genetic Algorithms and kringing model. The final solution has a 15.97% improvement on the aero-optical performance compared to the original model.