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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。
The radiation flux received by the unit of infrared camera is analyzed. The analysis shows that the radiation flux difference between each unit of the infrared camera is only related to the radiation brightness of the transient field of view. Based on this, an infrared imaging simulation model of engine jet was developed. According to the position of the thermal imager and the jet, a jet stream cylinder envelope is established, and the line of sight of the instantaneous field of view is drawn from the unit of the plane array to obtain the intersection of the line of sight and the envelope. Radiation transfer equation was used to calculate the radiation brightness of the jet penetrating the line of sight. The non-uniform gas transmission rate was calculated by using Malkmus statistical narrow-band model combined with CG approximation. Then the radiation brightness is converted to gray level, and according to the pseudo-color coding, RGB values are assigned to the image pixels of each area array unit to obtain the jet infrared thermal image, and the pseudo-color coding adopts the rainbow coding. Finally, based on the jet flow of a certain type of engine, based on the hydrostatic pressure, the static temperature and the mole fraction of components, the infrared simulation images of the jet at the positive side are calculated. Infrared simulation images show that the model can accurately capture the nozzle is not fully expanded state, the jet inflatable wave and compress wave group caused by the local radiation brightness changes.