Sensitivity Analysis of Infrared Radiation from Tailless Aircraft Nozzle Caused by Incoming Conditions

Exhaust system is the most important infrared radiation source of aircraft. The special geometric structure of serpentine nozzle can partially or completely block the internal high-temperature components. It can enhance the mixing between high-temperature gas and external low-temperature atmosphere with two-dimensional nozzle, and can effectively reduce the infrared radiation intensity of aircraft. The distribution characteristics of nozzle wall temperature, gas temperature and pressure and gas component concentration under different flight parameters are analyzed. Based on the discrete transfer method, the infrared radiation characteristics of nozzle are evaluated, and the influence of incoming flow parameters on the infrared radiation characteristics of nozzle is obtained. Taking flight altitude H, flight Mach number Ma, nozzle mainstream total pressure P₀ and nozzle mainstream total temperature T₀ as uncertain input parameters, samples are constructed by Latin Hypercube Sampling (LHS), and the infrared radiation response values corresponding to each sample point are calculated. The sensitivity analysis of infrared radiation signals is carried out by Non-intrusive Polynomial Chaos (NIPC) method, and the influence degree of single variable and multiple variables on the infrared radiation characteristics of nozzle is quantified. Infrared radiation intensity is the most sensitive to the total temperature of the nozzle. The Sobol index of gas radiation, wall radiation and total radiation and its total temperature reaches above 0.7, which is dominant. The contribution of Mach number to infrared radiation intensity can be ignored basically. Infrared radiation intensity is also sensitive to flight altitude. The gas radiation is the most sensitive to the flight altitude, but the total radiation is the most sensitive to the temperature, and the infrared radiation intensity mainly comes from the wall radiation in the direction of 90 degrees of horizontal detection plane and 90 degrees of vertical detection plane.