Calculation and experimental verification of radiation characteristics of spontaneous chaff clouds in high-speed flows

Abstract

When spontaneous chaffs diffuse in air, numerous radiations are shielded, absorbed, and reflected between chaffs, and there is interaction between the chaffs and the air. This makes it relatively complicated to calculate radiation transmission. To calculate the spatial distribution and generate radiation images of spontaneous chaffs, a radiation calculation model based on reverse path sampling was constructed which takes account of the transmission characteristics of radiation. This model hypothesizes that all detectors transmit light outward uniformly in the opposite direction of the radiation. After sampling statistics of light routes, the number and intensity of lights received by detectors along the radiation path were calculated. Next, a spontaneous combustion model of chaff was constructed. In this model, the effects of the porous structure of the chaff surface on the combustion rate of reactive metals are considered. The accuracy of this model was proved by comparing calculated results with experimental data. Finally, the spatial distribution of chaff clouds was calculated and their radiation images obtained. The results from the constructed model proved to be highly accurate when compared with measurement data from an experimental rocket sled.

目 的

当自燃箔片云团在空气中扩散时, 自燃箔片云团之间存在大量的对辐射的遮挡、 吸收和反射作用, 并且箔片与空气之间也会发生相互作用, 这使得辐射传输计算变得更加复杂。本文旨在计算自燃箔片云团的辐射特性并生成辐射图像。

创新点

建立自燃箔片云团的辐射计算模型和燃烧模型, 并得到辐射图像和光谱特性曲线。

方 法

• 1. 针对辐射的传输特点, 建立一种基于反向路径采样的辐射计算模型; 该模型假设探测器按照辐射的反向均匀向外发射光线, 采样统计各光线的路径后, 正向计算探测器接收到的光线数量与强度。

• 2. 考虑箔片表面的多孔结构对活性金属燃烧反应速率的影响并建立箔片的自燃模型; 将计算结果与实验数据进行对比, 验证该模型的准确性。

• 3. 计算得到箔片云团的光谱分布并生成辐射图像。

结 论

• 1. 箔片燃烧后温度迅速攀升, 并在 1.3 s 左右达到最大值; 随后, 温度缓慢下降, 并在 6 s 左右下降到接近环境温度。

• 2. 箔条云扩散后呈椭圆形, 扩散区随着时间的推移逐渐扩大, 且亮度中心向后移动。

• 3. 箔条云的光谱辐射强度极大点位于波长 1.4、 1.9、 3.1、 4.3 和 8.0 μm 处, 并且在 3.1 μm 时达到最大值。