Calculation method for hypersonic plume infrared radiation based on a fast line-by-line calculation model

To investigate the infrared radiation characteristics of plumes of hypersonic vehicles in near space, a computational methodology for the flow field of the near space plume infrared radiation was developed. Initially, the numerical simulation of the plume flow field is carried out by using the nonlinear coupling constitutive relationship model, and the accuracy of the flow field calculation model is verified. Subsequently, a comprehensive dataset consisting of 46 200 sets of flow field characteristic parameters and absorption coefficients was generated using a line-by-line calculation physical model, informed by a full-factorial experimental design. This dataset was employed to train an accelerated line-by-line calculation model based on a BP neural network. The trained model demonstrated a maximum mean absolute error of 0.003 65 and an R² value of 0.999 4, achieving computational speeds four times faster than the traditional line-by-line calculation physical model. Finally, combined with the Backward Monte Carlo method as the infrared radiation transmission method, the infrared radiation calculation method of the hypersonic vehicles plume flow field is established. The infrared radiation characteristics of the plume under the cruising state of X-51A aircraft were studied by using the established flow field and infrared radiation calculation methods. The findings indicate that hypersonic plumes in near space exhibit a phenomenon where external heat flow envelops a cooler internal flow. Furthermore, the infrared radiation is stronger in the stagnation region at the plume's periphery, resulting in a “scissors” pattern in infrared imaging. Variations in the shear layer significantly influence the infrared imaging characteristics of the plume.