Effect of exit aspect ratio on internal and external flow characteristics in integrated serpentine nozzles

The integration of serpentine nozzles into Blended Wing Body (BWB) aircraft enhances stealth capability, yet the flattened afterbody mandates an asymmetric integrated outlet whose single-sided expansion induces flow distortion and thrust misalignment. The exit Aspect Ratio (AR) thus emerges as a critical design parameter governing nozzle curvature, outlet flattening, and integration quality. Using numerical methods validated against experimental pressure data and schlieren visualization, this study examines the influence of exit AR on internal flow, wave structures, and jet evolution under sea-level static and high-altitude cruise conditions. Increasing the AR enhances internal flow uniformity by mitigating longitudinal pressure variations, albeit at the cost of elevated wall temperatures from coolant-layer thinning. The asymmetric outlet generates complex three-dimensional bowl-shaped expansion waves and arcuate shock fronts; higher AR configurations suppress shock-induced boundary layer separation, reducing the thrust misalignment angle by 3.6°. Externally, the AR exerts a regime-dependent bifurcated influence on jet evolution: a higher AR shortens the jet core via mixing-dominated mechanisms in attached flow, whereas it prolongs the core by inhibiting separation-induced dissipation in separated flow. The “axis switching” arising under aft-deck and sidewall confinement yields a distinctive “Y”-shaped cross-section, enlarging the lateral projected area and modifying the detectable signature. By uncovering this regime-dependent bifurcation, the study establishes a quantitative trade-off framework in which moderately high aspect ratios optimally balance thrust stability and plume compactness against the thermal penalty, providing actionable guidance for integrated serpentine nozzle design.