Influence of design parameters on infrared radiation characteristics of serpentine nozzles under complex flow conditions

To investigate the influence and generation mechanism of design parameters on the infrared radiation characteristics of serpentine nozzles under complex flow conditions generated in the mixing chamber of aviation engines, this study employs numerical simulation methods to calculate the infrared radiation characteristics of serpentine nozzles with different aspect ratios and length-diameter ratios. All serpentine nozzle models meet the constraint of completely shielding the high-temperature components. Additionally, the study analyzes the coupling mechanism between complex non-uniform flow and infrared radiation characteristics with different design parameters. The research findings indicate that the longitudinal vortex generated by the lobed mixer in the mixing chamber entrains high-temperature gas impacting the nozzle wall, leading to a large area of hot spots appearing on the upper and lower walls of the serpentine nozzle. On the vertical detection plane, the total infrared characteristic level increases by 1.22 times compared to that on the horizontal detection plane. As the aspect ratio increases, the hot spot area enlarges due to the intensified longitudinal vortex attachment, while the jet length decreases because of the enhanced atmospheric mixing. Consequently, the total infrared characteristic level on the vertical detection plane remains nearly unchanged, whereas that on the horizontal detection plane decreases by 30.5% due to the minor influence of hot spots. When the length-diameter ratio is small, flow separation occurs inside the serpentine nozzle due to the large curvature of the wall. The intensity of the hot spots on the wall surface significantly increases, causing the total infrared characteristic level on the horizontal and vertical detection planes to increase by 23.5% and 38.6%, respectively, compared to the cases with-out flow separation. With further increase in the length-diameter ratio, the hot spots on the wall expand due to the full mixing of the core flow and the bypass flow, resulting in 15.0% and 29.4% increase in total infrared characteristic level on the horizontal and vertical detection planes, respectively.