Backward Monte Carlo method for simulating spectral radiation characteristics of boost-gliding vehicle

The boost-gliding hypersonic vehicle possesses unique features of high Mach number, high stealth, and high maneuverability, becoming a new air defense threat. The detection of its spectral radiation characteristics is one of the early warning ways. The study of spectral radiation characteristics is essentially a process of solving the Radiative Transfer Equation (RTE). Backward Monte Carlo Method (BMCM) is the most accurate method to solve the RTE compared with other methods, such as the Finite Volume Method and Line-Of-Sight method. In this study, numerical simulations of spectral radiation characteristics of an HTV2-shaped aircraft, at three trajectory points of 70 km, 50 km, and 30 km, are conducted using the BMCM. The incoming flow around the aircraft is calculated by a two-temperature OpenFOAM solver. In particular, a long-range detection model for the BMCM is developed to improve simulation efficiency. The absorption coefficients are calculated by the Line-By-Line method. Eventually, a code termed Plume Work Station-Radiation is developed to obtain spectral radiation intensities of an HTV2-shaped aircraft in the range of 1−15μm. Simulation results indicate that the high-temperature aircraft surface makes a vital contribution to the total spectral radiation characteristics, while the external flow field only has a finite contribution at some sensitive bands. The spectral radiation intensity at 50 km is the highest among the three trajectory points. An intersection point appears between the spectral radiation intensities of 70 km and 30 km due to the localized high-temperature surface at 70 km. The wavelength of the intersection point varies with the detector direction, which is attributed to the variation of the projected area of the high-temperature surface with the detector direction.