Numerical simulation of infrared radiation characteristics of the B-2-like aircraft

  Objective  The B-2-like aircraft is the only active strategic bomber with excellent stealth performance in the world, and its low detectability is attributed to its unique radar absorbing coating and small radar cross section. However, the high-temperature gas from the exhaust plume cannot be directly concealed and eliminated, becoming a potential main source of infrared radiation. For B-2-like aircraft, the infrared radiation may comes from the high-temperature components such as the engine's high-temperature plume, skin, and nozzle. The exhaust plume of an engine often contains components such as CO₂, H₂O, and CO, which can emit intense infrared radiation at specific wavelengths through vibrotational transitions at high temperatures. In addition, the skin subjected to aerodynamic heating will also emit a continuous spectrum that follows Planck's law. This paper numerically analyzes the infrared radiation characteristics of the B-2 like aircraft at different observation angles under a representative flight condition (12 km@0.8 Ma), including the spectrum, integrated radiances, and synthetic IR image.

  Methods  Taking the B-2-like aircraft as the research object (Fig.3), the flow and thermal characteristic parameters of the engine nozzle are calculated by using the segmental specific heat method in the ideal gas state. The Navier-Stokes equation is solved based on the FVM method to obtain the flow field. The skin temperature is calculated based on the radiation equilibrium wall condition. Based on the statistical narrow-band (SNB) model, the physical properties of radiating gases are calculated, and the radiation transport equation (RTE) is solved using the light-of-sight (LOS) method. The Cartesian coordinate system is used to describe the radiation distribution in observation angles in 2π space, and the observation angle is described by the zenith angle θ and the circumference φ (Fig.5).

  Results and Discussions  The high-temperature regions of the aircraft is mainly located near the handpiece, air intake, engine compartment lid, and nozzle, with the highest temperature approaching 250 K (Fig.7). A significant afterburning effect occurs within a certain range from the nozzle, resulting in an increase of the plume temperature to 540 K, and an increase of the mass fractions of H₂O and CO₂ to 0.045 and 0.025, respectively (Fig.8). The spectral intensity of the skin is the highest in the top view with a peak value of 596 W/(sr·μm). The peak spectral intensity in the bottom view is 78.2% of that in the top view. The peak spectral intensity in the side, front, and rear views is similar, which is 12.8% of that in the top view (Fig.9). In the top view, the total spectral radiation intensity of the target is nearly 3 orders of magnitude higher than that of the skin, and the spectral peak value is in bands of 2.7 μm, 4.3 μm and 5-8 μm (Fig.12). The integrated radiation intensities of skin in the MWIR and LWIR bands are 8.2 W/sr and 1.9×10³ W/sr, respectively (Fig.10-11), and the total radiation intensity of the target is 1×10³ W/sr and 2.01×10³ W/sr (Fig.13-14). The maximum radiation intensity of the plume of the B-2-like aircraft in the MWIR band is approximately 2 times that of the LWIR band and four times that of the 4.3 μm band. In particular, the radiation intensity in the MWIR band is nearly three orders of magnitude higher than that in the 2.7 μm band (Fig.16).

  Conclusions  The radiation intensity of the B-2-like aircraft strongly depends on the wave band and observation angle, and the radiation intensity of the target is the strongest in the top view. The main sources of target radiation intensity in the MWIR band and the LWIR band are the exhaust plume and the aircraft body, respectively. This work can provide a theoretical reference for target characteristic identification of the B-2-like aircraft.