Rapid prediction model for tail infrared radiation characteristics of serpentine nozzles

To efficiently calculate the infrared radiation characteristics of serpentine nozzles with varying shielding properties during the early stages of infrared stealth design for exhaust systems, a rapid prediction model for the tail infrared radiation characteristics of serpentine nozzles has been developed. This model combines the image-based method and the one-dimensional flow field model. The former transforms the geometric shielding relationship of serpentine nozzles into pixel operations on multi-layer two-dimensional images, and the latter is established based on the compressible pipe flow and jet theory. The gas absorption and emission characteristics are calculated using the statistical narrow-band model. The impact of shielding properties on gas radiation is also considered by fitting functions for the length and volume of the gas-visible region. The computational efficiency and accuracy of the model are verified by comparison with the discrete transfer method. The results show that the rapid prediction model can shorten the computation time of the tail infrared radiation from several hours to about 1 s, and the outcomes of the model align well with the discrete transfer method in terms of trend and value. The maximum relative error in total infrared radiation intensity for different shielding properties of serpentine nozzles and various nozzle working conditions is only 6.5%. Furthermore, the maximum relative errors for wall radiation and gas radiation are 4.1% and 5.2%, respectively. The model also demonstrates good generalizability for axisymmetric and two-dimensional nozzles.