分析了红外热像仪面阵单元接收的辐射通量,该分析表明红外热像仪面阵各单元间的辐射通量差异只与其瞬时视场的辐射亮度有关.以此为依据,开发了发动机喷流的红外成像仿真模型.根据热像仪与喷流的位置,建立喷流的圆柱包络体,从面阵单元引出瞬时视场视线,求出视线与包络体交线.利用辐射传递方程计算了视线所穿透喷流的辐射亮度,其中非均匀气体透过率计算采用了Malkmus统计窄谱带模型结合CG近似的方法.然后将辐射亮度转换为灰度级,并根据伪彩色编码,对各面阵单元对应的图像像素点赋RGB值得到喷流红外热像,伪彩色编码采用了彩虹编码.最后,以某型发动机的喷流为研究对象,在流场分析给出静压、静温和组分摩尔分数的基础上,计算了正侧方两种距离下喷流的红外仿真图像.红外仿真图像表明该模型能够准确扑捉喷管处于不完全膨胀状态时,喷流的膨胀波和压缩波组导致的局部辐射亮度的变化.%Analysis of the radiant flux on the elements of the detector array of the IR camera has been done. It shows that the variance of the radiant flux on different element is due to the radiance in the corresponding instantaneous field of view (IFOV). Based on this conclusion, an infrared imaging prediction model of exhaust plume is developed. The model works as such : a cylinder which enclosure the exhaust plume is built first, then the path in the plume of the line of sight is found according to the position of the enclosure cylinder and IR camera. The radiance along the path is calculated by the radiative heat transfer equation. The model uses Malkmus band model and the Curtis-Godson approximation to study the transmissivity of inhomogeneous gas. After the radiance of all the IFOV detector elements is calculated , the relative radiance is assigned a gray level magnitude, and then is changed to the RGB value according to the rainbow color mapping function described in this paper. The RGB value of the detector element will then evaluate to its corresponding pixel in the final infrared image. A CFD simulation is conducted to provide the plume flow field parameters such as statistic pressure, statistic temperature and species molar concentration for a aero-engine. The predicted IR images for the camera at two different distance away from the plume at 90° aspect are obtained by the model. The image indicates that the model can capture the radiance variance caused by the expansion wave and compressed wave while the nozzle working at underexpanded state.
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