An Improved Reverse Monte Carlo Method for the Investigation of Aerodynamic and Infrared Radiation Characteristics of a Flying Wing UAV

Using the ray tracing algorithm to improve the reverse Monte Carlo (RMC) method, which is used to analyze the infrared radiation (IR) characteristics of the exhaust system, can greatly improve the computational efficiency and accuracy, and the calculation accuracy is improved by more than 8% compared with the original method. For a flying wing unmanned aerial vehicle (UAV), the influence of the geometry of the double S-shaped nozzles and the single S-shaped nozzles on the internal flow field were analyzed, then the influence of the internal and external flow on the aerodynamic performance of the S-shaped exhaust system, and the IR characteristics of the aircraft with different inlet and exhaust system in the 3μm-5μm and 8μm-14μm bands were studied.

The aerodynamic performance of the S-shaped nozzles under non-uniform inlet conditions are studied by numerical simulations and the corresponding flow field characteristics are analyzed. By studying the double S-shaped nozzles with different outlet shapes, the aerodynamic performance for varied geometric configurations is obtained and compared with the performance of the single S-shaped nozzles. The IR characteristics of the rear hemisphere on the single S-shaped nozzles and the double S-shaped nozzles were obtained, those nozzles have the similar engine matching performance. Because of the streamwise vortex and the secondary flow, the high temperature gas flow cannot form a local high temperature zone on the upper wall surface of the double S-shaped nozzle, resulting in a decrease of the radiation intensity of the nozzle by at least 65%, compared to the single S-shaped nozzle in the 3μm-5μm band. The aerodynamic characteristics of the flying wing UAV with the two S-shaped exhaust systems are also compared, and the changes in lift and resistance are analyzed.

The forward IR intensity of the flying wing UAV is significantly lower than that of the backward direction, and the upper direction IR intensity is higher than that of the lateral direction and the downward direction. Compared to the flying wing UAV with the single S-shaped exhaust system, the flying wing of the double S-shaped exhaust system has a lower IR intensity, for the peak intensity of the rear hemisphere in the 3μm-5μm band is reduced at least 70%, the maximum value of the locked distance is reduced to 25% of the UAV using the single S curved exhaust system. Since the flying Mach number of the flying wing is 0.8, and the temperature of the exhaust system is 400K~600K, the ratio of the amount of aircraft skin radiation to the total radiation increases from 30% in the 3μm-5μm band to more than 70% in the 8μm-14μm band. From the results of spectral analysis from 13μm-14μm, the mixing and cooling of the gas by the double S-shaped nozzle and the shearing effect of the airflow of the aircraft body make the gas temperature lower. The spectral radiance of the carbon dioxide absorption and emission band in the detector image is significantly less than that of the UAV with a single S-shaped nozzle.