类B-2型飞行器红外辐射特性数值模拟

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

类B-2型飞行器因其独特的气动布局和较强的隐身能力,成为攻防对抗和预警探测识别工作中重点关注的目标之一。通过构建类B-2型飞行器的气动外形,基于真实可压缩气体模型和辐射平衡壁面边界条件预测典型飞行工况(12 km@0.8 Ma)下的绕流场、尾喷焰和壁面温度,结合窄谱带高温气体辐射物性数据库,采用视在光线法求解辐射传输方程,获得不同观测角度、不同波段条件下目标本体和尾喷焰的红外辐射特性。结果表明:类B-2型飞行器在俯视观测角度下辐射强度最强,本体在长波波段内的辐射强度较中波波段高出近两个量级。中波波段内目标辐射强度主要来自尾喷焰,长波波段内主要来自本体。研究可为类B-2型飞行器的目标特性识别提供理论参考。

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 2πspace,and the observation angle is described by the zenith angleθand the circumferenceφ(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 2.7μm,4.3μm and 5-8μm(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 4.3μm band.In particular,the radiation intensity in the MWIR band is nearly three orders of magnitude higher than that in the 2.7μm 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.